HUMAN FACTOR FOR AVIATION AND EASA TRIANING

HUMAN FACTOR FOR AVIATION AND EASA TRIANING

1. PIA Training Centre (PTC)
Human Factors

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HUMAN FACTORS

Chapter 1 – INTRODUCTION TO HUMAN FACTORS
Chapter 2 – HUMAN PERFORMANCE AND LIMITATIONS
Chapter 3 – SOCIAL PSYCHOLOGY
Chapter 4 – FACTORS AFFECTING PERFORMANCE
Chapter 5 – PHYSICAL ENVIRONMENT
Chapter 6 – TASKS
Chapter 7 – COMMUNICATION
Chapter 8 – HUMAN ERRORS
Chapter 9 – HAZARDS IN THE WORK PLACE

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Amendment No.
Section /
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Issue 1, Rev 0 All Mar 2014

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Human Factors
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GENERAL

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Contents

SECTION 1: INTRODUCTION ----------------------------------------------------- 1
SECTION 2: THE NEED TO TAKE HUMAN FACTORS INTO ACCOUNT-- 4
2.1 FUTURE PREDICTIONS -------------------------------------------------------- 4
2.2 AIRCRAFT MAINTENANCE --------------------------------------------------- 4
2.3 WHAT IS “HUMAN FACTORS”? --------------------------------------------- 5
2.4 SUBSET DEFINITIONS --------------------------------------------------------- 6
2.5 ORIGINS OF HUMAN FACTORS --------------------------------------------- 8
GENESIS ----------------------------------------------------------------------------- 8
WORLD WAR II -------------------------------------------------------------------- 8
POST WAR DEVELOPMENTS --------------------------------------------------- 8
2.6 MODERN FOCUS --------------------------------------------------------------- 9
2.7 HUMAN-MACHINE COMPARISON ----------------------------------------- 9
2.8 HUMAN-MACHINE DIFFERENCES ----------------------------------------- 11
2.9 THE IMPORTANCE OF AN EFFECTIVE HUMAN FACTORS
PROGRAMME IN A MAINTENANCE ORGANIZATION --------------------- 11
2.10. THE COST EFFECTIVENESS OF IMPLEMENTING HF PROGRAMS IN
ORGANIZATIONS ------------------------------------------------------------------- 12
2.11 DEFINITION - HUMAN FACTORS PRINCIPLES ------------------------- 12


SECTION 3: INCIDENTS ATTRIBUTABLE TO HUMAN FACTORS /
HUMAN ERROR ------------------------------------------------------------------- 14
CCC → HPIM → MRM ------------------------------------------------------------ 14
SECTION 4: MURPHY’S LAW --------------------------------------------------- 17

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SECTION 1: INTRODUCTION

Many people in the aviation industry wonder why Human
Factors training is seen as being a vital element in their overall
training syllabus. The answer is very simple. We kill people.
Anybody who has any connection with the aviation industry –
whether it be flight crew, engineers, baggage handlers, stores
people, admin staff - all play a vital part in flight safety. We all
have the potential to make mistakes which can ultimately lead
to an aircraft accident.

By understanding how mistakes are made and how they can be
avoided, we can go a long way to reducing the number of
accidents.

To gain this understanding, we must know a little of how the
human body works, how the brain processes information
received, a little psychology, how we interact with others
through effective communication and then learn the types of
human error and ways of avoiding these errors.

All elements within aviation must work together to achieve the
ultimate goal – safe and efficient flight operations, to minimise
accidents and incidents and when these do happen, to
investigate the causes (including the underlying hidden causes)
and put in place Procedures to minimise the risk of the accident
or incident happening again.

An understanding of the importance of human factors to aircraft
maintenance engineering is essential to anyone considering a
career in aircraft maintenance. Human factors impinges on
everything maintenance personnel do in the course of their job

in one way or another, from communicating effectively with
colleagues to ensuring they have adequate lighting to carry out
their tasks. Knowledge of this subject has a significant impact
on the safety standards expected of the aircraft maintenance
personnel.

Whilst this text has been prepared for those who are working in
aircraft maintenance engineering environment, it is also relevant
to all staff who are wishing to qualify as certifying staff under
EASA Part 66. Thus whilst the term ‘engineer’ has been used
throughout the document, it is generally used in a generic sense
to include all aircraft maintenance technicians, fitters, licensed
engineers, inspectors and supervisors and in some cases, it
also includes managers, planners, etc.

Human Factors and Error Management is a combination of
common sense and proven scientific knowledge about the way
daily work is done. The information received in this course
centres around the actions and inactions of the individual in the
work place and considers systems that are designed to discover
and correct errors before they have any negative impact on
safety.

The principles associated with this subject area reflect the facts
that as human errors are subjected to be made. If it is accepted
that errors are subjected to be made, then a policy of zero error
tolerance is unlikely to be an effective safeguard against any
errors eventually having harmful effects on operations.
Therefore, a policy of error management is much more likely to
result in safe operations. This subject, then, is concerned about
recognizing the variety of factors that affect humans, both
positively and negatively, when daily work are done and about

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picking up any errors that might be made and managing them
such that both the frequency and impact of incidents and
accidents in the workplace are reduced.

Aircraft maintenance is an essential component of the aviation
system which supports the global aviation industry. As air traffic
grows and the stringent requirements of commercial schedules
impose increased demands upon aircraft utilization, the
pressures on maintenance operations for on-time performance
will also continue to escalate. This will open further windows of
opportunity for human error and subsequent breakdowns in the
system's safety net. There is no question that human error in
aircraft maintenance has been a causal factor in several air
carrier accidents. It is also beyond question that unless the
aviation industry learns from these occurrences, maintenance-
related safety breakdowns will continue to occur. From a
Human Factors perspective, important truths have been
uncovered during the investigation of these occurrences.









According to the FAA National Plan for Aviation Human
Factors and other data analyses, human error has been
identified as a causal factor in 60-80% of aviation
accidents and incidents.
Fig 1.1 Aircraft Accident Attributed to Crew Error
Exacerbated by Fatigue and Extreme Weather Conditions
(National Transportation Safety Board)

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Two nuclear reactor incidents, Three Mile Island and
Chernobyl, were attributed to the poor design of
indicators and controls. (Department of Energy, DOE,
photo)
Fig 1.2 Chernobyl Radioactive Material Spread in
Northern Hemisphere, Day 10

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SECTION 2: THE NEED TO TAKE HUMAN F ACTORS INTO
ACCOUNT

Where human beings are involved in work the possibility of error
is always present. This factor must be recognised and dealt with
in aircraft operation and maintenance by every person who
contributes to airworthiness and safety.

The early pioneers in aviation were motivated by the challenge
of flight and were prepared to take the risks with perhaps little
regard to the safety of others. Flying was seen as a sport.
However, as aircraft designs improved and transport services
and routes grew the owners and customers wa nted a
successful outcome to the venture. So started the philosophy of
flight safety. It was soon discovered that after mechanical
problems, the human error problem was the next biggest factor
in flight safety. The better understanding of design has given us
reliability and the air transport industry has a very good safety
record today compared to other modes of transport. The human
problem has been more difficult to solve.

Recent statistics show that about 70-80% of aviation accidents
are caused by human error, the pilot error problem having a
higher profile. However, maintenance induced accidents are
growing in number year on year and are causing concern.








2.1 FUTURE PREDICTIONS

The worldwide commercial aviation major accident rate has
been nearly constant over the past two decades. While the rate
is low, increasing traffic over the years has resulted in the
absolute number of accidents also to increase. It is expected
for air travel to increase over the coming decades, doubling by
2017. Without improvement in the accident rate such volume in
traffic would lead to 50 or more major accidents a year. One a
week would have an unacceptable impact upon the public’s
confidence in the aviation industry.

2.2 AIRCRAFT MAINTENANCE

The Human Factor course and notes cover the Module 13 of
BCARs section L and JAR 66 Module 9 requirements to make
Aircraft Maintenance Engineers aware of the possible dangers
in aircraft maintenance due to their own performance and
others. To be aware of conditions that increase the possibility
of human error and identifying ways of reducing errors, develop
a positive, professional approach in the training of ab-initio
aircraft engineers and perhaps develop a new awareness and
culture change in the mature student. It is a requirement of
EASA PART 145:35 that human factors are part of continuation
training whilst working in an approved maintenance
organisation.

In addition to these training notes, reference notes should be
made to the UK CAA Human Factors Handbook, issue dated 8
August 2000, CAP, 715, CAP 716 and CAP 718.

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2.3 WHAT IS “HUMAN FACTO RS”?

The term “human factors” is used in many different ways in the
aviation industry. The term is, perhaps, best known in the
context of aircraft cockpit design and Crew Resource
Management (CRM). However, those activities constitute only a
small percentage of aviation-related human factors, as broadly
speaking it concerns any consideration of human involvement in
aviation. The use of the term “human factors” in the context of
aviation maintenance engineering is relatively new. Aircraft
accidents such as that to the Aloha aircraft in the USA in 1988
and the BAC 1-11 windscreen accident in the UK in June 1990
brought the need to address human factors issues in this
environment into sharp focus. This does not imply that human
factors issues were not present before these dates nor that
human error did not contribute to other incidents; merely that it
took an accident to draw attention to human factors problems
and potential solutions.

Before discussing how these accidents were related to human
factors, a definition of human factors is required. There are
many definitions available. Some authors refer to the subject as
‘human factors’ and some as ‘ergonomics’. Some see “human
factors” as a scientific discipline and others regard it as a more
general part of the human contribution to system safety.
Although there are simple definitions of human factors such as:
“Fitting the man to the job and the job to the man”, a good
definition in the context of aviation maintenance would be:

"Human factors" refers to the study of human capabilities and
limitations in the workplace. Human factors researchers study
system performance.

That is, they study the interaction of maintenance personnel, the
equipment they use, the written and verbal procedures and
rules they follow, and the environmental conditions of any
system. The aim of human factors is to optimize the relationship
between maintenance personnel and systems with a view to
improving safety, efficiency and well-being”.

Thus, human factors include such attributes as:

 human physiology

 Psychology (including perception, cognition, memory,
social interaction, error, etc.)

 work place design

 environmental conditions

 anthropometrics (the scientific study of measurements of
the

 human body)

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2.4 SUBSET DEFINITIONS

Ergonomics - The study of work

Anthropometrics – The science of measurement and the art of
application that establishes the physical geometry, mass
properties, and strength capabilities of the human body

The study of Anthropometrics (human measuremen t) is
concerned with the physical sizes and shapes of humans. Of
particular interest are the differences between and among
different populations (men vs. women, Northern Europeans vs.
Japanese).

Anthropometrics literally means man (anthro) measurements
(metric). It is the measurement of the size and proportions of
the human body, as well as parameters such as reach and
visual range capabilities. Accurate data on height, weight, limb,
and body segment sizes are needed to design items ranging
from clothing, furniture, automobiles, buses, and subway cars to
space shuttles and space stations. Anthropometrics enables us
to properly size items, including system interfaces, to "fit" the
user.










Biomechanics – Addresses issues of movement, leverage, and
strength.

Biomechanics (bio=life + machine) is the application of the
principles of mechanics and physics to measure the forces
exerted by and upon living forms. Human Factors is principally
concerned with occupational biomechanics which is the
application of these principles to the measurement of forces
exerted by and upon the human body during the performance of
work. These measurements are used to determine physical
work performance tolerances with the goal of maximizing work
performance while protecting worker occupational health and
safety.

The application of the principles of mechanics and lever
systems to the human body requires the use of anthropometric
data, critical data being the distance/length of body levers
(bones) between joints.

Human variability in physical size (static anthropometry) and
physical strength (dynamic anthropometry) is also important in
biomechanics with respect to the worker population in terms of
gender, age, and ethnicity. Above is an example of
biomechanical calculations of the forces acting upon the
lumbosacral joint during a lifting task. Note, the forces differ
between males and females because of gender dependent
differences in body segment proportions. That is, the majority of
females have shorter legs and longer torsos than males.

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2.5 ORIGINS OF HUMAN FAC TORS

GENESIS

Many people would argue that the development of human
Factors is necessarily as old as the development of aviation.
This is because human factors are part and parcel of any
development on aviation and, therefore, their development
would be considered parallel. This is however, a fairly simplistic
view and it would be fair to say that human factors as a
discipline is a reasonably modern initiative. That is not to say
that elements Of human factors such as those coming under the
headings of Anthropometrics or biomechanics have not been
taken into account well before the term “human factors” was
associated With them.

WORLD WAR II

World war ii probably provided the genesis of subject areas that
Now considered being part of human factors. What was meant
Is that specific research was conducted on aeroplane
operations And maintenance with the prime intension reducing
accident and Incident rates. In 1939, Sir Frederic Bartlett in his
Cambridge University laboratories was the first to build aircraft
cockpit mock-Ups and simulators for the prime purpose of
conducting Experiments that would reduce pilot error during
training as well As war operations.

Early researchers made significant safety advances through
Human factor applications, though these were primarily in the
Fields of anthropometrics, biomechanics and bio- physiology.


POST WAR DEVELOPMENT S

Shortly after the war, in 1949, the ergonomics research society
was founded in England. This society was the foundation of
what later became the ergonomic society and the prime
Repository of human factors research from all over Europe.
Meanwhile, a similar body was undertaking work in United
States. This body first took on the name “human factors
Society” in 1957 and the centre of research for human factors
throughout North America. In many respects, these two
Organizations developed in parallel and even replicated each
Other’s work. It was not until recently that they joined into a
Single entity that is now known as “the human factors and
Ergonomics society”.

Human factors really started to get the attention of decision
Makers in aviation following the major disaster at Tenerife in
1977 when a klm 747 ran into a pan American 747 during
Takeoff at los rodeos airport. This accident was the catalyst for
Klm to engage a number of academics under the direction of
Captain frank hawkins to put together the first course (“khufac”
standing for klm human factors) aimed at Educating flight crew
on reducing and managing errors through Knowledge of human
factor concepts. Also in the late 70’s, there were a number of
accidents and incidents to us carriers that resulted in insurance
companies asking for the airlines to Rethink their educational
strategies of flight crew. Cockpit Resource management (crm)
courses were the result of these Deliberations and they were
actively taken up by most airlines in the world who could see a
tangible benefit in educating their Flight crew in human factor
concepts.

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2.6 MODERN FOCUS

Following two significant mishaps in England, Cockpit Resource
Management had transformed into Crew Resource
Management. The two specific incidents involved scenarios in
which the cabin crew had information that could well have
prevented the disaster but it was not passed on to the captain in
time to do so. Cabin crew then became an integral part of the
safety equation on modern airliners and they too were required
to attend Human Factors courses with the express intention of
reducing and managing human error.

It did not long for senior management personnel in airlines to
realize that these Human Factors elements played a significant
role in the success or failure of the entire organization. The term
“Corporate Resource Management” or “Company Resource
Management” was coined by some to reflect the fact that these
Human Factors skills should be thought to everyone in the
organization. This is in effect what have become Human
Factors and Error Management today. Many Regulatory
authorities have also gone so far to require such courses to be
taken for licensing purposes.

In the maintenance engineering discipline, Human Factors and
Error Management have evolved into Maintenance Error
Management (MRM). MRM can be defined as:
“Maintenance Resource Management is a general process for
improving communication, effectiveness, and safety in airline
maintenance operations. MRM improves safety by increasing
the coordination and exchange of information between team
members, between teams of airline maintenance crews.

MRM programs link and integrate traditional human factor
topics, such as equipment design, human physiology, workload,
and workplace safety. Likewise the goal of any MRM program is
to improve work performance and safety. They do this by
reducing maintenance errors through improved coordination
and communication.”

2.7 HUMAN-MACHINE COMPARISON

Early in the development of Human Factors as a discipline, Paul
Fitts proposed the following comparison of human and machine
abilities. Although rapid advances in technology promise to
significantly increase "machine" abilities, this summary remains
valid and a "classic" in the Human Factors field.

Humans surpass Machines in ability to:

1 Detect small amount of visual and acoustic energy

2 Perceive patterns of light or sound

3 Improvise and use flexible procedures

4 Store very large amounts of information for long periods
and to recall relevant facts at the appropriate time

5 Reason inductively

6 Exercise judgment

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Machines surpass Humans in ability to:

1 Respond quickly to control signals, and to apply great
force smoothly and precisely

2 Perform repetitive, routine tasks

3 Store information briefly and then to erase it completely

4 Reason deductively, including computational ability

5 Ability to handle highly complex operations--to do many
different things at once.

Humans are better than Machines in:

 Sensory Functions

 Perceptual Abilities
- Stimulus Generalization
- Abstract Concepts

 Flexibility
- Ability to Improvise

 Judgment

 Selective Recall

 Inductive Reasoning



Machines are better than Humans in:

 Alertness

 Speed and Power

 Sensor Detection Outside Human Range

 Routine Work

 Computation

 Short-term Memory Storage

 Simultaneous Activities

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2.8 HUMAN-MACHINE DIFFERENCES

Other major differences between humans and machines are:
 Machines can be modified, redesigned, and retrofit --
humans cannot. Humans are born with innate,
genetically determined differences that are shaped by
the environment. Innate aptitudes or abilities are
developed through education and training.
 Machines can be manufactured to be identical--with
identical, or nearly identical, output or performance.
Humans are not identical and vary across all sensory,
cognitive, physical and performance characteristics.
Specific aspects of human performance can be made
more equal through education and training.

2.9 THE IMPORTANCE OF AN EFFECTIVE HUMAN
FACTORS PROGRAMME IN A MAINTENANCE
ORGANIZATION

Humans have performance limitations:-

 Therefore they make errors

Effective Human Factors programs train employees and put
systems in place to pick up those errors:-

 Therefore those errors do not result in delays, incidents
or accidents

Fewer errors by engineers’ means reduced delays, incidents
and accidents:-

 Therefore the company is safer and more cost efficient

A safer, more cost efficient, company means:-

 Fewer delays
 Fewer injuries to employees
 Better company performance
 And therefore better work place for its workers

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2.10 THE COST EFFECTIVENE SS OF IMPLEMENTING H F
PROGRAMS IN ORGANIZA TIONS

There are two primary reasons for including HF programs in
organizations. They are:

 Safety, and
 Cost

Safety has two aspects to it.

 First and foremost is public safety

Organizations that are better trained and present fewer
errors in their routine and emergency work present a
safer option to the travelling public. Passengers prefer to
travel with a safer airline.

 And second is on-the-job safety for maintenance
workers

Reduced error rates are reflected in the injury rates
amongst staff and less down time for workers. It is worth
noting here that those injuries aren’t always physical.
Cost savings are a bit more tangible than safety as a reason to
implement HF programs and therefore easier to identify with. It
is very difficult to prove to an accountant that an accident is
saved from occurring but it is easier to show book figures that
show definitive cost savings. Ironically, the biggest cost savings
are in reduced accident rates. It is just that in ultra-safe systems
such as aviation, the accident rates are so small that they
become statistically insignificant.

 There are cost savings through fewer operational delays
and quicker turnaround times for equipments

 And there are reduced costs through less downtime on
equipment and workers caused by errors

In summary, implementing HF programs in organizations
reduces the overall cost of maintenance. Organizations are
known to have run many HF programs within the different
branches of the organization.

2.11 DEFINITION - HUMAN FACTORS PRINCI PLES

“Principles which apply to aeronautical design, certification,
training and operations and which seek safe interface between
the human and other system components by proper
consideration to human performance.”

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SECTION 3: INCIDENTS ATTRIBUTAB LE TO HUMAN
FACTORS / HUMAN ERRO R

Maintenance errors are not some new phenomenon, but with
the advent of more reliable aircraft, and human factor training
for aircrew, the maintenance component as the cause of an
aircraft accident has become more noticeable.

3.1 CCC → HPIM → MRM

Continental airlines first came up with the term “crew
coordination concept” (CCC) to include engineers in their crew
resource management workshops. An air Ontario accident at
Dryden in Ontario led to a specific course called “human
performance in maintenance” (HPIM) and the current evolution
of these programmers has become “maintenance resource
management (MRM) which is organization specific rather than
generic. It has the added advantage of just targeting those
issues that relate to maintenance engineers rather than flight
crew and cabin crew as well.

THE HUMAN FACTORS ELEMENTS THAT CAN EVIDENT
WHEN CARRYING OUT SPECIFIC AIRCRAFT MAINTE -
NANCE TASKS SUCH AS INSPEECTION OF AGING AIR -
CRAFT AND OTHER REPETITIVE AND BORING ACTIVES.

The HPIM Initiative following the Ontario accident led to
maintenance engineering focus group identifying what has been
termed: “the dirty dozen” of maintenance engineering. These
are all human factors. They are:

 Lack of communication
 Complacency
 Lack of knowledge
 Distraction
 Lack of teamwork
 Fatigue
 Lack of resources
 Pressure
 Lack of assertiveness
 Stress
 Lack of awareness
 Norms

With respect to lack of communication, this has been a well –
established cause of error in the aviation industry and had been
included on CRM courses since they first began, so it is no
surprise to see this as one of the dirty dozen. Lack of
communication in this context means not passing on
information, written or oral, and more particular, passing on
information but not being sure that it has been understood
properly.

Complacency is a real danger for engineers. Following the
Aloha incident, the FAA issues an airworthiness directive (AD)
requiring the close visual inspection of 1300 rivets on every
single Boeing 737. If ever there was an opportunity for
complacency in the inspection business, it was provided by the
FAA in this case.

In terms of lack of knowledge, it is impossible to know all there
is to know in the maintenance engineering business. In the
absence of specific knowledge, it is a human trait to fill in the
gaps with “ good enough” actions or nothing, hiding behind the
expression” I didn’t know what to do”.

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Distractions in the engineering business are common.
Irrespective of whether the distraction is home life or just a
friend at work interrupting when work is done, distractions have
been cited on many occasions as the reason for checks or
steps being missed during an engineering process.

Teamwork, or rather the lack of it will be cited a number of
times in this course as a major source of error. Humans are all
members of a number of teams and it is important that they play
their role in each team to the best of their ability.

Fatigue has been recognized as a source of error for a long
time now but aviation personal works in a 24 hour industry and
the demands are high. Education would seem to be the major
countermeasure to this problem at the moment but more on that
later.

Lack of resources is unlikely to be a problem in most
organization but there will be times when the person might say ‘I
wish I had just one more person to help us with this job’ or
‘where are the spare floodlights when you need them’. It is easy
to improvise but it is also easy to get caught out improvising.

Pressure comes in many and varied forms. Time pressure, for
example, will always be part of the aviation industry and
particularly for engineers. An aircraft cannot make any money
when it is on the ground and the sooner it can be turned around
the better. Peer pressure could make a person work late hours
at the expense of the person’s family life and the expectations
of managers can lead to pressures to work harder or further
their education outside the normal working day. These can all
reduce attention to detail when it is most needed – prime
breeding ground for errors.

Lack of assertiveness is generally a result of the hierarchy or
rank structure in an organization. There are both formal and
informal versions. The formal ones are normally part of the
company or profession structure whiles the informal ones are
related to where a person perceives oneself amongst peers and
the organization. There is an inclination for individuals to react
according to their status rather than to their competence or
ability. This is a big issue when it comes to inspection and
checking, which are two of the prime roles of maintenance
engineers.

Stress is part and parcel of everyday lives. Despite urban
mythology to the contrary, stress cannot be left behind from
one’s personal lives. When a person goes to work, and simple
things such as an argument with the person’s spouse or partner
at home in the morning can result in errors at work.

Situation awareness is also a big problem in the aviation
industry and there is a whole module at the end of this course
devoted specifically to situation awareness.

Norms are a part of the culture of an origination and each
organization has sets of norms which are positives and those
which are negative. The trick is to enhance the positive and
suppress the negative.

The accident involving Aloha flight 243 in April 1988 involved 18
feet of the upper cabin structure suddenly being ripped away in
flight due to structural failure. The Boeing 737 involved in this
accident had been examined, as required by US regulations, by
two of the engineering inspectors. One inspector had 22 years
experience and the other, the chief inspector, had 33 years
experience. Neither found any cracks in their inspection.

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Post accident analysis determined there were over 240 cracks
in the skin of this aircraft at the time of the inspection. The
ensuing investigation identified many human-factors-related
problems leading to the failed inspections. As a result of the
Aloha accident, the US instigated a programme of research
looking into the problems associated with human factors and
aircraft maintenance, with particular emphasis upon inspection.

An incident in the UK in August 1993 involved an Airbus 320
which, during its first flight after a flap change, exhibited an un-
demanded roll to the right after takeoff. The aircraft returned to
Gatwick and landed safely. The investigation discovered that
during maintenance, in order to replace the right outboard flap,
the spoilers had been placed in maintenance mode and moved
using an incomplete procedure; specifically the collars and flags
were not fitted. The purpose of the collars and the way in which
the spoilers functioned was not fully understood by the
engineers. This misunderstanding was due, in part, to familiarity
of the engineers with other aircraft (mainly 757) and contributed
to a lack of adequate briefing on the status of the spoilers during
the shift handover. The locked spoiler was not detected during
standard pilot functional checks.

In the UK in February 1995, a Boeing 737-400 suffered a loss of
oil pressure on both engines. The aircraft diverted and landed
safely at Luton Airport. The investigation discovered that the
aircraft had been subject to bore scope inspections on both
Engines during the preceding night and the high pressure (HP)
rotor drive covers had not been refitted, resulting in the loss of
almost all the oil from both engines during flight. The line
engineer was originally going to carry out the task, but for
various reasons he swapped jobs with the base maintenance
controller.

The base maintenance controller did not have the appropriate
paperwork with him. The base maintenance controller and a
fitter carried out the task, despite many interruptions, but failed
to refit the rotor drive covers. No ground idle engine runs (which
would have revealed the oil leak) were carried out. The job was
signed off as complete.

In all three of these UK incidents, the engineers involved were
considered by their companies to be well qualified, competent
and reliable employees. All of the incidents were characterized
by the following:

 There were staff shortages
 Time pressures existed
 All the errors occurred at night
 Shift or task handovers were involved
 They all involved supervisors doing long hands-on tasks
 There was an element of a “can-do” attitude
 Interruptions occurred
 There was some failure to use approved data or
company procedures
 Manuals were confusing
 There was inadequate pre-planning, equipment or
spares

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SECTION 4: MURPHY’S LAW

EASA part 66 Module 9 syllabus also requires the inclusion of
Murphy’s Law as a topic. There are several versions of the law.
However, the most know version is the first one in the list.

 If anything can go wrong, it will.
 If there is a possibility of several things going wrong, the
one that will cause the most damage will be the one to
go wrong. Corollary: if there is a worse time for
something to go wrong, it will happen then.
 If anything just cannot go wrong, it will anyway.
 If an individual perceives that there are four possible
ways in which something can go wrong, and circumvent
these, then a fifth way , unprepared for , will promptly
develop.
 Left to themselves, things tend to go from bad to worse.
 If everything seems to be going well, something
obviously had been overlooked.
 Nature always sides with the hidden flaw.

There is a tendency among human beings towards
complacency. The belief that an accident will never happen to
“me” or to “my Company” can be a major problem when
attempting to convince individuals or organizations of the need
to look at human factors issues, recognize risks and to
implement improvements, rather than merely to pay ‘lip-service’
to human factors.

If everyone could be persuaded to acknowledge Murphy’s Law,
this might help overcome the “it will never happen to me” belief
that many people hold. It is not true that accidents only happen
to people who are irresponsible or ‘sloppy’. The incidents and
accidents described earlier show that errors can be made by
experienced, well-respected individuals and accidents can
occur in organizations previously thought to be “safe”.

Consider a bolt with seven nuts and washers labelled and
assembled as in the figure below.



How many times can it be assembled incorrectly?
How many times can it be assembled correctly as shown?

The bolt, nuts and washers can only be assembled correctly
one way. However, they can be assembled incorrectly many
different ways, which shows how much more likely it is for
components to be incorrectly assembled than correctly.

This exercise illustrates Murphy’s Law. One of the major
causes of human error in maintenance is the incorrect
installation or omission of aircraft parts and components.

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Accidents can occur because of one error or may be the result
of several quite unrelated errors.

In the latter case people/organisations may have contributed to
the accident many years prior to it actually happening. The
object of the exercise where all the work is recorded and signed
for on an aircraft means that at any time records can show who
has been involved – from the production of the raw metal, to the
designer, to the draftsman, to the manufacturer, to the
maintenance engineer.

The whole history of the aircraft and its components can be
traced back to the smallest rivet. In this way if anything goes
wrong then records will show the history and, hopefully, where
the error lies. This is not to say we need this process for
punishment purposes, but to find out what went wrong with a
view to learning and putting procedures into place that will help
prevent the same thing happening again.

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Human Factors
Chapter 2
HUMAN PERFORMANCE AND LIMITATIONS

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Contents
SECTION 1: INTRODUCTION --------------------------------------------------- 1
SECTION 2: VISION --------------------------------------------------------------- 2
2.1 VISION ----------------------------------------------------------------------- 2
THE BASIC FUNCTION OF THE EYE --------------------------------------- 2
THE CORNEA ------------------------------------------------------------------ 2
THE IRIS AND PUPIL --------------------------------------------------------- 2
THE LENS ----------------------------------------------------------------------- 2
THE RETINA -------------------------------------------------------------------- 3
2.2 FACTORS AFFECTING CLARITY OF SIGHT ---------------------------- 4
PHYSICAL FACTORS ---------------------------------------------------------- 5
OTHER VISUAL PROBLEMS INCLUDE: ----------------------------------- 5
FOREIGN SUBSTANCES ----------------------------------------------------- 5
ENVIRONMENTAL FACTORS ----------------------------------------------- 6
2.3 THE NATURE OF THE OBJECT BEING VIEWED --------------------- 7
2.4 COLOUR VISION ----------------------------------------------------------- 7
2.5 VISION AND THE AIRCRAFT MAINTENANCE ENGINEER --------- 8
SECTION 3: HEARING ------------------------------------------------------------ 9
3.1 THE BASIC FUNCTION OF THE EAR -------------------------------------- 9
OUTER EAR -------------------------------------------------------------------- 9
MIDDLE EAR ------------------------------------------------------------------- 9
INNER EAR --------------------------------------------------------------------- 9
3.2 PERFORMANCE AND LIMITATIONS OF THE EAR -------------------- 11

3.3 IMPACT OF NOISE ON PERFORMANCE -------------------------------- 11
3.4 HEARING IMPAIRMENT --------------------------------------------------- 13
3.5 HEARING PROTECTION ---------------------------------------------------- 13
3.6 PRESBYCUSIS ---------------------------------------------------------------- 14
3.7 HEARING AND THE AIRCRAFT MAINTENANCE ENGINEER -------- 14
SECTION 4: INFORMATION PROCESSING --------------------------------- 15
4.1 INFORMATION PROCESSING -------------------------------------------- 15
4.2 AN INFORMATION PROCESSING MODEL ----------------------------- 15
4.3 SENSORY RECEPTORS AND SENSORY STORES ----------------------- 15
SECTION 5: ATTENTION AND PERCEPTION ------------------------------ 17
5.1 ATTENTION AND PERCEPTION: HOW DOES IT WORK? ----------- 18
5.2 DECISION MAKING --------------------------------------------------------- 19
5.3 SITUATION AWARENESS -------------------------------------------------- 19
SECTION 6: LEARNING AND MEMORY ------------------------------------ 21
6.1 SHORT TERM OR WORKING MEMORY -------------------------------- 21
6.2 LONG TERM MEMORY (LTM) -------------------------------------------- 21
6.3 MOTOR MEMORY ---------------------------------------------------------- 22
6.4 SHORT TERM MEMORY AID --------------------------------------------- 22
SUMMARY ------------------------------------------------------------------------ 23
SECTION 7: DECISION MAKING, MEMORY, AND MOTOR
PROGRAMMES ------------------------------------------------------------------ 24
SECTION 8: CLAUSTROPHOBIA AND PHYSICAL ACCESS -------------- 25

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SECTION 1: INTRODUCTION

The intention of this chapter is to provide an overview of those
key physical and mental human performance characteristics
which are likely to affect an aircraft maintenance engineer in his
working environment, such as his vision, hearing, information
processing, attention and perception, memory, judgment and
decision making.

The human performance can be affected by physical condition
and psychological condition. The physical condition can be due
to the health of the person’s body, the environment of home and
workplace. The mental state of the person, i.e. the psychology
condition, can be due to hereditary factors, historical factors and
mental pressures. We may not be able to do much about
hereditary factors. Historical factors such as education due to a
poor early environment can be worked on and improved.
However, we can certainly look at the factors which affect
human performance mentally and physically, i.e.:

 The performance of the human body’s senses.

 The effect of the environment of the workplace on the
person.

While the precise range of human capabilities and limitations
might not be as well-defined as the performance range of
mechanical or electrical components, the same principles apply
in that human performance is likely to degrade and eventually
‘fail’ under certain conditions (e.g. stress).

Mechanical components in aircraft can, on occasion, suffer
catastrophic failures. Man, can also fail to function properly in
certain situations. Physically, humans become fatigued, are
affected by the cold, can break bones in workplace accidents,
etc. Mentally, humans can make errors, have limited perceptual
powers, can exhibit poor judgment due to lack of skills and
knowledge, etc.

In addition, unlike mechanical components, human performance
is also affected by social and emotional factors. Therefore
failure by aircraft maintenance engineers can also be to the
detriment of aircraft safety.

The aircraft engineer is the central part of the aircraft
maintenance system. It is therefore very useful to have an
understanding of how various parts of his body and mental
processes function and how performance limitations can
influence his effectiveness at work.

To have a better idea of how a person reacts with his/her
surroundings it is necessary to understand at least something of
how the body works.

The parts that will be covered are those that directly affect a
person’s ability to perform maintenance tasks namely:

 Vision
 Hearing

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SECTION 2: VISION

2.1 VISION

Of the senses, this is the most useful to man. We are more
aroused to anger or passion by visual inputs than by says feel
or smell.

The eye receives light information from the outside world and
passes it to the brain. The eye acts very similarly to a camera.
Light is taken in through the cornea and lens, a clear window at
the front of the eyeball. The cornea acts as a focusing device
and is responsible for between 70-80% of the total focusing
ability of the eye. The iris will control the amount of light
entering the eye by altering the size of the hole in the middle. It
can change shape very quickly to cater for changing light levels
i.e. luminance level up to 5 times.

THE BASIC FUNCTION OF THE EYE

In order to understand vision, it is useful first to know a little
about the anatomy of the eye (see Figure 4.1). The basic
structure of the eye is similar to a simple camera with an
aperture (the iris), a lens, and a light sensitive surface (the
retina). Light enters the eye through the cornea, then passes
through the iris and the lens and falls on the retina. Here the
light stimulates the light-sensitive cells on the retina (rods and
cones) and these pass small electrical impulses by way of the
optic nerve to the visual cortex in the brain. Here, the electrical
impulses are interpreted and an image is perceived.

THE CORNEA

The cornea is a clear ‘window’ at the very front of the eye. The
cornea acts as a fixed focusing device. The focusing is
achieved by the shape of the cornea bending the incoming light
rays. The cornea is responsible for between 70% and 80% of
the total focusing ability (refraction) of the eye.

THE IRIS AND PUPIL

The iris (the coloured part of the eye) controls the amount of
light that is allowed to enter the eye. It does this by varying the
size of the pupil (the dark area in the centre of the iris). The size
of the pupil can be changed very rapidly to cater for changing
light levels. The amount of light can be adjusted by a factor of
5:1.

THE LENS

After passing through the pupil, the light passes through the
lens. Its shape is changed by the muscles (cillary muscles)
surrounding it which results in the final focusing adjustment to
place a sharp image onto the retina. The change of shape of the
lens is called accommodation. In order to focus clearly on a
near object, the lens is thickened. To focus on a distant point,
the lens is flattened. The degree of accommodation can be
affected by factors such as fatigue or the ageing process.

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THE RETINA

The retina is located on the rear wall of the eyeball. It is made
up of a complex layer of nerve cells connected to the optic
nerve. Two types of light sensitive cells are found in the retina -
rods and cones. The central area of the retina is known as the
fovea and the receptors in this area are all cones. It is here that
the visual image is typically focused. Moving outwards, the
cones become less dense and are progressively replaced by
rods, so that in the periphery of the retina, there are only rods.

At the point at which the optic nerve joins the back of the eye, a
‘blind spot’ occurs. This is not evident when viewing things with
both eyes (binocular vision), since it is not possible for the
image of an object to fall on the blind spots of both eyes at the
same time. Even when viewing with one eye (monocular vision),
the constant rapid movement of the eye (saccades) means that
the image will not fall on the blind spot all the time. It is only
when viewing a stimulus that appears very fleetingly (e.g. a light
flashing), that the blind spot may result in something not being
seen. In maintenance engineering, tasks such as close visual
inspection or crack detection should not cause such problems,
as the eye or eyes move across and around the area of interest
(visual scanning).



Figure 2.1 the Human Eye

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2.2 FACTORS AFFECTING CL ARITY OF SIGHT

The eye is very sensitive in the right conditions (e.g. clear air,
good light, etc.). In fact, the eye has approximately 1.2 million
nerve cells leading from the retinas to the area of the brain
responsible for vision, while there are only about 50,000 from
the inner ears - making the eye about 24 times more sensitive
than the ear.

Before considering factors that can influence and limit the
performance of the eye, it is necessary to describe visual acuity.
When a person is tired accommodation is reduced, resulting in
less sharp vision (sharpness of vision is known as visual acuity).
Cones function in good light and are capable of detecting fine
detail and are colour sensitive. This means the human eye can
distinguish about 1000 different shades of colour. Rods cannot
detect colour. They are poor at distinguishing fine detail, but
good at detecting movement in the edge of the visual field
(peripheral vision). They are much more sensitive at lower light
levels. As light decreases, the sensing task is passed from the
cones to the rods. This means in poor light levels we see only in
black and white and shades of grey. Visual acuity is the ability
of the eye to discriminate sharp detail at varying distances.

An individual with acuity of 20/20 vision should be able to see at
20 feet that which the so-called ‘normal’ person is capable of
seeing at this range. It may be expressed in meters as 6/6
vision. The figures 20/40 mean that the observer can read at 20
feet what a ‘normal’ person can read at 40 feet.

Various factors can affect and limit the visual acuity of the eye.
These include:

 Physical factors such as:

 Physical imperfections in one or both eyes
(short sightedness, long sightedness)

 Age

 The influence of ingested foreign substances such as:

 Drugs
 Medication
 Alcohol
 Cigarettes

 Environmental factors such as:

 Amount of light available
 Clarity of the air (e.g. dust, mist, rain, etc.)

 Factors associated with object being viewed such as:

 Size and contours of the object
 Contrast of the object with its surroundings
 Relative motion of the object
 Distance of the object from the viewer
 The angle of the object from the viewer

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PHYSICAL FACTORS

Long sight - known as Hypermetropia - is caused by a shorter
than normal eyeball which means that the image is formed
behind the retina. If the cornea and the lens cannot use their
combined focusing ability to compensate for this, blurred vision
will result when looking at close objects.


Fig 2.2 a convex lens will overcome long sightedness by
bending light inwards before it reaches the cornea.

Short sight - known as Myopia - is where the eyeball is longer
than normal, causing the image to be formed in front of the
retina (Figure 2.3). If the accommodation of the lens cannot
counteract this then distant objects are blurred.


Fig 2.3 a concave lens will overcome short-sightedness by
bending light outwards before it reaches the cornea

OTHER VISUAL PROBLEM S INCLUDE:

 Cataracts - clouding of the lens usually associated with
ageing

 Astigmatism - a misshapen cornea causing objects to
appear irregularly shaped

 Glaucoma - a build up in pressure of the fluid within the
eye which can cause damage to the optic nerve and
even blindness

 Migraine - severe headaches that can cause visual
disturbances

Finally as a person grows older, the lens becomes less flexible
meaning that it is unable to accommodate sufficiently. This is
known as presbyopia and is a form of long sightedness.
Consequently, after the age of 40, spectacles may be required
for near vision, especially in poor light conditions. Fatigue can
also temporarily affect accommodation, causing blurred vision
for close work.

FOREIGN SUBSTANCES

Vision can be adversely affected by the use of certain drugs and
medications, alcohol, and smoking cigarettes. With smoking,
carbon monoxide which builds up in the bloodstream allows less
oxygen to be carried in the blood to the eyes. This is known as
hypoxia and can impair rapidly the sensitivity of the rods.
Alcohol can have similar effects, even hours after the last drink.

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ENVIRONMENTAL FACTOR S

Vision can be improved by increasing the lighting level, but only
up to a point as the law of diminishing returns operates. Also,
increased illumination could result in increased glare. Older
people are more affected by the glare of reflected light than
younger people. Moving from an extremely bright environment
to a dimmer one has the effect of vision being severely reduced
until the eyes get used to less light being available. This is
because the eyes have become light adapted. If an engineer
works in a very dark environment for a long time, his eyes
gradually become dark adapted allowing better visual acuity.
This can take about 7 minutes for the cones and 30 minutes for
the rods. As a consequence, moving between a bright hanger
(and the inside of an aircraft) to a dark apron area at night can
mean that the maintenance engineer must wait for his eyes to
adjust (adapt). In low light conditions, it is easier to focus if you
look slightly to one side of an object. This allows the image to
fall outside the fovea and onto the part of the retina which has
many rods.

Any airborne particles such as dust, rain or mist can interfere
with the transmission of light through the air, distorting what is
seen. This can be even worse when spectacles are worn, as
they are susceptible to getting dirty, wet, misted up or
scratched. Engineers who wear contact lenses (especially hard
or gas-permeable types) should take into account the advice
from their optician associated with the maximum wear time -
usually 8 to 12 hours - and consider the effects which extended
wear may have on the eyes, such as drying out and irritation.
This is particularly important if they are working in an
environment which is excessively dry or dusty, as airborne
particles may also affect contact lens wear. Goggles should be
worn where necessary.

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2.3 THE NATURE OF THE OB JECT BEING VIEWED

Many factors associated with the object being viewed can also
influence vision. We use information from the objects we are
looking at to help distinguish what we are seeing. These are
known as visual cues. Visual cues often refer to the comparison
of objects of known size to unknown objects. An example of this
is that we associate small objects with being further away.
Similarly, if an object does not stand out well from its
background (i.e. it has poor contrast with its surroundings), it is
harder to distinguish its edges and hence its shape. Movement
and relative motion of an object, as well as distance and angle
of the object from the viewer, can all increase visual demands.

2.4 COLOUR VISION

Although not directly affecting visual acuity, inability to see
particular colours can be a problem for the aircraft maintenance
engineer. Amongst other things, good colour vision for
maintenance engineers is important for:

 Recognizing components

 Distinguishing between wires

 Using various diagnostic tools

 Recognizing various lights on the airfield (e.g. warning
lights)

Colour defective vision is usually hereditary, although may also
occur as a temporary condition after a serious illness.

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There are degrees of colour defective vision, some people
suffering more than others. Individuals may be able to
distinguish between red and green in a well-lit situation but not
in low light conditions. Colour defective people typically see the
colours they have problems with as shades of neutral grey.

Ageing also causes changes in colour vision. This is a result of
progressive yellowing of the lens, resulting in a reduction in
colour discrimination in the blue-yellow range. Colour defective
vision and its implications can be a complex area and care
should be taken not to stop an engineer from performing certain
tasks merely because he suffers from some degree of colour
deficient vision. It may be that the type and degree of colour
deficiency is not relevant in their particular job. However, if
absolutely accurate colour discrimination is critical for a job, it is
important that appropriate testing and screening be put in place.
Colour-defective vision (normally referred to incorrectly as
colour blindness) affects about 8% of men but only 0.5% of
women. The most common type is difficulty in distinguishing
between red and green. More rarely, it is possible to confuse
blues and yellows.

2.5 VISION AND THE AIRCRAFT MAINTENANCE ENGI NEER

It is important for an engineer, particularly one who is involved
in inspection tasks, to have adequate vision to meet the task
requirements. As discussed previously, age and problems
developing in the eye itself can gradually affect vision. Without
regular vision testing, aircraft maintenance engineers may not
notice that their vision is deteriorating.

In the UK, the CAA has produced guidance which states:

“A reasonable standard of eyesight is needed for any aircraft
engineer to perform his duties to an acceptable degree. Many
maintenance tasks require a combination of both distance and
near vision. In particular, such consideration must be made
where there is a need for the close visual inspection of
structures or work related to small or miniature components.
The use of glasses or contact lenses to correct any vision
problems is perfectly acceptable and indeed they must be worn
as prescribed. Frequent checks should be made to ensure the
continued adequacy of any glasses or contact lenses. In
addition, colour discrimination may be necessary for an
individual to drive in areas where aircraft maneuver or where
colour coding is used, e.g. in aircraft wiring. Organizations
should identify any specific eyesight requirement and put in
place suitable procedures to address these issues.”

Often, airline companies or airports will set the eyesight
standards for reasons other than aircraft maintenance safety,
e.g. for insurance purposes, or for driving on the airfield.
Ultimately, what is important is for the individual to recognize
when his vision is adversely affected, either temporarily or
permanently and to consider carefully the possible
consequences should they continue to work if the task requires
good vision.

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SECTION 3: HEARING

3.1 THE BASIC FUNCTION OF THE EAR

The ear performs two quite different functions. It is used to
detect sounds by receiving vibrations in the air, and secondly, it
is responsible for balance and sensing acceleration. Of these
two, the hearing aspect is more pertinent to the maintenance
engineer, and thus it is necessary to have a basic appreciation
of how the ear works.

As can be seen in Figure 8, the ear has three divisions: outer
ear, middle ear and inner ear. These act to receive vibrations
from the air and turn these signals into nerve impulses that the
brain can recognize as sounds.

OUTER EAR

The outer part of the ear directs sounds down the auditory
canal, and on to the eardrum. The sound waves will cause the
eardrum to vibrate.

MIDDLE EAR

Beyond the eardrum is the middle ear which transmits vibrations
from the eardrum by way of three small bones known as the
ossicles, to the fluid of the inner ear. The middle ear also
contains two muscles which help to protect the ear from sounds
above 80 dB by means of the acoustic or aural reflex, reducing
the noise level by up to 20 dB. However, this protection can only
be provided for a maximum of about 15 minutes, and does not
provide protection against sudden impulse noise such as
gunfire.

It does explain why a person is temporarily ‘deafened’ for a few
seconds after a sudden loud noise. The middle ear is usually
filled with air which is refreshed by way of the eustachian tube
which connects this part of the ear with the back of the nose
and mouth. However, this tube can allow mucus to travel to the
middle ear which can build up, interfering with normal hearing.

INNER EAR

Unlike the middle ear, the inner ear is filled with fluid. The last of
the ossicles in the middle ear is connected to the cochlea. This
contains a fine membrane (the basilar membrane) covered in
hair-like cells which are sensitive to movement in the fluid. Any
vibrations they detect cause neural impulses to be transmitted
to the brain via the auditory nerve.

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Figure 2.4 the Human Ear

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3.2 PERFORMANCE AND LIMI TATIONS OF THE EAR

The performance of the ear is associated with the range of
sounds that can be heard - both in terms of the pitch
(frequency) and the volume of the sound. Volume (or intensity)
of sound is measured in decibels (dB). Table 2.1 below shows
intensity levels for various sounds and activities.



Table 2.1 Typical sound levels for various activities

3.3 IMPACT OF NOISE ON PERFORMANCE

Noise can have various negative effects in the workplace. It
can:

 Be annoying (e.g. sudden sounds, constant loud sound,
etc.)
 Interfere with verbal communication between individuals
in the workplace
 Cause accidents by masking warning signals or
messages
 Be fatiguing and affect concentration, decision making,
etc.
 Damage workers’ hearing (either temporarily or
permanently)


The amount of vibration detected in the cochlea depends on the
volume and pitch of the original sound. The audible frequency
range that a young person can hear is typically between 20 and
20,000 cycles per second (or Hertz), with greatest sensitivity at
about 3000 Hz.

Intermittent and sudden noise is generally considered to be
more disruptive than continuous noise at the same level. In
addition, high frequency noise generally has a more adverse
affect on performance than lower frequency. Noise tends to
increase errors and variability, rather than directly affect work
rate.

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3.4 HEARING IMPAIRMENT

Hearing loss can result from exposure to even relatively short
duration noise. The degree of impairment is influenced mainly
by the intensity of the noise. Such damage is known as Noise
Induced Hearing Loss (NIHL). The hearing loss can be
temporary - lasting from a few seconds to a few days - or
permanent. Temporary hearing loss may be caused by
relatively short exposure to very loud sound, as the hair-like
cells on the basilar membrane take time to ‘recover’. With
additional exposure, the amount or recovery gradually
decreases and hearing loss becomes permanent. Thus, regular
exposure to high levels of noise over a long period may
permanently damage the hair like cells in the cochlea, leading to
irreversible hearing impairment.

The UK ‘Noise at Work’ regulations (1989) impose requirements
upon employers. They stipulate three levels of noise at which an
employer must act:

a) 85 decibels (if normal speech cannot be heard clearly at 2
meters), employer must:

 Assess the risk to employees’ hearing

 Tell the employees about the risks and what precautions
are proposed

 Provide their employees with personal ear protectors
and explain their use

b) 90 decibels (if normal speech cannot be heard clearly at
1meter) employer must:

 Do all that is possible to reduce exposure to the noise by
means other than by providing hearing protection

 Mark zones where noise reaches the second level and
provide recognized signs to restrict entry

c) 140 decibels (noise causes pain)

The combination of duration and intensity of noise can be
described as noise dose. Exposure to any sound over 80 dB
constitutes a noise dose, and can be measured over the day as
an 8 hour Time Weighted Average sound level (TWA).
Permanent hearing loss may occur if the TWA is above the
recommended maximum.

3.5 HEARING PROTECTION

Hearing protection is available, to a certain extent, by using ear
plugs or ear defenders. It is good practice to reduce noise levels
at source, or move noise away from workers. Often this is not a
practical option in the aviation maintenance environment.
Hearing protection should always be used for noise, of any
duration, above 115 dB. Referring again to Table 1, this means
that the aviation maintenance engineer will almost always need
to use some form of hearing protection when in reasonably
close proximity (about 200 - 300m) to aircraft whose engines
are running.

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3.6 PRESBYCUSIS

Hearing deteriorates naturally as one grows older. This is
known as presbycusis. This affects ability to hear high pitch
sounds first, and may occur gradually from the 30’s onwards.
When this natural decline is exacerbated by Noise Induced
Hearing Loss, it can obviously occur rather sooner.

3.7 HEARING AND THE AIRC RAFT MAINTENANCE
ENGINEER

The UK CAA makes the following recommendations regarding
hearing:

“The ability to hear an average conversational voice in a quiet
room at a distance of 2 meters (6 feet) from the examiner is
recommended as a routine test. Failure of this test would
require an audiogram to be carried out to provide an objective
assessment. If necessary, a hearing aid may be worn but
consideration should be given to the practicalities of wearing the
aid during routine tasks demanded of the individual.”

It is very important that the aircraft maintenance engineer
understands the limited ability of the ears to protect themselves
from damage due to excessive noise. Even though engineers
should be given appropriate hearing protection and trained in its
use, it is up to individuals to ensure that they actually put this to
good use. It is a misconception that the ears get used to
constant noise: if this noise is too loud, it will damage the ears
gradually and insidiously. Noise levels can be reduced
(attenuated) by up to 20 decibels using ear plugs and 40
decibels using ear muffs. However, using ear protection will
tend to adversely interfere with verbal communication. Despite
this, it must be used consistently and as instructed to be
effective.

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SECTION 4: INFORMATION PROCESSI NG

4.1 INFORMATION PROCESSI NG

The previous sections have described the basic functions and
limitations of two of the senses used by aircraft maintenance
engineers in the course of their work. This section examines the
way the information gathered by the senses is processed by the
brain. The limitations of the human information processing
system are also considered.

4.2 AN INFORMATION PROCE SSING MODEL

Information processing can be represented as a model. This
captures the main elements of the process, from receipt of
information via the senses, to outputs such as decision making
and actions. One such model is shown in Figure 2.5.

4.3 SENSORY RECEPTORS AN D SENSORY STORES

Physical stimuli are received via the sensory receptors (eyes,
ears, etc.) And stored for a very brief period of time in sensory
stores (sensory memory). Visual information is stored for up to
half a second in iconic memory and sounds are stored for
slightly longer (up to 2 seconds) in echoic memory. This
enables us to remember a sentence as a sentence, rather than
merely as an unconnected string of isolated words, or a film as
a film, rather than as a series of disjointed images.

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Fig 2.5 A functional model of human information
processing

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SECTION 5: ATTENTION AND PERCEPTION

Having detected information, our mental resources are
concentrated on specific elements - this is attention. Although
attention can move very quickly from one item to another, it can
only deal with one item at a time. Attention can take the form of:

 Selective attentions

 Divided attention

 Focused attention

 Sustained attention

Selective attention occurs when a person is monitoring several
sources of input, with greater attention being given to one or
more sources which appear more important. A person can be
consciously attending to one source whilst still sampling other
sources in the background. Psychologists refer to this as the
‘cocktail party effect’ whereby you can be engrossed in a
conversation with one person but your attention is temporarily
diverted if you overhear your name being mentioned at the
other side of the room, even though you were not aware of
listening in to other people’s conversations. Distraction is the
negative side of selective attention.

Divided attention is common in most work situations, where
people are required to do more than one thing at the same time.
Usually, one task suffers at the expense of the other, more so if
they are similar in nature. This type of situation is also
sometimes referred to as time sharing.

Focused attention is merely the skill of focusing one’s attention
upon a single source and avoiding distraction.

Sustained attention as its name implies, refers to the ability to
maintain attention and remain alert over long periods of time,
often on one task. Most of the research has been carried out in
connection with monitoring radar displays, but there is also
associated research which has concentrated upon inspection
tasks.

Attention is influenced by arousal level and stress. This can
improve attention or damage it depending on the
circumstances.

Perception involves the organization and interpretation of
sensory data in order to make it meaningful, discarding non-
relevant data, i.e. transforming data into information. Perception
is a highly sophisticated mechanism and requires existing
knowledge and experience to know what data to keep and what
to discard, and how to associate the data in a meaningful
manner.

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5.1 ATTENTION AND PERCEP TION: HOW DOES IT WORK?

A proportion of ‘sensed’ data may be lost without being
‘perceived’. An example with which most people are familiar is
that of failing to perceive something which someone has said to
you, when you are concentrating on something else, even
though the words would have been received at the ear without
any problem. The other side of the coin is the ability of the
information processing system to perceive something (such as
a picture, sentence, concept, etc.) even though some of the
data may be missing. The danger, however, is that people can
fill in the gaps with information from their own store of
knowledge or experience, and this may lead to the wrong
conclusion being drawn.

There are many well-known visual ‘illusions’ which illustrate the
limits of human perception. Figure 2.6 shows how the
perceptual system can be misled into believing that one line is
longer than the other, even though a ruler will confirm that they
are exactly the same.

Figure 2.7 illustrates that we can perceive the same thing quite
differently (i.e. the letter “B” or the number “13”). This shows the
influence of context on our information processing.

In aviation maintenance it is often necessary to consult
documents with which the engineer can become very familiar. It
is possible that an engineer can scan a document and fail to
notice that subtle changes have been made. He sees only what
he expects to see (expectation). To illustrate how our eyes can
deceive us when quickly scanning a sentence, read quickly the
sentence below in Figure 2.8.

Expectation can also affect our memory of events. The study
outlined above was extended such that subjects were asked, a
week later, whether they recalled seeing glass on the road after
the collision. (There was no glass). The group, who had been
told that they would see a crash, recalled seeing glass; the
other group recalled seeing no glass.


Fig 2.6 the Muller –Layer Illusion


Fig 2.7 the importance of context


Fig 2.8 the effects of expectation

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At first, most people tend to notice nothing wrong with the
sentence. Our perceptual system sub-consciously rejects the
additional “THE”.

5.2 DECISION MAKING

Having recognized coherent information from the stimuli
reaching our senses, a course of action has to be decided upon.
In other words decision making occurs. This may range from
deciding to do nothing, to deciding to act immediately in a very
specific manner. A fire alarm bell, for instance, may trigger a
well-trained sequence of actions without further thought (i.e.
evacuate); alternatively, an unfamiliar siren may require further
information to be gathered before an appropriate course of
action can be initiated.

We are not usually fully aware of the processes and information
which we use to make a decision. Tools can be used to assist
the process of making a decision. For instance, in aircraft
maintenance engineering, many documents (e.g. maintenance
manuals, fault diagnosis manuals), and procedures are
available to supplement the basic decision making skills of the
individual. Thus, good decisions are based on knowledge
supplemented by written information and procedures, analysis
of observed symptoms, performance indications, etc. It can be
dangerous to believe that existing knowledge and prior
experience will always be sufficient in every situation as will be
shown in the section entitled ‘Information Processing
Limitations’.

Finally, once a decision has been made, an appropriate action
can be carried out. Our senses receive feedback of this and its
result. This helps to improve knowledge and refine future
judgment by learning from experience.

5.3 SITUATION AWARENESS

Although not shown explicitly in Figure, the process of attention,
perception and judgment should result in awareness of the
current situation. Situation awareness has traditionally been
used in the context of the flight deck to describe the pilot’s
awareness of what is going on around him, e.g. where he is
geographically, his orientation in space, what mode the aircraft
is in, etc. In the maintenance engineering context, it refers to
the:

 Perception of important elements, e.g. seeing loose
bolts or missing parts, hearing information passed
verbally

 Comprehension of their meaning, e.g. why is it like
this? Is this how it should be?

 Projection of their status into the future, e.g. future
effects on safety, schedule, airworthiness

As with decision making, feedback improves situation
awareness by informing us of the accuracy of our mental
models and their predictive power. The ability to project system
status backward, to determine what events may have led to an
observed system state, is also very important in aircraft
maintenance engineering, as it allows effective fault finding and
diagnostic behaviour. Situation awareness for the aircraft
maintenance engineer can be summarized as the:

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 Status of the system the engineer is working on

 The relationship between the reported defect and the
intended rectification

 The possible effect of this work on other systems

 The effect of this work on that being done by others and
the effect of their work on this work

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SECTION 6: LEARNING AND MEMOR Y

By definition, learning is the acquisition of knowledge or skill
through instruction or experience. Essentially, learning involves
the storage of information within memory as this information is
acquired through experience. The human brain must be able to
store information for as long as several decades (Long Term
Memory) or for as short a time as several seconds (Short Term
Memory). Additionally the human brain is able to transfer
information from short term to long term memory through the
process of memory consolidation. For example one can
remember a telephone number long enough to dial it or it can
be transferred to long term memory for future use.

6.1 SHORT TERM OR WORKIN G MEMORY

From the example of the telephone number we can see that if
nothing is done to try to remember then a minute or so later the
information is lost. Looking up the index in a book to find a
page number for a particular item would use this part of the
memory. Once the page is found the number is forgotten.
Unless actively rehearsed, information in working memory is
lost in about 20 to 30 seconds. Acoustic information is easier to
remember than visual because it is easier to rehearse a sound
than memorise written data.

6.2 LONG TERM MEMORY (LT M)

Long term memory can be divided into Semantic Memory and
Episodic Memory. Semantic memory is where the knowledge
is retained in the long term, where the general meaning rather
than the specific sounds of the original message are
remembered.

Information once transferred from the short term memory is
never lost. If we are unable to remember anything in this part of
the memory it is because we cannot retrieve it (recall). It is
there but we cannot find it. Confusions in LTM recollection are
much more likely to involve mixing up words rather than similar
meanings. The word ‘car’ may be recalled instead of ‘van’ for
example.

Episodic memory is that part of the memory system that deals
with ‘episodes’, specific events in your life. This part of the
memory changes over the years. It can result in similar events
becoming mixed, even into one event. This is due to the
retention rate over time - approximately only 35% is
remembered after one day and 22% after 31 days. This also
means that when asked to recall an incident, any two people will
often give conflicting reports. Therefore, if you are a witness to
an accident or incident, write your evidence down immediately,
even take photos. This will help in the interrogation later on,
when your memory is weaker on the facts you hoped to retain.
Of the two types of long term memory, semantic is said to last
longer, whereas episode is more accurate.

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6.3 MOTOR MEMORY

This memory is associated with the skill of controlling hand,
feet, leg movement etc. When performing or learning a new
task a great deal of central processing of information will be
required by the brain. Firstly in the short term memory and then
with rehearsal, stored in the long term memory.

Learning to drive a car is a good example. At the first stage of
learning, the Cognitive Stage, we have to understand what each
control in the car is for and how it works. The first time we set
off in the car we have to think hard about what we are doing.
The second stage of learning is the Associative Stage. With a
little practice each element of the driving process is learnt, for
example the use of the clutch whilst gear changing, yet still
looking ahead.

When well rehearsed, all the elements of car driving become
automatic and you are aware little conscious thought is used.
This is the automatic stage of learning when the task no longer
requires thought to perform it. Whilst driving, a conversation
can be carried out with only a monitoring function of the brain
left to check the process of driving.

6.4 SHORT TERM MEMORY AI D

To improve your chances of remembering information,
particularly numbers, it is sometimes useful to break the number
down into more easily handled ‘chunk’. For example, the
number 19391914999365 would not be easy to remember when
taken as a whole. However, we can break this number down
into more manageable chunks:

 1939 – Start of World War 2.
 1914 – Start of World War 1.
 999 – Emergency phone number in the UK.
 365 – Days in a year.

By remembering the smaller chunks, we are far more likely to
remember the larger number.

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SUMMARY
 There are three parts to memory: encoding, storage and
retrieval.

 Most material that is forgotten is lost in the first few
hours after learning. If something is still remembered
after a few days, it is unlikely to be forgotten.

 STM has a very small capacity, but the amount in the
storage can be increased by chunking. Material in STM
will be lost within 20-30 seconds if it is not rehearsed.

 LTM has a more or less unlimited capacity but the
problem is how to retrieve the information.

 Memory is not like a video-recording. When we
remember we reconstruct the event on the basis of
information available in schemata. Material can be
distorted in memory.

 Memory is most efficient where there are lots of recall
cues. When there are few recall cues it may help to be
in the same physical or mental state as you were when
you first came across the material.

 What we do before and after learning something may
interfere with later recall. This is especially true if the
interfering material is of a similar nature to the learnt
material and is presented just before or just after it.

 Physical shock can disturb memory, especially for
events that occurred up to half an hour before the shock.

 Highly emotionally charged material might be repressed.
This does not make total loss but is in the
sub-conscious. It may affect behaviour.

 Acoustic information is easier to remember as the brain
finds it easier to rehearse a sound than a visual image.

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SECTION 7: DECISION MAKING, MEM ORY, AND MOTOR
PROGRAMMES

Attention and perception shortcomings can clearly impinge on
decision making. Perceiving something incorrectly may mean
that an incorrect decision is made, resulting in an inappropriate
action. Figure 2.5 also shows the dependence on memory to
make decisions. It was explained earlier that sensory and short-
term memory has limited capacity, both in terms of capacity and
duration. It is also important to bear in mind that human memory
is fallible, so that information:

 May not be stored

 May be stored incorrectly

 May be difficult to retrieve

All these may be referred to as forgetting, which occurs when
information is unavailable (not stored in the first place) or
inaccessible (cannot be retrieved). Information in short-term
memory is particularly susceptible to interference, an example
of which would be trying to remember a part number whilst
trying to recall a telephone number.

It is generally better to use manuals and temporary aides-
memoirs rather than to rely upon memory, even in
circumstances where the information to be remembered or
recalled is relatively simple. For instance, an aircraft
maintenance engineer may think that he will remember a torque
setting without writing it down, but between consulting the
manual and walking to the aircraft (possibly stopping to talk to

someone on the way), he may forget the setting or confuse it
(possibly with a different torque setting appropriate to a similar
task with which he is more familiar). Additionally, if unsure of the
accuracy of memorized information, an aircraft maintenance
engineer should seek to check it, even if this means going
elsewhere to do so. Noting something down temporarily can
avoid the risk of forgetting or confusing information. However,
the use of a personal note book to capture such information on
a permanent basis can be dangerous, as the information in it
may be come out-of-date.

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SECTION 8: CLAUSTROPHOBIA AND P HYSICAL ACCESS

Although not peculiar to aircraft maintenance engineering,
working in restricted space and at heights is a feature of this
trade. Problems associated with physical access are not
uncommon. Maintenance engineers and technicians often have
to access, and work in, very small spaces (e.g. in fuel tanks),
cramped conditions (such as beneath flight instrument panels,
around rudder pedals), elevated locations (on cherry-pickers or
staging), sometimes in uncomfortable climatic or environmental
conditions (heat, cold, wind, rain, noise). This can be
aggravated by aspects such as poor lighting or having to wear
breathing apparatus.

There are many circumstances where people may experience
various levels of physical or psychological discomfort when in
an enclosed or small space, which is generally considered to be
quite normal. When this discomfort becomes extreme, it is
known as claustrophobia. It is quite possible that susceptibility
to claustrophobia is not apparent at the start of employment. It
may come about for the first time because of an incident when
working within a confined space, e.g. panic if unable to extricate
oneself from a fuel tank. If an engineer suffers an attack of
claustrophobia, they should make their colleagues and
supervisors aware so that if tasks likely to generate
claustrophobia cannot be avoided, at least colleagues may be
able to assist in extricating the engineer from the confined
space quickly, and sympathetically.

Engineers should work in a team and assist one another if
necessary, making allowances for the fact that people come in
all shapes and sizes and that it may be easier for one person to

access a space, than another. However, this should not be used
as an excuse for an engineer who has put on weight, to excuse
himself from jobs which he would previously have been able to
do with greater ease!

Claustrophobia can be defined as abnormal fear of being in an
enclosed space.

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Human Factors
Chapter 3
SOCIAL PSYCHOLOGY

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Contents

SECTION 1: INDIVIDUAL PERSONALITY ------------------------------ 1
1.1 INTRODUCTION ------------------------------------------------------------ 1
SECTION 2: RESPONSIBILITY ----------------------------------------- 3
2.1 RESPONSIBILITY: INDIVIDUAL AND GROUP -------------------------- 3
2.2 WORKING AS AN INDIVIDUAL OR AS A GROUP --------------------- 3
2.3 INDIVIDUAL RESPONSIBILITY -------------------------------------------- 3
2.4 GROUP OR TEAM RESPONSIBILITY ------------------------------------- 4
SECTION 3: TEAMWORKING ----------------------------------------- 5
3.1 TEAMWORK (GROUP DECISION MAKING) --------------------------- 5
CONFORMITY ------------------------------------------------------------------- 6
COMPLIANCE ------------------------------------------------------------------- 6
RISKY SHIFT --------------------------------------------------------------------- 6
GROUP DURATON ------------------------------------------------------------- 6
SECTION 4: MANAGEMENT, SUPERVISION, LEADERSHIP,
MOTIVATION & PEER PRESSURE ------------------------------------ 8
4.1 TEAM LEADER/MANAGER ----------------------------------------------- 8
4.2 THE INDIVIDUAL ------------------------------------------------------------ 9
4.3 SALARY PACKAGE ---------------------------------------------------------- 9
4.4 SHIFTS ------------------------------------------------------------------------- 9
4.5 TEAMWORK ----------------------------------------------------------------- 9


SECTION 5: PEER PRESSURE ---------------------------------------- 10
5.1 EXPERIMENTS IN CONFORMITY --------------------------------------- 10
5.2 COUNTERING PEER PRESSURE AND CONFORMITY -------------- 11
SECTION 6: MOTIVATION ------------------------------------------ 12
6.1 MASLOW’S HIERARCHY OF NEEDS ----------------------------------- 12
6.2 DE-MOTIVATION ---------------------------------------------------------- 15
SECTION 7: CULTURE ISSUES --------------------------------------- 16
7.1 SUMMARY ------------------------------------------------------------------ 17

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SECTION 1: INDIVIDUAL PERSONALITY

1.1 INTRODUCTION

It was once said ‘if all members of any social group acted alike,
thought alike and felt alike, personality would not exist’. This
statement underlines one of the most important facts about
people, namely, that each of us (even identical twins) is
psychologically different in one way or another from our fellow
man. This variation constitutes what we recognise in each other
as differences in our personalities.

Our personal differences are believed to be affected by our
genes, our environment and our social interaction. We translate
information from our senses, after using previous experience.
This may be stored in our memory as schemata (plans) and as
memory processes the information may change in its
perception. When we form impressions of other people, we do
not automatically pay attention to all the information which we
get from them. Our schemata lead us to assume certain things
about them, based on previous information in the memory,
which may be biased.

Personality

Two terms are often encountered when talking about a person’s
personality, these are:

 Character
 Temperament

Both terms have sometimes been used interchangeably with the
word personality. Furthermore it is generally assumed that each


covers a somewhat different aspect of personality. The word
‘character’ has two slightly different, though related, meanings.
One has moral connections and describes behaviour, thus
indicating a good or bad character. The second meaning
considers character from the point of view of its strength or
quality.

For example:

A weak character being considered as ‘someone with poor
impulse control’.

Temperament has also been used to guide personality i.e. if a
person is ‘hot’ tempered, ‘sweet’ tempered, and he’s
temperamental.

Personality is the term used to embrace all those stable
behavioural characteristics that are associated with an
individual and one’s personality is extremely important in
determining the relationship with others.

We are all used to the common descriptive words and phrases
used to describe individuals:

For example:
 a jolly chap’
 ‘a daredevil’
 ‘a good sport’
 ‘a sour faced skinflint’
 ‘a good listener’

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These terms, however, are unscientific and too general for use
in assessing personality with any degree of accuracy.

Assessing Personality

We all make assessments of personality in any social
encounter. Quick first impressions are made by their
appearance and dress. The person’s physical build also affects
our perception of personality. Short, fat people are seen as easy
going, sociable and self indulgent. Tall thin people as fragile,
introspective, sensitive and nervous. Muscular, square
shouldered people are seen as restless, energetic and
insensitive. We have also heard of villains being described as
‘thin lipped, murderers having close set eyes’ and thugs as
‘heavy set’. These are relearned preconceptions from our long
term memory and are ‘colouring’ our true assessment of the
individual’s personality. Personality should be assessed by
various techniques such as interviews, projective tests and
questionnaires.

Classification of Personality

Early Greeks placed people into four groups of differing
temperamental and emotional make up. These are:

 Melancholic – sad, doleful.
 Phlegmatic – slow, stolid.
 Choleric – easily moved to anger.
 Sanguine – confident, cool.

Various psychologists have attempted to classify, explain and
alter human personality traits which may be innate and in any
case are acquired very early in life. They are deep-seated
characteristics which constitute the essence of a person.

They are stable and very resistant to change. Attempts by
psychotherapy to modify personality distortions seem to have
very limited success, even when applied over many years.
Personality, attitudes and beliefs are intangible in as much as
they cannot be seen or studied directly but only inferred from
what a person says or does. Personality may be classified in a
number of dimensions. The major dimensions may be said to
be extraversion and anxiety. Other major traits such as warmth
and sociability, impulsivity, tough-mindedness, dominance,
stability and boldness will all contribute to the overall personality
of the individual.
At the very basic level extraversion may be associated with
boldness, impulsive behaviour and sociability. Anxiety is
normally linked to emotional instability, tension and
suspiciousness. As extraversion and anxiety are not related to
one another, some people may be anxious and extroverted,
others anxious and introverted.
The results from a series of tests or questionnaires may be
plotted on a simple two dimensional graph of personality with
axes of extraversion and anxiety. Most people will be about the
average in both dimensions.
As deviation from the average increases so the characteristics
of that personality become more pronounced. For example the
anxious extravert will be regarded as aggressive and
changeable, the stable introvert as thoughtful and controlled.
An anxious introvert will seem sober and pessimistic, stable
extraverts will be seen as responsive and easy going.
The anxious extrovert is likely to be a risk taker. The anxious
introvert will be more rigid and sober in behaviour and when
confronted with an emergency may not be able to perform. The
aircraft engineer, on average, has been found to be a stable
introvert, being thoughtful and controlled, not likely to take risks.

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SECTION 2: RESPONSIBILITY

2.1 RESPONSIBILITY: INDIVIDUAL AND GROUP

Being an aircraft maintenance engineer is a responsible job.
Clearly, the engineer plays a part in the safe and efficient
passage of the travelling public when they use aircraft. Within
aircraft maintenance, responsibility should be spread across all
those who play a part in the activity. This ranges from the
accountable manager who formulates policy, through
management that set procedures, to supervisors, teams of
engineers and individuals within those teams. Flight crew also
play a part as they are responsible for carrying out pre-flight
checks and walk-around and highlighting aircraft faults to
maintenance personnel.

2.2 WORKING AS AN INDIVIDUAL OR AS A GROUP

Traditionally, in the maintenance engineering environment,
responsibility has been considered in terms of the individual
rather than the group or team. This is historical, and has much
to do with the manner in which engineers are licensed and the
way in which work is certified. This has both advantages and
disadvantages. The main advantage to individual responsibility
is that an engineer understands clearly that one or more tasks
have been assigned to him and it is his job to do them (it can
also be a strong incentive to an engineer to do the work
correctly knowing that he will be the one held responsible if
something goes wrong). The main disadvantage of any
emphasis upon personal responsibility is that this may overlook
the importance of working together as a cohesive team or group
to achieve goals.

In practice, aircraft maintenance engineers are often assigned
to groups or teams in the workplace. These may be shift teams,
or smaller groups within a shift. A team may be made up of
various engineering trades, or be structured around aircraft
types or place of work (e.g. a particular hangar). Although
distinct tasks may be assigned to individuals within a team, the
responsibility for fulfilling overall goals would fall on the entire
team. If someone is considered responsible, they are liable to
be called to account as being in charge or control of, or
answerable for something.

2.3 INDIVIDUAL RESPONSIBILITY

All aircraft maintenance engineers are skilled individuals having
undertaken considerable training. They work in a highly
professional environment in the UK and generally have
considerable pride in their work and its contribution to air safety.
All individuals, regardless of their role, grade or qualifications
should work in a responsible manner. This includes not only
Licensed Aircraft Engineers (LAEs), but non-licensed staff.

“The certifying engineer shall be responsible for ensuring that
work is performed and recorded in a satisfactory manner...”
Likewise, non-certifying technicians also have a responsibility in
the maintenance process. An organization approved in
accordance with EASA part 145 must establish the competence
of every person, whether directly involved in hands-on
maintenance or not. Regulatory Authorities previously ruled that
an organisation can make provision on maintenance records or
work sheets for the mechanic(s) involved to sign for the work.
Whilst this is not the legally required certification under the
requirements of EASA part145, it provides the traceability to
those who were involved in the job.

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The LAE is then responsible for any adjustment or functional
test and the required maintenance records are satisfied before
making the legal certification.

2.4 GROUP OR TEAM RESPON SIBILITY

Group responsibility has its advantages and disadvantages. The
advantages are that each member of the group ought to feel
responsible for the output of that group, not just their own output
as an individual, and ought to work towards ensuring that the
whole ‘product’ is safe. This may involve cross-checking others’
work (even when not strictly required), politely challenging
others if you think that something is not quite right, etc.

The disadvantage of group responsibility is that it can potentially
act against safety, with responsibility being devolved to such an
extent that no-one feels personally responsible for safety
(referred to as diffusion of responsibility). Here, an individual, on
his own, may take action but, once placed within a group
situation, he may not act if none of the other group members do
so, each member of the group or team assuming that ‘someone
else will do it’.

Social psychologists have carried out experiments whereby a
situation was contrived in which someone was apparently in
distress, and noted who came to help. If a person was on their
own, they were far more likely to help than if they were in a pair
or group. In the group situation, each person felt that it was not
solely his responsibility to act and assumed that someone else
would do so.

Other recognized phenomena associated with group or team
working and responsibility for decisions and actions which
aircraft maintenance engineers should be aware of are:

 Inter-group conflict in which, situations evolve where a
small group may act cohesively as a team, but rivalries
may arise between this team and others (e.g. between
engineers and planners, between shifts, between teams
at different sites, etc.). This may have implications in
terms of responsibility, with teams failing to share
responsibility between them. This is particularly pertinent
to change of responsibility at shift handovers, where
members of the outgoing shift may feel no ‘moral’
responsibility for waiting for the incoming shift members
to arrive and giving a verbal handover in support of the
written information on the work cards or task sheets,
whereas they might feel such responsibility when
handing over tasks to others within their own shift.
 Group polarization is the tendency for groups to make
decisions that are more extreme than the individual
members’ initial positions. At times, group polarization
results in more cautious decisions. Alternatively, in other
situations, a group may arrive at a course of action that
is riskier than that which any individual member might
pursue. This is known as risky shift. Another example of
group polarization is groupthink in which the desire of
the group to reach unanimous agreement overrides any
individual impulse to adopt proper, rational (and
responsible) decision-making procedures.
 Social loafing has been coined to reflect the tendency for
some individuals to work less hard on a task when they
believe others are working on it. In other words, they
consider that their own efforts will be pooled with that of
other group members and not seen in isolation.
 Responsibility is an important issue in aircraft
maintenance engineering, and ought to be addressed
not only by licensing, regulations and procedures, but
also by education and training, attempting to engender a
culture of shared, but not diffused, responsibility.

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SECTION 3: TEAMWORKING

3.1 TEAMWORK (GROUP DECI SION MAKING)

It is generally accepted that the decision reached by a group will
be better than the average decision made by individuals within
the group, although this might take longer. The group decision
will, however, seldom improve on the problem solving ability of
the ablest group member. From this point of view, there may be
a valid reason to have the maximum number of the highest
trained personnel with vast experience of aircraft maintenance,
on all the company’s shifts. However, this is realistically not
practical, with the cost of manpower etc.

When a group are discussing and arguing on the solution to a
problem, before coming to an agreement, there are a number of
factors which will affect the group decision.

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CONFORMITY People like to conform; non-conformity is stress inducing. To
conform to a group is a way of minimising stress. People do not
normally wish to be seen as the ‘odd one out’. Individuals will
accept group opinions and attitudes. The readiness to conform
differs between sexes, nationalities and cultures. Sometimes this
group decision may be against the individual’s better judgement and
he may feel pressurised, leading to stress. This is known as PEER
PRESSURE.
Peer Pressure is helped by the team when it is motivated, close-knit,
well managed and supportive of the individual. This is not always
achievable.
COMPLIANCE This is the term used to describe an individual’s likelihood of
complying with a request. If a large and unreasonable request is
made, there is a greater likelihood of it being complied with if it has
been preceded either by an even more outrageous request that has
been denied, or if a smaller more reasonable request has already
been accepted.
RISKY SHIFT If a group is asked to consider a problem they will usually come to a
decision that is more risky than the average decision made by
individual members. If the individual members are bold, daring
personalities, such a combination will make an unduly bold
outcome. Hence the name Risky Shift.
GROUP DURATON When a team are kept together for a long period of time they come
to know each other’s habits as well as their strengths and
weaknesses. This may be an advantage until, say, a team member
falls ill. The new team member will be unaware of any signals or
shortened procedures which the team has adopted. This may lead
to a misunderstanding and a potential accident.

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Improving Group Decision Making

Guidelines can be given to improve decision making. Some of
these are given below:

 Avoid arguing for your personal judgements. Approach
the task on the basis of logic.

 Avoid changing your mind only in order to reach
agreement or avoid conflict. Support only solutions with
which you are able to agree.

 Avoid conflict reducing techniques such as a majority
vote or a middle course strategy.

 View differences of opinion as helpful rather than a
hindrance in decision making.

When these guidelines are used then a group will produce a
better performance than another group not using the guidelines.

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SECTION 4: MANAGEMENT, SUPERVIS ION, LEADERSHIP,
MOTIVATION & PEER PRESSURE

4.1 TEAM LEADER/MANAGER

The team should include everyone from the cleaners to top
management. If a person works for the company, their objective
is the same – a safe aircraft full of fare-paying passengers with
their flight on time.

The team leader should encourage the idea of team making for
reasons previously discussed. Team meetings should be held
from time to time to discuss:-

 Working conditions
 Past problems
 Company performance/team performance
 Future programme and plans
 Any anticipated future problems
 Any competent business

Problems of a private nature should be in confidence.

When a leader is heading a meeting to reach the best decision
and to maintain the morale of the team, the following principles
should be followed:

 Avoid giving any indication of your own opinion or ideas
at the outset. A team member with a different idea may
be reluctant to air it if it seems to contradict the captain.

 Do make a point of soliciting the ideas of other crew
members openly. In particular encourage them to
express any doubts or objections to a particular course
of action. Always ensure that the potential problems or
dangers are fully aired.

 When the leader has made a decision, the reasons for
arriving at that decision should be explained if there is
time. Failure to do so will make the crew members feels
that their ideas have been ignored, with the result that, in
the future, they will not be at all keen to put forward
proposals.

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4.2 THE INDIVIDUAL

From previous chapters we can see human behaviour in the
workplace can be affected by a wide number of causes. It is
difficult to quantify what affects who and by how much. An event
may affect one person adversely whilst the same event may not
affect another in any way. The amount of adverse affect will
also depend on how often a particular event happens and on
the state of mind of the person at the time.

For Example:

There being no soap in the washroom – it may affect some
more than others – it gets a bit tiresome when there has not
been any soap for several days – it is doubly annoying when
you have very dirty hands and have a particular need to have
especially clean hands before leaving work.

This is just one event but the general parameters can apply to
many other situations – harassment, spares problems,
promotion etc.

For the engineer to be happy and have a highly motivated
attitude to work we must consider a number of factors that might
affect him. Any one or more of these factors will have a
motivation/de-motivation effect.

Expectations – It is important that if a person has ambitions in
terms of promotion/progression, then he/she should have
expectations of realising them.



For some, promotion/progression is important, so firms should
have in place a worker/supervisor/management structure to
allow progression for those that have the desire to develop their
talents. For small firms this may not be so easy.

4.3 SALARY PACKAGE

Money is always a good motivator. If the overall salary package
is good it goes a long way to ensuring a happy worker. ‘Salary’
is related to expectations and can include:

 Basic salary
 Overtime working/overtime rates
 Pension schemes
 Relocation expenses
 Share certificate schemes
 Private health care schemes
 Perks such as ‘free flights’

4.4 SHIFTS

We can see, from our Circadian rhythms, shift work can affect
our sleeping patterns. This can lead to fatigue, stress and, in
the long term, health problems; a strong de-motivator.

4.5 TEAMWORK

As previously discussed, a close-knit, well managed, motivated
team with supportive management will have a high morale. The
team leader should encourage teamwork and team
responsibility.

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SECTION 5: PEER PRESSURE

In the working environment of aircraft maintenance, there are
many pressures brought to bear on the individual engineer. We
have already discussed the influence of the organization, of
responsibility and motivational drives. In addition to these, there
is the possibility that the aircraft maintenance engineer will
receive pressure at work from those that work with him. This is
known as peer pressure.

For example, an individual engineer may feel that there is
pressure to cut corners in order to get an aircraft out by a
certain time, in the belief that this is what his colleagues would
do under similar circumstances. There may be no actual
pressure from management to cut corners, but subtle pressure
from peers, e.g. taking the form of comments such as “You
don’t want to bother checking the manual for that. You do it like
this…” would constitute peer pressure.

Peer pressure thus falls within the area of conformity.
Conformity is the tendency to allow one’s opinions, attitudes,
actions and even perceptions to be affected by prevailing
opinions, attitudes, actions and perceptions.

5.1 EXPERIMENTS IN CONFO RMITY

Asch carried out several experiments investigating the nature of
conformity, in which he asked people to judge which of lines A,
B & C was the same length as line X. (see Figure 3.1). He
asked this question under different conditions:

 Where the individual was asked to make the judgment
on his own


 Where the individual carried out the task after a group of
7-9 confederates of Asch and all judged that line A was
the correct choice. Of course, the real participant did not
know the others were “stooges”

In the first condition, very few mistakes were made (as would be
expected of such a simple task with an obvious answer). In the
latter condition, on average, participants gave wrong answers
on one third of the trials by agreeing with the confederate
majority Clearly, participants yielded to group pressure and
agreed with the incorrect ‘group’ finding (however, it is worth
mentioning that there were considerable Peer pressure is the
actual or perceived pressure which an individual may feel, to
conform to what he believes that his peers or colleagues
expect. he leader should encourage loyalty to the team and
Company. Ideally all employees should be ‘Company Men’
working towards the betterment of that Company.

Further research indicated that conformity does not occur with
only one confederate (as then it is a case of ‘my word against
yours’). However, it is necessary to have only three
confederates to one real participant to attain the results that
Asch found with 7- 9 confederates.

The degree, to which an individual’s view is likely to be affected
by conformity or peer pressure, depends on many factors,
including:

 Culture (people from country x tend to conform more
than those from country y)

 Gender (men tend to conform less than women)

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 Self-esteem (a person with low self-esteem is likely to
conform more)

 Familiarity of the individual with the subject matter (a
person is more likely to conform to the majority view if he
feels that he knows less about the subject matter than
they do)

 The expertise of the group members (if the individual
respects the group or perceives them to be very
knowledgeable he will be more likely to conform to their
views)

 The relationship between the individual and group
members (conformity increases if the individual knows
the other members of the group, i.e. it is a group of
peers)



Fig 3.1 An experiment to illustrate conformity


5.2 COUNTERING PEER PRES SURE AND CONFORMITY

The influence of peer pressure and conformity on an individual’s
views can be reduced considerably if the individual airs their
views publicly from the outset. However, this can be very
difficult: after Asch’s experiments, when asked, many
participants said they agreed with the majority as they did not
want to appear different or to look foolish.

Conformity is closely linked with ‘culture’ (described in the next
section). It is highly relevant in the aircraft maintenance
environment where it can work for or against a safety culture,
depending on the attitudes of the existing staff and their
influence over newcomers. In other words, it is important for an
organization to engender a positive approach to safety
throughout their workforce, so that peer pressure and
conformity perpetuates this. In this instance, peer pressure is
clearly a good thing. Too often, however, it works in reverse,
with safety standards gradually deteriorating as shift members
develop practices which might appear to them to be more
efficient, but which erode safety. These place pressure, albeit
possibly unwittingly, upon new engineers joining the shift, to do
likewise.

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SECTION 6: MOTIVATION

Motivated behaviour is goal-directed, purposeful behaviour, and
no human behaviour occurs without some kind of motivation
underpinning it. In aircraft maintenance, engineers are trained to
carry out the tasks within their remit. However, it is largely their
motivation which determines what they actually do in any given
situation. Thus, “motivation reflects the difference between what
a person can do and what he will do”.

Motivation is usually considered to be a positive rather than a
negative force in that it stimulates one to achieve various things.
However just because someone is motivated, this does not
mean to say that he is doing the right thing. Many Motivations
can be thought of as a basic human drive that arouses, directs
and sustains all human behaviour. Generally we say a person is
motivated if he is taking action to achieve something. Criminals
are highly motivated for instance. Motivation is difficult to
measure and predict. We are all motivated by different things,
for example, an artist might strive over many months to
complete a painting that he may never sell, whereas a
businessman may forfeit all family life in pursuit of financial
success.

With respect to aviation safety, being appropriately motivated is
vital. Ideally, aircraft maintenance engineers ought to be
motivated to work in a safe and efficient manner. However,
many factors may cause conflicting motivations to override this
ideal. For instance, the motivation of some financial bonus, or
de-motivation of working outdoors in extreme cold weather
might lead to less consideration of safety and increase the
likelihood of risk taking, corner cutting, violating procedures and
so on. Aircraft maintenance engineers should be aware of
conflicting motivations that impinge on their actions and attempt
to examine their motivations for working in a certain way.

6.1 MASLOW’S HIERARCHY O F NEEDS

Possibly one of the most well known theories which attempts to
describe human motivation is Maslow’s hierarchy of needs.
Maslow considered that humans are driven by two different sets
of motivational forces:

 Those that ensure survival by satisfying basic physical
and psychological needs
 Those that help us to realize our full potential in life
known as self-actualization needs (fulfilling ambitions,
etc.)

Figure shows the hypothetical hierarchical nature of the needs
we are motivated to satisfy. The theory is that the needs lower
down the hierarchy are more primitive or basic and must be
satisfied before we can be motivated by the higher needs. For
instance, you will probably find it harder to concentrate on the
information in this document if you are very hungry (as the lower
level physiological need to eat predominates over the higher
level cognitive need to gain knowledge). There are always
exceptions to this, such as the mountain climber who risks his
life in the name of adventure. The higher up the hierarchy one
goes, the more difficult it becomes to achieve the need. High
level needs are often long-term goals that have to be
accomplished in a series of steps.

An aircraft maintenance engineer will fulfil lower level needs by
earning money to buy food, pay for a home and support a
family. They may well be motivated by middle level needs in
their work context (e.g. social groups at work, gaining status
and recognition).

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It is noteworthy that for shift workers, tiredness may be a more
powerful motivator than a higher order need (such as personal
satisfaction to get the job done in time or accurately).

An interesting experiment on motivation was carried out in 1924
at the Hawthorne Works of the Western Electric Company in
Chicago. Here, the management altered various factors such as
rest periods, lighting levels, working hours, etc. and each time
they did so, performance improved, even when the apparent
improvements were taken away! This suggested that it was not
the improvements themselves which were causing the
increased production rates, but rather the fact that the staff felt
that management were taking notice of them and were
concerned for their welfare. This phenomenon is known as the
Hawthorne effect.

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Fig Maslow’s hierarchy of needs. Source: Maslow, 1954

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6.2 DE-MOTIVATION

Highly motivated people tend to show the following
characteristics:

 high performance and results being consistently
achieved

 the energy, enthusiasm and determination to succeed

 unstinting co-operation in overcoming problems

 willingness to accept responsibility

 willingness to accommodate change

People who are de-motivated lack motivation, either intrinsically
or through a failure of their management to motivate the staff
who works for them. De-motivated people tend to demonstrate
the following characteristics:
 apathy and indifference to the job, including reduced
regard for safety whilst working

 a poor record of time keeping and high absenteeism

 an exaggeration of the effects/difficulties encountered in
problems, disputes and grievances

 a lack of co-operation in dealing with problems or
difficulties

 unjustified resistance to change

However, care should be taken when associating these
characteristics with lack of motivation, since some could also be
signs of stress.

There is much debate as to the extent to which financial reward
is a motivator. There is a school of thought which suggests that
whilst lack of financial reward is a de-motivator, the reverse is
not necessarily true. The attraction of the extra pay offered to
work a ‘ghoster’1 can be a strong motivator for an individual to
ignore the dangers associated with working when tired.

The motivating effects of job security and the de-motivating
impact of lack of job security is also an area that causes much
debate. The ‘hire and fire’ attitude of some companies can,
potentially, be a major influence upon safety, with real or
perceived pressure upon individuals affecting their performance
and actions. It is important that maintenance engineers are
motivated by a desire to ensure safety (Maslow’s ‘self
esteem/self respect’), rather than by a fear of being punished
and losing their job (Maslow’s ‘security’). It is possible that the
“can do” culture, which is evident in some areas of the industry,
may be generated by the expectancy that if individuals do not
‘deliver’, they will be punished (or even dismissed) and,
conversely, those who do ‘deliver’ (whether strictly by the book
or not, finding ways around lack of time, spares or equipment)
are rewarded and promoted. This is not motivation in the true
sense but it has its roots in a complex series of pressures and
drives and is one of the major influences upon human
performance and human error in maintenance engineering.

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SECTION 7: CULTURE ISSUES

Disharmony in the workplace can arise through differences in
cultural background and can be the most difficult to rectify.
People tend to bring with them from childhood, deep-rooted
ideologies which will be hidden in day to day relationships.
When problems arise, losses of control lead to conflict which is
usually of the most disruptive kind, and the most difficult to deal
with.

People within a group, regarding each other as a member of the
group, see out of group members as different. The group will
categorise the differences with ‘out of group’ members and will
perceive the differences as being greater than they really are.
This categorisation leads to stereotyping where strong positive
or negative attitudes towards the ‘out group’ are being
developed.

Stereotyping has three main characteristics:

 People are categorised on the basis of very visible
characteristics e.g.:
o RACE
o SEX
o NATIONALITY
o BODY APPEARANCE
o DRESS
o DISABILITY, ETC.
 All members of a particular group are assumed to have
the same characteristics.

 Anybody who is seen to belong to a particular group will
therefore automatically be assumed to have the same
characteristics as the group.

Prejudice can be positive or negative in our attitude to a group.
If we treat a group badly because of our negative attitude we
are said to be discriminating against them.

Prejudice and Discrimination are caused by:

 Historical/Economic Causes
 Cultural Causes
 Situation (or Interpersonal) Causes
 Individual Causes

Historical Causes

Much of the discrimination against blacks and Asians can be
traced back to Britain’s colonial days; blacks were imported into
this country, and used in the colonies as slaves – and slaves by
definition do not have equal rights or fair treatment. The British
view of the inhabitants of its colonies was generally that they
were inferior to ‘true’ Britons intellectually, socially and often in
motivation. When workers were required, however, the colonies
provided a readily available (and cheap) supply. Marxist
sociologists see prejudice as a way in which the ruling classes
maintain the attitude within society that a particular group or
groups are in some way inferior, and therefore the ruling
classes are justified in exploiting either the group or its
resources.

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Cultural Causes

Changes in the ways in which society operates may produce
breeding grounds for racial prejudice. For example, increased
urbanisation (people being attracted to or forced to live in
towns), mechanisation and unemployment (and competition for
jobs), the increased importance of training and qualifications,
the increasing power of the media (so that people believe what
they are told, rather than developing their own internal
standards), changes in the structure of the family and in
standards of morality, and the upward mobility (improvement in
social position) of some groups are all thought by sociologists
and anthropologists to have increased the level of prejudice.

Social processes, such as the law and education, may help to
maintain prejudice by making formal the unequal treatment of
particular groups. Because people and groups become crowded
together, they are in competition for work and they are more
easily affected by the media.

Situational and Interpersonal Causes

Situational causes of prejudice include conformity to group
norms – i.e. people do not like being the odd one out in a group.
If the group have a prejudiced attitude, the non-prejudiced
member will conform and behave in prejudiced ways. In the
Southern States of the USA in the 1960s, restaurant owners
often used the ‘I’m not prejudiced, but my customers’ wouldn’t
like it’ excuse as a reason for their refusal to admit blacks.
However as situations change so do many prejudices.

Individual Causes

There are two main theories to explain why prejudice occurs in
individuals. The first is the frustration/aggression hypothesis.
The idea is that, if a person is prevented from reaching a goal or
has something they want taken away, they will experience an
increase in aggression. If the original source of frustration is not
attackable, the aggression is redirected on to a ‘scapegoat’.
The second theory of individual prejudice takes the view that
there are people, who, because of some flaw in their
personality, become prejudiced. There are many theories for
this prejudice, such as a strict, rigid and punishment centred
discipline in a child’s upbringing, with parents they think of as
wholly good, but who are, in fact, deeply prejudiced.

Prejudice can lead to HARASSMENT in the workplace causing
stress to the individual. It can be in the form of touching and
bodily contact, the spoken word, the written word, drawings and
gestures. Where any of these become a nuisance, management
should help the individual to tackle the problem.

7.1 SUMMARY

The answer is to have well motivated groups of internationalist,
non-judgemental people, working in perfect conditions and
nothing ever going wrong. But of course this cannot be, we
have to make allowances for one another and accept that, as
aircraft engineers, our first priority is to the job in hand and to
the aircraft’s safety.

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Human Factors
Chapter 4
FACTORS AFFECTING PERFORMANCE

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Contents

SECTION 1: FITNESS AND HEALTH ------------------------------------------ 1
1.1 PRE-EMPLOYMENT DISPOSITION -------------------------------------- 1
1.2 DAY-TO-DAY FITNESS AND HEALTH ----------------------------------- 1
1.3 POSITIVE MEASURES ------------------------------------------------------ 3
SECTION 2: STRESS: DOMESTIC AND WORK RELATED ----------------- 4
2.1 CAUSES AND SYMPTOMS ------------------------------------------------ 4
2.1 DOMESTIC STRESS --------------------------------------------------------- 5
2.3 WORK RELATED STRESS -------------------------------------------------- 5
2.4 STRESS MANAGEMENT --------------------------------------------------- 5
2.5 ATTENTION/MOTIVATION/PERFORMANCE ------------------------- 6
LOW AROUSAL ----------------------------------------------------------------- 7
OPTIMAL AROUSAL ----------------------------------------------------------- 7
HIGH AROUSAL ----------------------------------------------------------------- 7
SYMPATHETIC SYSTEM ------------------------------------------------------- 7
PARASYMPATHETIC SYSTEM ------------------------------------------------ 7
2.6 Environmental/Physical Stress ------------------------------------------ 8
TEMPERATURE ----------------------------------------------------------------- 8
NOISE ----------------------------------------------------------------------------- 8
STRESS---------------------------------------------------------------------------- 9
2.7 THE POSSIBLE EFFECTS OF STRESS ------------------------------------ 12

SECION 3: TIME PRESSURE AND DEADLINES --------------------------- 13
3.1 THE EFFECTS OF TIME PRESSURE AND DEADLINES -------------- 13
3.2 MANAGING TIME PRESSURE AND DEADLINES -------------------- 14
SECTION 4: WORKLOAD ----------------------------------------------------- 15
4.1 AROUSAL ------------------------------------------------------------------- 15
4.2 FACTORS DETERMINING WORKLOAD ------------------------------- 17
section 5: SLEEP AND FATIGUE, SHIFTWORK --------------------------- 18
circadian rhythm of body temperature ---------------------------------- 19
5.1 Sleep Disorders ----------------------------------------------------------- 24
section 6: ALCOHOLISM, MEDICATION AND DRUG ABUSE --------- 26

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SECTION 1: FITNESS AND HEALTH

The job of an aircraft maintenance engineer can be physically
demanding. In addition, his work may have to be carried out in
widely varying physical environments, including cramped
spaces, extremes of temperature, etc. There are at present no
defined requirements for physical or mental fitness for
engineers or maintenance staff. ICAO Annex 11 states:

“An applicant shall, before being issued with any licence or
rating [for personnel other than flight crew members], meet such
requirements in respect of age, knowledge, experience and,
where appropriate, medical fitness and skill, as specified for that
licence or rating.”

In the UK, the ICAO requirements are enforced through the
provision of Article 13 (paragraph 7) of the Air Navigation order
(ANO). This state:

“The holder of an aircraft maintenance engineer’s license shall
not exercise the privileges of such a license if he knows or
suspects that his physical or mental condition renders him unfit
to exercise such privileges.”

There are two aspects to fitness and health: the disposition of
the engineer prior to taking on employment and the day-to-day
well being of the engineer once employed.

1.1 PRE-EMPLOYMENT DISPOSITI ON

Some employers may require a medical upon commencement
of employment. This allows them to judge the fitness and health
of an applicant (and this may also satisfy some pension or
insurance related need). There is an obvious effect upon an
engineer’s ability to perform maintenance or carry out
inspections if through poor physical fitness or health he is
constrained in some way (such as his freedom of movement, or
his sight). In addition, an airworthiness authority, when
considering issuing a licence, will consider these factors and
may judge the condition to be of such significance that a licence
could not be issued. This would not, however, affect the
individual’s possibility of obtaining employment in an alternative
post within the industry where fitness and health requirements
are less stringent.

1.2 DAY-TO-DAY FITNESS AND HEALTH

Fitness and health can have a significant effect upon job
performance (both physical and cognitive). Day-to-day fitness
and health can be reduced through illness (physical or mental)
or injury.

Responsibility falls upon the individual aircraft maintenance
engineer to determine whether he is not well enough to work on
a particular day. Alternatively, his colleagues or supervisor may
persuade or advise him to absent himself until he feels better. In
fact, as the CAA’s Airworthiness Notice No. 47 (AWN47)1
points out; it is a legal requirement for aircraft maintenance
engineers to make sure they are fit for work:

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“Fitness: In most professions there is a duty of care by the
individual to assess his or her own fitness to carry out
professional duties. This has been a legal requirement for some
time for doctors, flight crew members and air traffic controllers.
Licensed aircraft maintenance engineers are also now required
by law to take a similar professional attitude. Cases of subtle
physical or mental illness may not always be apparent to the
individual but as engineers often work as a member of a team
any substandard performance or unusual behaviour should be
quickly noticed by colleagues or supervisors who should notify
management so that appropriate support and counselling action
can be taken.”

Many conditions can impact on the health and fitness of an
engineer and there is not space here to offer a complete list.
However, such a list would include:

 Minor physical illness (such as colds, ‘flu, etc.)

 More major physical illness (such as HIV, malaria, etc.)

 Mental illness (such as depression, etc.)

 Minor injury (such as a sprained wrist, etc.)

 Major injury (such as a broken arm, etc.)

 Ongoing deterioration in physical condition possibly
associated with the ageing process (such as hearing
loss, visual defects, obesity, heart problems, etc.

 Affects of toxins and other foreign substances (such as
carbon monoxide poisoning, alcohol, illicit drugs, etc.)

‘Unfit for work’ is a complex issue dependent upon the nature of
the illness or condition, its effect upon the individual, the type of
work to be done, environmental conditions, etc. Instead, it is
important that the engineer is aware that his performance, and
consequently the safety of aircraft he works on, might be
affected adversely by illness or lack of fitness.

An engineer may consider that he is letting down his colleagues
by not going to work through illness, especially if there are
ongoing manpower shortages. However, he should remind
himself that, in theory, management should generally allow for
contingency for illness. Hence the burden should not be placed
upon an individual to turn up to work when unfit if no such
contingency is available. Also, if the individual has a contagious
illness (e.g. ‘flu), he may pass this on to his colleagues if he
does not absent himself from work and worsen the manpower
problem in the long run. There can be a particular problem with
some contract staff due to loss of earnings or even loss of
contract if absent from work due to illness. They may be
tempted to disguise their illness, or may not wish to admit to
themselves or others that they are ill. This is of course
irresponsible, as the illness may well adversely affect the
contractor’s standard of work.

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1.3 POSITIVE MEASURES

Aircraft maintenance engineers can take common sense steps
to maintain their fitness and health. These include:

 Eating regular meals and a well-balanced diet

 Taking regular exercise (exercise sufficient to double the
resting pulse rate for 20 minutes, three times a week is
often recommended)

 Stopping smoking

 Sensible alcohol intake (for men, this is no more than 3 -
4 units a day or 28 per week, where a unit is equivalent
to half a pint of beer or a glass of wine or spirit)

Finally, day-to-day health and fitness can be influenced by the
use of medication, alcohol and illicit drugs.

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SECTION 2: STRESS: DOMESTIC AND WORK REL ATED

Stress is an inescapable part of life for all of us. From a human
viewpoint, stress results from the imposition of any demand or
set of demands which require us to react, adapt or behave in a
particular manner in order to cope with or satisfy them. Up to a
point, such demands are stimulating and useful, but if the
demands are beyond our personal capacity to deal with them,
the resulting stress is a problem.

Stress can be defined as any force, that when applied to a
system, causes some significant modification of its form, where
forces can be physical psychological or due to social pressures.

2.1 CAUSES AND SYMPTOMS

Stress is usually something experienced due to the presence of
some form of stressor, which might be a one-off stimulus (such
as a challenging problem or a punch on the nose), or an on-
going factor (such as an extremely hot hangar or an
acrimonious divorce). From these, we get acute stress (typically
intense but of short duration) and chronic stress (frequent
recurrence or of long duration) respectively.

Different stressors affect different people to varying extents.
Stressors may be:

 Physical - such as heat, cold, noise, vibration, presence
of something damaging to health (e.g. carbon monoxide)
 Psychological - such as emotional upset (e.g. due to
bereavements, domestic problems, etc.), worries about
real or imagined problems (e.g. due to financial
problems, ill health, etc.)

 Reactive - such as events occurring in everyday life (e.g.
working under time pressure, encountering unexpected
situations, etc.)

“A stress problem can manifest itself by signs of irritability,
forgetfulness, and sickness absence, mistakes, or alcohol or
drug abuse. Management has a duty to identify individuals who
may be suffering from stress and to minimize workplace
stresses. Individual cases can be helped by sympathetic and
skilful counselling which allows a return to effective work and
licensed duties.”

In brief, the possible signs of stress can include:

 Physiological symptoms - such as sweating, dryness of
the mouth, etc.

 Health effects - such as nausea, headaches, sleep
problems, diarrhoea, ulcers, etc.

 Behavioural symptoms - such as restlessness, shaking,
nervous laughter, taking longer over tasks, changes to
appetite, excessive drinking, etc.

 Cognitive effects - such as poor concentration,
indecision, forgetfulness, etc.

 Subjective effects - such as anxiety, irritability,
depression, moodiness, aggression, etc.

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2.1 DOMESTIC STRESS

When aircraft maintenance engineers go to work, they cannot
leave stresses associated with home behind. Pre-occupation
with a source of domestic stress can play on one’s mind during
the working day, distracting from the working task. Inability to
concentrate fully may impact on the engineer’s task
performance and ability to pay due attention to safety.

Domestic stress typically results from major life changes at
home, such as marriage, birth of a child, a son or daughter
leaving home, bereavement of a close family member or friend,
marital problems, or divorce. It should be noted that individuals
respond to stressful situations in very different ways. Generally
speaking though, people tend to regard situations with negative
consequences as being more stressful than when the outcome
of the stress will be positive (e.g. the difference between being
made redundant from work and being present at the birth of a
son or daughter).

2.3 WORK RELATED STRESS

Aircraft maintenance engineers can experience stress for two
reasons at work: because of the task or job they are
undertaking at that moment, or because of the general
organizational environment. Stress can be felt when carrying
out certain tasks that are particularly challenging or difficult. This
stress can be increased by lack of guidance in this situation, or
time pressures to complete the task or job (covered later in this
chapter). This type of stress can be reduced by careful
management, good training, etc.

Within the organization, the social and managerial aspects of
work can be stressful. Earlier we discussed the impact on the
individual of peer pressure, organizational culture and
management, all of which can be stressors. In the commercial
world that aircraft maintenance engineers work in, shift patterns,
lack of control over own workload, company reorganization and
job uncertainty can also be sources of stress.

2.4 STRESS MANAGEMENT

Once we become aware of stress, we generally respond to it by
using one of two strategies: defence or coping. Coping
strategies involve dealing with the source of the stress rather
than just the symptoms (e.g. delegating workload, prioritizing
tasks, sorting out the problem, etc.). Unfortunately, it is not
always possible to deal with the problem if this is outside the
control of the individual (such as during an emergency), but
there are well-published techniques for helping individuals to
cope with stress2. Good stress management techniques
include:

 Relaxation techniques

 Careful regulation of sleep and diet

 A regime of regular physical exercise

 Counselling - ranging from talking to a supportive friend
or colleague to seeking professional advice

There is no magic formula to cure stress and anxiety, merely
common sense and practical advice.

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2.5 ATTENTION/MOTIVATION /PERFORMANCE

As has been indicated, stress can have a positive as well as a
negative effect. Just how well you carry out a task depends on
your arousal state. This is shown in the inverted U curve on the
figure below.





























STRESS VERSUS PERFORMANCE

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LOW AROUSAL In this state the individual is not expecting
any difficult tasks to perform. Motivation is
low and processing of information can be
very low. The attention is generally dull.
Performance capability is low because it
might not matter too much if anything does
not get done.

OPTIMAL
AROUSAL
At optimal arousal we are at our most
efficient. We have enough demands to
keep our attention and to be alert. We
have the capability to deal with complex
tasks.

HIGH AROUSAL In this state our performance starts to
deteriorate, errors are made and
information may be missed. We may feel
we are being overloaded with tasks and
suffering from a narrowing of attention as
we tend to focus on a limited number of
tasks. We may become emotionally
disturbed.

The arousal mechanism operates through the AUTONOMIC
NERVOUS SYSTEM which controls the body’s vital functions,
over which we have no conscious control. This system is
divided into the SYMPATHETIC and PARASYMPATHETIC
systems.

SYMPATHETIC
SYSTEM
This provides the body with the
ability/resources to cope with new and
sudden sources of stress, possibly to fight
or run away. This system prepares us for
physical activity for survival.
PARASYMPATH
ETIC SYSTEM
This system restores the body to normal
functioning when the stress has abated.

The Physiological Responses to Stress

 The pupils of the eye dilate.
 The flow of saliva is inhibited.
 The heartbeat rate will increase.
 The bronchi in the lungs dilate.
 Adrenalin will be secreted.
 Glycogen will be released into the blood.
 Bladder contraction will be inhibited.
 Peristalsis (muscle contractions in the gullet) will be
inhibited.

The body has prepared itself, giving increased supply of energy
to the muscles ready for flight or fight. The above reactions can
occur without the actual occurrence of the event. Anticipation of
the perceived demand or threat is enough to trigger the
responses. These triggers of stress can have mental and
environmental causes. Repeated exposure to moderate levels
of stress from the environment causes the body to adapt to
reduce the impact of the stress. For example, if an individual
lives close to a busy railway line the noise of the passing trains
will not be noticed after a time. But a visitor would certainly
notice the high sound levels.

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2.6 ENVIRONMENTAL/PHYSIC AL STRESS

TEMPERATURE A comfortable temperature for most people
in normal clothing is 20C.

Above 30C the heart rate, blood pressure
and sweating increases. Attention becomes
restricted or focused.

Below 15C the individual becomes
uncomfortable and falling temperatures may
cause some loss of feeling and some
control in the hands, especially for fine
muscle movement and control.

NOISE In low arousal states some noise can
improve performance towards the optimum,
preventing boredom and fatigue. Excessive
noise will disrupt performance and will
cause annoyance and irritability. The heart
rate might go up. Loss of attention and
focusing of attention can also occur.

VIBRATION

Vibration at various frequencies and
intensity can have effects on the human
beings vision and motor performance.

1 to 4 Hz Interferes with breathing

4 to 10 Hz Can cause chest and
abdominal pains


8 to 12 Hz Will cause back ache

10 to 20 Hz Causes headache, eyestrain,
pains in the throat, speech
difficulties and muscular
tensions.

Perhaps this is why helicopter flight is tiring
and stressful.

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STRESS

Death of spouse or partner .......................................................................................... 100
Divorce .......................................................................................................................... 73
Marital separation .......................................................................................................... 65
Death of close family member ....................................................................................... 63
Personal injury or illness ................................................................................................ 53
Marriage ........................................................................................................................ 50
Loss of job ..................................................................................................................... 47
Marital reconciliation ...................................................................................................... 45
Retirement ..................................................................................................................... 45
Change in health of family member ............................................................................... 44
Pregnancy ..................................................................................................................... 40
Sexual problems ............................................................................................................ 39
Addition of new family member ...................................................................................... 39
Death of close friend ..................................................................................................... 37
Change to different kind of work .................................................................................... 36
Taking on a large mortgage ........................................................................................... 31
Change in responsibilities at work ................................................................................. 29
Son or daughter leaving home ....................................................................................... 29
Wife starts/stops work ................................................................................................... 26
Starting or leaving a course ........................................................................................... 26
Trouble with the boss .................................................................................................... 23
Change in residence ..................................................................................................... 20
Taking on a bank loan or HP debt ................................................................................. 17
Change in eating habits ................................................................................................. 15
Vacation ........................................................................................................................ 13
Christmas ...................................................................................................................... 12
Minor violations of law ................................................................................................... 11

Scoring



Below 60 : a life unusually free of stress
60 – 80: normal amount of stress
80 – 100: stress in life is rather high
100 +: under serious amount of stress

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Humidity

For comfort the human being requires a relative humidity level
of 40-60%. At low humidity levels the individual becomes
uncomfortable due to drying out of the mucous membranes of
the nose and throat. Eyes become sore and tears evaporate
rapidly. This state can occur if humidity is not controlled in
pressurised high flying aircraft.

High humidity makes the individual feel uncomfortable and
reluctant to continue physical effort. The body has difficulty in
cooling by sweating.

Domestic Stress

The domestic environment also has its stresses. We may have
emotional problems in our relationships with spouses and
immediate family. This can be due to sex, money, health
worries and housing problems. There are many other examples
that can raise the individual’s overall stress levels. From the
table of stress we can see bereavement of a partner is placed at
100. When a person is under such stress his performance and
reactions are severely degraded and therefore he should not be
asked to perform his duties until he feels able to perform
normally.

Work Stress

Stress in the work place may arise from a high work load
constantly taken by an individual. This may be a load placed
upon him by management over a long period of time or a total
overload in a shorter period.

The load affecting his performance, as previously discussed in
arousal levels, by being focused on a narrow track of tasks and
not perceiving the problems in those he might be neglecting.
The physical environment of the workplace will affect the
engineers performance ie temperature, noise, etc. There may
be hazards in the workplace from dust, chemicals, working at
height which will increase your awareness levels and lead to
stress.

We may feel the job is boring, repetitive or there is too little to
do. We may feel that we do not have the necessary knowledge
and skill to carry out the task which will make us feel stressed.

If management exert pressure on its employees to operate in
ways that are more consistent with short term monetary gains
than with safety and good engineering practice then the whole
company will develop ORGANISATIONAL STRESS. This will
be demonstrated by staff illness, poor industrial relations,
absenteeism and probably a high accident and incident rate.
This will be very costly in the long term.

In the workplace we will meet poor relations with management
and fellow work mates. This could be the result of a poor
management system within the company, but bullying, racial
and sexual harassment may be met on the shop floor. The
individual might be physically handicapped or have poor motor
skills, hearing or sight. The engineer might have a ‘can do’
attitude and inadvertently overload himself, stressing himself
unnecessarily.

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Effects of Stress on Health

Previously in the notes on arousal we saw the Physiological
Responses to Stress ie high blood pressure, sweating, etc.
These effects in the long term affect the individuals health. The
earliest physical signs are seen in the gastro intestinal system.
Maybe starting with indigestion, nausea, diarrhoea leading in
time to ulcers in the stomach. There is evidence of a
connection between permanently raised blood pressure and
coronary heart disease leading to heart attacks and strokes.

People under stress will have a higher incidence of asthma,
headaches, sleep disorders and neuroses. They are also more
susceptible to colds and influenza.

Signs of Stress

When under stress the individual may show outward signs by
being restless, perhaps trembling and laughing nervously. His
behaviour may become impulsive and excitable. However, he
may take longer over normal routine tasks. There may be a
change in his smoking and drinking habits. He will be more
likely to have an accident himself. As we have seen previously,
when stressed, our thought process is affected and we become
forgetful. The ability to concentrate is reduced; the ability to
prioritise and make decisions is also affected.

The individual will feel anxious and may show signs of
aggression. Mood swings may lead to apathy, fatigue and low
self-esteem. The signs of aggression will be irritability, threat
and bad temper.

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2.7 THE
POSSIBLE
EFFECTS OF
STRESS




PHYSIOLOGICAL
Increased blood sugar levels
Increased heart rate
High blood pressure
Dryness of mouth
Sweating
Dilation of pupils
Difficulty in breathing
Hot/cold spells
A ‘lump in the throat’
Numbness
Tingling in the limbs
COGNITIVE (Thought Process)
Inability to determine priorities and to
make decisions
Lack of concentration
Forgetfulness
Hypersensitivity to criticism
Mental blocks
Difficulty in switching off
SUBJECTIVE (Feeling)
Anxiety
Aggression
Apathy
Boredom
Depression
Fatigue
Frustration
Guilt/shame
Irritability/bad temper
Low self-esteem
Moodiness
Threat/tension
Nervousness
Loneliness
BEHAVIOURAL
Accident, proneness
Drug taking
Emotional outbursts
Excessive eating of appetite
Excessive drinking/smoking
Excitability
Impulsive behaviour
Impaired speech
Nervous laughter
Restlessness
Trembling
Taking longer over tasks (add
from other table)
ORGANISATIONAL
Absenteeism
Poor industrial relations
Poor productivity
High accident rate
High labour turnover
Poor organisational climate
Antagonism at work
Job dissatisfaction
SUBJECTIVE (Feelings)
Tenseness
Explosive changes in mood
Impulsiveness
Frustration over failure get results
Anger, irritability, bitterness,
resentment
Self-condemnation and guilt
Unease, panic feeling, general
anxiety
Hopelessness and sadness
HEALTH
Asthma
Coronary heart disease
Ulcers
Nausea
Chest/back pains
Diarrhoea/constipation
Faintness/dizziness
Dyspepsia (indigestion/colic)
Skin rashes
Frequent urination
Headaches/migraines
Neuroses
Insomnia
Psychosomatic disorders
Diabetes
Loss of sexual interest
Weakness
Phobias (exaggerated fears)
Hypertension (high blood
pressure)
Hair loss
Cancer
Allergies
Sleep disorders
Skin disorders
Sexual disorders
Common cold and flu

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SECION 3: TIME PRESSURE AND DEADLINES

There is probably no industry in the commercial environment
that does not impose some form of deadline, and consequently
time pressure, on its employees. Aircraft maintenance is no
exception. It was highlighted in the previous section that one of
the potential stressors in maintenance is time pressure. This
might be actual pressure where clearly specified deadlines are
imposed by an external source (e.g. m anagement or
supervisors) and passed on to engineers, or perceived where
engineers feel that there are time pressures when carrying out
tasks, even when no definitive deadlines have been set in
stone. In addition, time pressure may be self-imposed, in which
case engineers set themselves deadlines to complete work (e.g.
completing a task before a break or before the end of a shift).

Management has contractual pressures associated with
ensuring an aircraft is released to service within the time frame
specified by their customers. Striving for higher aircraft
utilization means that more maintenance must be accomplished
in fewer hours, with these hours frequently being at night.
Failure to do so can impact on flight punctuality and passenger
satisfaction. Thus, aircraft maintenance engineers have two
driving forces: the deadlines handed down to them and their
responsibilities to carry out a safe job. The potential conflict
between these two driving pressures can cause problems.

3.1 THE EFFECTS OF TIME PRESSURE AND DEADLIN ES

As with stress, it is generally thought that some time pressure is
stimulating and may actually improve task performance.
However, it is almost certainly true that excessive time pressure
(actual or perceived, external or self-imposed), is likely to mean


that due care and attention when carrying out tasks diminishes
and more errors will be made. Ultimately, these errors can lead
to aircraft incidents and accidents.

It is possible that perceived time pressure would appear to have
been a contributory factor in the BAC 1-11 accident described in
Chapter 1. Although the aircraft was not required the following
morning for operational use, it was booked for a wash. The
wash team had been booked the previous week and an aircraft
had not been ready. This would have happened again, due to
short-staffing, so the Shift Manager decided to carry out the
windscreen replacement task himself so that the aircraft would
be ready in time.

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3.2 MANAGING TIME PRESSU RE AND DEADLINES

One potential method of managing time pressures exerted on
engineers is through regulation. For example, FAA research has
highlighted the need to insulate aircraft maintenance engineers
from commercial pressures. They consider this would help to
ensure that airworthiness issues will always take precedence
over commercial and time pressures. Time pressures can make
‘corner-cutting’ a cultural norm in an organization. Sometimes,
only an incident or accident reveals such norms (the extract
from the Aloha accident above exemplifies this).

Those responsible for setting deadlines and allocating tasks
should consider:

 Prioritizing various pieces of work that need to be done

 The actual time available to carry out work (considering
breaks, shift handovers etc.)

 The personnel available throughout the whole job
(allowing a contingency for illness)

 The most appropriate utilization of staff (considering an
engineer’s specialization, and strengths and limitations)

 Availability of parts and spares

An extract from the NTSB report on the Aloha accident refers to
time pressure as a possible contributory factor in the accident:

“The majority of Aloha's maintenance was normally conducted
only during the night. It was considered important that the
airplanes be available again for the next day's flying schedule.
Such aircraft utilization tends to drive the scheduling, and
indeed, the completion of required maintenance work.
Mechanics and inspectors are forced to perform under time
pressure. Further, the intense effort to keep the airplanes flying
may have been so strong that the maintenance personnel were
reluctant to keep airplanes in the hangar any longer than
absolutely necessary.”

It is important that engineering staff at all levels are not afraid to
voice concerns over inappropriate deadlines, and if necessary,
cite the need to do a safe job to support this. As highlighted
earlier, within aircraft maintenance, responsibility should be
spread across all those who play a part. Thus, the aircraft
maintenance engineer should not feel that the ‘buck stops here’.

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SECTION 4: WORKLOAD

The preceding sections on stress and time pressure have both
indicated that a certain amount of stimulation is beneficial to an
aircraft maintenance engineer, but that too much stimulation
can lead to stress or over-commitment in terms of time. It is
noteworthy that too little stimulation can also be a problem.

Before going on to discuss workload, it is important to consider
this optimum level of stimulation or arousal.

4.1 AROUSAL

Arousal in its most general sense refers to readiness of a
person for performing work. To achieve an optimum level of
task performance, it is necessary to have a certain level of
stimulation or arousal. This level of stimulation or arousal varies
from person to person. There are people who are overloaded by
having to do more than one task at a time; on the other hand
there are people who appear to thrive on stress, being happy to
take on more and more work or challenges. Figure 3.1 shows
the general relationship between arousal and task performance.

At low levels of arousal, our attention mechanisms will not be
particularly active and our performance capability will be low
(complacency and boredom can result). At the other end of the
curve, performance deteriorates when arousal becomes too
high. To a certain extent, this is because we are forced to shed
tasks and focus on key information only (called narrowing of
attention). Best task performance occurs somewhere in the
middle. In the work place, arousal is mainly influenced by
stimulation due to work tasks.

However, surrounding environmental factors such as noise may
also influence the level of arousal.

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Fig 3.1 Optimum arousal leads to best task performance (adapted from Thom 1999)

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4.2 FACTORS DETERMINING WORKLOAD

An individual aircraft maintenance engineer can usually identify
what work he has to do quite easily. It is more difficult to assess
how that work translates into workload.

The degree of stimulation exerted on an individual caused by a
task is generally referred to as workload, and can be separated
into physical workload and mental workload.

As noted in the section on information processing earlier,
humans have limited mental capacity to deal with information.
We are also limited physically, in terms of visual acuity,
strength, dexterity and so on. Thus, workload reflects the
degree to which the demands of the work we have to do eat into
our mental and physical capacities. Workload is subjective (i.e.
experienced differently by different people) and is affected by:

 The nature of the task, such as the

 Physical demands it requires (e.g. Strength
required, etc.)

 Mental demands it requires (e.g. complexity of
decisions to be made, etc.).








 The circumstances under which the task is performed,
such as the

 Standard of performance required (i.e. degree of
accuracy)

 Time available to accomplish the task (and thus
the speed at which the task must be carried out)

 Requirement to carry out the task at the same
time as doing something else

 Perceived control of the task (i.e. is it imposed by
others or under your control, etc.)

 Environmental factors existing at time (e.g.
extremes of temperature, etc.)

 The person and his state, such as his:

 Skills (both physical and mental)

 His experience (particularly familiarity with the
task in question)

 His current health and fitness levels

 His emotional state (e.g. stress level, mood, etc.)

As the workload of the engineer may vary, he may experience
periods of overload and under-load. This is a particular feature
of some areas of the industry such as line maintenance.

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SECTION 5: SLEEP AND FATIGUE, SHIFTWORK

Sleep is essential to a human’s well being. Not achieving
enough sleep of the right type will result in the person feeling
fatigue. For man, sleep is usually around 8 hours in every 24
hours, though some people will need more and others less.
During sleep the body is recuperating from the physical activity
of the day and may be essential for mental well being, by
ongoing mental processes whilst asleep.

Sleep has a particular cycle during each sleep period, varying
from drowsiness, light sleep, deep sleep through to rapid eye
movement (REM) sleep. The duration of sleep depends on our
internal body rhythm, but often is affected by outside influences,
i.e. alarm clocks.

Biological Clocks

The physiological processes in the body undergo rhythmic
fluctuations and they occur whether the person is awake or
asleep. One of the rhythms that affect man and animals has
periodicities of about 24 hours. These are known as
CIRCADIAN RHYTHMS, from the Latin CIRCA (about) and
DIES (day).

In normal conditions our circadian rhythms are locked to 24
hours by external time cues such as light and darkness or by
social activities such as meal times. The greatest cues of all
are provided by clock times but other external events, such as
increase in traffic noise at certain times, assist in the regulation
of our internal biological clock. These cues are known as
‘Zeitgebers’ (German for ‘time givers’).

If an individual is isolated from these zeitgebers, no clocks, no
set meal times, or no way of detecting light changes, the
circadian rhythms will ‘free run’ to a periodicity of about 25
hours. This means that an average individual isolated from
these cues will, instead of working to an average 16 hours
awake, 8 hours sleep, extend his day to 17 hours awake, 8
hours sleep.

These internal rhythms affect the modern air traveller. An
individual may cross several time zones in a very short time.
This leads to a discrepancy between the local time at the
destination and the body time of the traveller.

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Body Temperature

The sleep/wake cycle and the body temperature cycle run
together. The highest temperature occurs around 1800 hours
and the lowest at 0500 hours. When the body temperature is at
its lowest we find it very hard to stay awake. We will feel
drowsy when the temperature is falling and the most wide
awake when the temperature is rising. This may also be why
we have difficulty sleeping after crossing time zones resulting in
fatigue (Jet Lag). The temperature rhythm is unaffected even if
sleep is not taken during this period.



circadian rhythm of body temperature




Sleep Credit/Debit

The sleep/awake system is often considered as a credit/debit
system, where an 8 hour sleep (credit) allows for a 16 hour
active period (debit). In simple terms it should mean1 hour of
sleep can credit the body with 2 hours of waking time.
However, a sleep of 10 to 12 hours after a long period of
strenuous activity will still only credit the body with 8 hours and
the individual will feel sleepy again after 16 hours. Sleep cannot
be stored in anticipation of a long period of waking ie a long shift
period.

But, the less sleep credits you have, the readier you are to
sleep. A gradual loss of sleeping time ie late working will result
in a cumulative sleep debit.

Also we cannot use our 8 hours credit to recharge our system at
any time during the 24 hours. From our circadian rhythm, sleep
is best taken when our temperature is falling and it will be more
refreshing than sleep taken when the body temperature is
rising. However a ‘nap’ will help the body to be in credit – ie a
small charge up.

When the work/sleep pattern matches the circadian rhythm then
all is well. But difficulties arise when shift patterns put the body
out of phase with the rhythms. The body in the small hours
feels that it should be asleep yet you have to work on until 6.00
am from 6.00 pm the previous evening. Some people on
regular night shifts may be able to re-synchronise; but others
may stay de-synchronised indefinitely.

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Shift Work

The effect of shift working on the shift engineers is a problem
that management have to address. Shift rotation, if practised,
does not improve the situation but after a break of a day or two
on dayshifts (8.00 am to 5.00 pm) the shift is moved forward
(midnight to 8.00 am) or backwards (5.00 pm to midnight).
Moving the shift backwards is most preferred as it follows the
body’s natural circadian rhythm to free run when there are no
time cues. Compressed shift patterns might be used. This is
where a normal weeks work is compressed into fewer days.
For example 4 days of 10 to 12 hour shifts followed by 3 days
off.

Time of Day and Performance

Performance on different tasks is affected differently by the time
of day. Performance improves as temperature increases and
declines as the temperature peaks and decreases. Short term
memory tasks decline throughout the day. Verbal reasoning
and mental arithmetic skills are best around midday. When
body temperature is low, reaction times, vigilance, and manual
dexterity are all affected. Early morning accidents were
Chernobyl, 3 mile Island, Challenger and the windscreen of the
BAC 1-11 was fitted in the period 0300-0500 hours the night
before the accident.

Driving accidents have also been statistically examined and a
peak of accidents has been noted around 1500 hours, possibly
due to overconfidence due to the height of the circadian rhythm
but other factors could affect the results.


Dangers of Sleep Deprivation

There are physical dangers associated with a lack of sleep.
Research conducted by the University of South Australia has
determined that the body reaction times slow down appreciably
when volunteers were deprived of sleep. When the body is 2
hours in deficit of sleep, the body reaction times are similar to
those experienced after drinking one pint of beer.

Consequently, a sleep debit of 4 hours giving a body reaction
time equivalent to drinking 2 pints of beer would impair the body
to the extent that would make it dangerous to drive, as you
would not be able to react sufficiently quickly in a dangerous
situation.

Sleep Phases

The human nervous system is capable of a wide range of
normal activity levels extending from deep sleep to extreme
anxiety or nervousness. These levels are called arousal levels
or levels of consciousness and are characterised by different
patterns in the electrical activity of the brain cells. Recordings
of the brain are called electroencephalograms (EEGs). In
experiments on sleep, eye movement is measured by an
electroculogram (EOG) and an electromyogram (EMG)
measures muscle tension or relaxation.

When the individual is awake with eyes open the EEG wave
pattern is characterised by rapid low amplitude oscillates
approaching 20Hz. These are known as beta waves. When
you close your eyes in a restful state the EEG trace of
approximately 10 Hz is produced and is known as an alpha
wave.

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As time passes you enter a phase of drowsiness (quiet
relaxation), sleep deepens you pass into light and deep sleep.
In deep sleep a delta wave is recorded on the EEG this is
known as slow wave sleep.

The various states of sleep have been classified in 5 stages.
Stage 1 is the transitional phase from waking and sleeping.
Stage 3 and 4 will be light to deep sleep.

The fifth stage of sleep is called Rapid Eye Movement or REM
sleep.

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Nerve cells in the brain do not rest during sleep; instead, they
carry out activities that are different from those of the waking
hours. Distinctive patterns of non-rapid eye movement (NREM)
as well as rapid eye movement (REM) sleep, when most
dreams occur, can be detected by recording the electrical
activity of the brain (shown right).

In this stage rapid eye movement is detected and the EEG
detects irregular activity. The EEG trace is similar to that of an
individual who is fully awake, whilst other measurements, such
as muscle activity show the individual to be certainly asleep.
Hence another name for REM sleep is Paradoxical sleep. REM
sleep is neither deeper nor shallower than the other stages; it is
a different kind of sleep. REM sleep is associated with
particular types of dreams, complex, bizarre, and emotionally
coloured. Dreams do occur in other sleep stages and if
awakened from slow wave sleep the individual will recall
feelings of choking or being crushed.

During any normal night’s sleep the sleep pattern operates on
an approximate 90 minutes cycle. In early sleep one passes
through about 10 minutes of stage 1, then about 15 minutes of
stage 2 before passing on to stages 3 and 4.

At the later stages of the first 90 minutes cycle the first REM
stage occurs but this first REM experience lasts only 10 to 20
minutes before the person passes back into slow wave sleep.
After the second cycles of 90 minutes there is usually no slower
wave sleep. About 50% of our total sleep is stage 2 sleep.
Later in the sleep pattern the duration of REM sleeps period’s
increases.


A sleep profile for a typical night’s sleep is shown in the
diagram. The individual stages will vary depending on the
activities prior to sleep.

Slow wave sleep is believed to be necessary for body tissue
restoration while REM sleep may be for organising the memory.
After strenuous physical activity your body will need more slow
wave sleep. After a period of learning it has been observed that
there is an increase in REM sleep. If a person is deprived of
either slow wave or REM sleep, there will be an increase in that
type of sleep in the next sleep period.

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Naps

A short period of sleep taken at any time of the day can help
with sleep credit/debit but it depends on the individual and the
sleep stages he passes through. After awakening from a nap
the responses and reactions will be slower for approximately 5
minutes. Habitual nappers seem to gain more benefit than non-
habitual nappers, when it lasts for at least 10 minutes or more.

Aids to Sleep

If you need to sleep whilst still in sleep credit ie you are going to
start a new shift at midnight after being ‘off’ for the past two
days, then:

 Make sure the bed is comfortable.
 No daylight, air-conditioning working in the room.
 Avoid too much coffee (caffeine) before bed time.
 Avoid mental stimulation, emotional stress and any
physical exercise before retiring.
 Warm milky drinks, light reading help promote relaxation.
 Alcohol – if used in moderation induces sleep but the
REM sleep will be reduced and early waking is likely.
 Drugs to aid sleep are sometimes used to break
insomnia. Drugs such as valium and mogadon, which
are also used to break stress conditions, also promote
sleep.

5.1 SLEEP DISORDERS

Narcolepsy: An inability to stop falling asleep even when in
sleep credit. This condition is clearly undesirable as the sufferer
may go into sleep even in a dangerous situation.

Apnoea: A cessation of breathing whilst asleep. This is quite a
common condition and the subject will normally either wake up
or restart breathing after a short time. It becomes a more
serious problem when the breathing stoppage lasts for up to a
minute and the frequency of stoppages increases. The frequent
wakening will disturb the normal sleep pattern and the individual
may experience excessive daytime sleepiness. Other clinical
problems may be involved and medical advice should be
sought.

Sleepwalking (Somnambulism): This condition, as well as
talking in one have sleep, is commoner in childhood, but does
occur later in life. It may occur more frequently in those
operating irregular hours or those under some stress. The
condition should not cause difficulty in healthy adults unless the
sleep walker is involved in an accident whilst away from his bed.

INSOMNIA: This is simply the term for difficulty in sleeping. It
may be divided into:
 CLINICAL INSOMNIA – where the individual is unable
to sleep at a time when they should be asleep. The
condition is often overestimated by the sufferer as there is
no absolute required quantity of sleep.
 SITUATIONAL INSOMNIA - where there is an inability
to sleep due to disrupted work/rest patterns or circadian
disrhythmia.

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Fatigue: This, in the medical sense, is not easy to measure. It
is associated with a heavy physical and/or mental workload
together with sleep deprivation and a lack of rest periods.

Fatigue is increased by working during sleep periods, working
longer hours, rotating shift patterns, complexity of the task and
environmental factors such as excessive heat and humidity.

When a person is feeling fatigued he is more likely to make a
number of errors, that can result in an aircraft accident or
incident.

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SECTION 6: ALCOHOLISM, MEDICA TION AND DRUG
ABUSE

Alcohol is a simple molecule, when taken orally requires no
digestion and is absorbed readily by the stomach and the initial
part of the small intestine. The rate of absorption depends on
the concentration in the stomach and duodenum. Water speeds
up absorption whilst foods high in protein slow the rate of
absorption. Once in the blood it passes immediately through
the liver.

The levels of alcohol have a marked effect on the naive drinker,
but ‘tolerance’ to alcohol is altered by large amounts of
consumption altering the central nervous systems sensitivity
over time.

Alcohol is a sedative – hypnotic drug, and can have a damaging
effect on the human body. Excessive consumption of alcohol
over a period of time can lead to cirrhosis of the liver. It can
also prevent the liver from metabolising the vitamin thiamine.
Thiamine deficiency leads to the loss of brain neurons, and
leads eventually to amnesia. When a person becomes
dependant on this drug we say he is an alcoholic. The
removal/withdrawal of alcohol from this individual results in
psychomotor agitation. The earliest and most common signs of
withdrawal are:
 Anxiety
 Anorexia
 Insomnia
 Tremors

The alcoholic may at times appear hyper alert, irritable, easily
startled and manifest jerky movements. Withdrawal may also
lead to disorientation and hallucinations which can induce fear
in some people.

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Tolerance

A male weighing 150 lb (68.2kg) metabolises alcohol at the rate
of approximately one drink per hour. A drink being 25 millilitres
of pure alcohol provided by the following:

 One measure of spirits (30 ml of 40-50% alcohol by
volume)

 A glass of wine (150 ml of 12% alcohol by volume)

 A pint of beer (400 ml of 5% alcohol by volume)

The Relationship Between Blood Alcohol Levels and
Behaviour In A Naïve Drinker

Blood
Levels (%)
BEHAVIOUR
0.05 Perceptible changes in mood and behaviour.
Judgement and restraint are loosened. The
individual feels carefree.
0.10 Voluntary motor action becomes clumsy. Legal
evidence of intoxication in most states.
0.20 The function of the entire motor area of the
brain is measurably depressed, causing
staggering. The individual may be easily
angered, and may shout or weep.
0.30 Confusion; stupor
0.40 Coma
0.50 Death due to respiratory blocking effects on the
medulla.

If a person was found to have 0.5% of blood alcohol and in a
stupor, we would deduce a high tolerance to alcohol and a
possible alcoholic.

Early significant landmarks of ensuing alcoholism are:

 Constant drinking for relief of tension and anxiety
(possibly brought on by stress)
 Psychological dependence
 Onset of memory blackouts
 Surreptitious drinking
 Urgent need to drink
 Increased tolerance to increasing amounts of alcohol

Chronic Stage

 Inability to stop drinking
 Loss of outside interest
 Work and money troubles
 Neglect of food
 Personal relationship difficulties
 Feelings of guild, remorse and depression
 Loneliness

When recognition of the above symptoms by ones self, a friend
or supervisor the alcohol excess requires prompt treatment.

Help and support to treat this abuse/addiction must come from
your local health centre, support groups like Alcoholics
Anonymous and finally, hopefully, your friends and family.
Continued drinking results in damage to the liver, cirrhosis and
alcoholic hepatitis. The body will suffer from muscle, skeletal,
pancreas, heart and brain disorders.

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Drugs

Drugs may be taken for medical reasons and may be prescribed
by a doctor or purchased from a pharmacy. If they have
adverse side effects then appropriate warnings will be given on
the label/literature which comes with the drugs.

Read the instructions carefully and take note of any warnings. If
drowsiness or inability to concentrate occurs do not drive or
work on aircraft – or carry out certification. It is possible that
you can transfer to another job during the period of medication.
If side effects are severe, see your doctor.

Remember to ‘trial’ any new prescribed medicines several days
prior to going to work to check for side effects.

Drugs today are taken by some people for recreational
purposes, which were not prescribed or bought over the counter
for their prescribed use. The drugs can vary from solvents,
cannabis, heroin, cocaine and ecstasy – there are many more.
The drug, how it is administered and the person will affect and
influence the development of drug abuse, leading to addiction.
Certain personality features have been identified that seem to
be characteristic of addicts:
 Emotional immaturity
 A strong wish to turn one’s back on reality
 A low frustration tolerance
 Unwillingness or inability to endure or cope with tension
 A lack of staying power

Withdrawal from the drug will cause sweating, tremors,
cravings, chills alternating with sweating. Continual abuse will
cause long term damage to the body and its organs.

Some employers are now testing employees for drugs. The
testing being carried out prior to employment for a safety
sensitive job and when someone contributes to a serious
accident at work. In some companies random drug testing is
carried out.

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LICENSED AIRCRAFT MA INTENANCE ENGINEERS
PERSONAL RESPONSIBIL ITY WHEN MEDICALLY U NFIT
OR UNDER THE INFLUENCE OF DRINK AND/OR DRUG S.
(Airworthiness Notices No 47)

The International Civil Aviation Organisation (ICAO) has
introduced an amendment to Annex 1 to the convention on
international civil aviation, which extends certain standards and
recommended practices to all licence holders. The changes
resulting from concerns of medical fitness and the use of
alcohol and drugs.

In the UK the ANO (Air Navigation Order) and AWN (Air
Worthiness Notice) 47 specify your responsibilities in this area.
The ANO article prohibits work on aircraft if the engineer
suspects that his/her condition (physical, mental or related to
drink or drugs) makes him/her unfit to perform his/her duties
correctly.

JAR66 also states that a person should not work on aircraft ie
exercise the privileges of their licence/authorisation, if their
mental condition renders them unfit to perform their tasks. It is
the responsibility of the individual NOT to work or carry out any
form of certification if he or she feels unfit in any way.
Management of approved organisations are to be aware of the
effects of the environment on the work staff and that their
employees are aware of their personal responsibilities. It is now
a legal requirement to monitor your own fitness for work.

FITNESS

If you are suffering from an illness etc, you will probably have
sought professional medical attention and have been certified
unfit for work. Conditions of your medical problem may be
obvious such as a head cold and you can self certify yourself
unfit for work under the current legislation.

Some unfit conditions may come-on gradually and may not be
apparent to the individual. Stress related conditions fall into this
category. It is possible under these circumstances for others to
notice the changes in an individual’s behaviour before the
person himself/herself recognises it. His/her family and friends
might notice, and more importantly, so might his/her work
colleagues.

Any gradual changes in a person’s behavioural pattern (dress,
habits etc) should be noted and the person concerned talked to
about the changes. Management should be informed so that
appropriate support and counselling actions can be taken.

Some examples of FIT FOR WORK are shown

STRESS – Some stress is essential for good performance, but
it becomes excessive then adverse mental and physical effects
can occur.

EYESIGHT – The engineer has to have a reasonable standard
of vision with the use of glasses or contact lenses if necessary.
He must be able to carry out tasks requiring near and far vision.
Colour perception should be tested and individual aware when
colour perception is required in his tasks.

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Companies should have procedures in place to address
problems of eyesight requirements. Signs in aircraft
manoeuvring areas or where colour coding used in aircraft
wiring.

DRUG AND ALCOHOL ABU SE – Is not acceptable where
aircraft safety is concerned and once identified will lead to
suspension of the licence or authorisation.

ALCOHOL – Has a similar effect to tranquillisers and can still
be circulating in the blood up to 8 hours after consumption. So
when ‘partying’ take note of when you are next on duty (or likely
to be called out for duty) and moderate you’re drinking
accordingly. Combining drink with drugs, sleeping tablets,
and/or anti-histamines etc can form a lethal cocktail.

ANAESTHETICS – After an anaesthetic – general, local or
dental, a period of up to 48 hours must elapse before going on
duty. The actual time will vary depending on the person and the
amount and type of anaesthetic administered.










MEDICINES IN COMMON USE

The following are some types of medicines which may impair
work performance. The list is not exhaustive. If the effects are
unknown for any prescribed drug seek expert medical advice
before their use.

Sleeping Tablets These dull the senses, cause mental
confusion and slow reaction times. The
duration of effect is variable from person
to person and may be unduly prolonged.
Individuals should have expert medical
advice before using them.

Tranquillisers Anti-depressants and sedatives depress
the alerting system and have been a
contributory cause of mistakes leading to
fatal accidents. Therefore a person
should not work when taking them.

Antibiotics Antibiotics (penicillin and the various
mycins and cyclines) and sulpha drugs
may have short term of delayed effects
which affect work performance. Their
use indicates that a fairly severe infection
may well be present and apart from the
effects of these substances themselves,
the side-effects of the infection will
almost always render an individual unfit
for work.

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Anti-Histamine Used widely in cold cures and in the
treatment of hay fever, asthma and
allergic skin conditions. Most of the
medicines tend to make the taker feel
drowsy. In general seek medical advice
and carry out a trial period before duty.

Pep Pills These may contain caffeine, benzedrine
and dexedrine. They are designed to
keep you awake and may be habit
forming. They can create a dangerous
feeling of over confidence. Over dosage
causes headaches, dizziness and metal
disturbances. Taking these pills whilst
working is NOT permitted. If coffee is
insufficient you are not fit for work.

High Blood
Pressure
(Hypertension)

Check with your doctor if any side effects
and if necessary carry out a pre work
trial.

Anti Malaria Pills As above.

Oral
Contraception
Pills
As above.

Sudafed

This is the trade name for a drug
prescribed by doctors for the relief of
nasal congestion. It may cause anxiety,
headache and effect performance. It is
NOT to be used whilst making
engineering decisions or performing
licensed duties.

Herbal Remedies Ask Chemist for possible side effects.
Carry out a pre work trial. If in doubt
check with your doctor.

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Human Factors
Chapter 5
PHYSICAL ENVIRONMENT

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Contents

SECTION 1: NOISE AND FUMES --------------------------------------------- 1
1.1 NOISE ------------------------------------------------------------------------- 1
1.2 FUMES ------------------------------------------------------------------------ 2
SECTION 2: ILLUMINATION -------------------------------------------------- 3
SECTION 3: ClIMATE AND TEMPERATURE ------------------------------- 5
3.1 VENTILATION ---------------------------------------------------------------- 7
SECTION 4: MOTION AND VIBRATION ------------------------------------ 8
4.1 VIBRATION ------------------------------------------------------------------- 8
SECTION 5: THE WORKING ENVIRONMENT ----------------------------- 9
5.1 WORKSPACE ----------------------------------------------------------------- 9
5.2 SUMMARY ------------------------------------------------------------------ 10

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SECTION 1: NOISE AND FUMES

1.1 NOISE

The impact of noise on human performance has already been
discussed earlier, Section 3 when examining ‘hearing’. To
recap, noise in the workplace can have both short-term and
long-term negative effects: it can be annoying, can interfere with
verbal communication and mask warnings, and it can damage
workers’ hearing (either temporarily or permanently). It was
noted that the ear is sensitive to sounds between certain
frequencies (20 HZ to 20 KHz) and that intensity of sound is
measured in decibels (dB), where exposure in excess of 115 dB
without ear protection even for a short duration is not
recommended. This equates to standing within a few hundred
meters of a moving jet aircraft.

General background noise can be ‘filtered out’ by the brain
through focused attention (as noted in Chapter 2, Section 3).
Otherwise, for more problematic noise, some form of hearing
protection (e.g. ear plugs and ear muffs) is commonly used by
aircraft maintenance engineers, both on the line and in the
hangar, to help the engineer to concentrate.

The noise environment in which the aircraft maintenance
engineer works can vary considerably. For instance, the airport
ramp or apron area is clearly noisy, due to running aircraft
engines or auxiliary power units (APUs), moving vehicles and
so on. It is not unusual for this to exceed 85 dB - 90 dB which
can cause hearing damage if the time of exposure is prolonged.

The hangar area can also be noisy, usually due to the use of
various tools during aircraft maintenance. Short periods of
intense noise are not uncommon here and can cause temporary

hearing loss. Engineers may move to and from these noisy
areas into the relative quiet of rest rooms, aircraft cabins, stores
and offices.

NOISE CAN BE THOUGHT OF AS ANY UNWANTED SOUND,
ESPECIALLY IF IT IS LOUD, UNPLEASANT AND ANNOYING.

It is very important that aircraft maintenance engineers remain
aware of the extent of the noise around them. It is likely that
some form of hearing protection should be carried with them at
all times and, as a rule of thumb, used when remaining in an
area where normal speech cannot be heard clearly at 2 meters.

In their day-to-day work, aircraft maintenance engineers will
often need to discuss matters relating to a task with colleagues
and also, at the end of a shift, handover to an incoming
engineer. Clearly, in both cases it is important that noise does
not impair their ability to communicate, as this could obviously
have a bearing on the successful completion of the task (i.e.
safety). Common sense dictates that important matters are
discussed away from noisy areas.

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1.2 FUMES

By its nature, the maintenance of aircraft involves working with
a variety of fluids and chemical substances. For instance,
engineers may come across various lubricants (oils and
greases), hydraulic fluids, paints, cleaning compounds and
solder. They will also be exposed to aircraft fuel and exhaust. In
fact, there is every possibility that an engineer could be exposed
to a number of these at any one time in the workplace.

Each substance gives off some form of vapour or fumes which
can be inhaled by the aircraft maintenance engineer. Some
fumes will be obvious as a result of their odour, whereas others
have no smell to indicate their presence. Some substances will
be benign most of the time, but May, in certain circumstances,
produce fumes (e.g. Overheated grease or oils, smouldering
insulation).

Fumes can cause problems for engineers mainly as a result of
inhalation, but they can also cause other problems, such as eye
irritation. The problem may be exacerbated in aircraft
maintenance engineering by the confined spaces in which work
must sometimes be carried out (e.g. fuel tanks). Here the fumes
cannot dissipate easily and it may be appropriate to use
breathing apparatus.

It may not always be practical to eradicate fumes from the
aircraft maintenance engineer’s work place, but where possible,
steps should be taken to minimise them. It is also common
sense that if noxious fumes are detected, an engineer should
immediately inform his colleagues and supervisor so that the
area can be evacuated and suitable steps taken to investigate
the source and remove them.


Apart from noxious fumes that have serious health implications
and must be avoided, working in the presence of fumes can
affect an engineer’s performance, as he may rush a job in order
to escape them. If the fumes are likely to have this effect, the
engineer should increase the ventilation locally or use breathing
apparatus to dissipate the fumes.

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SECTION 2: ILLUMINATION

In order that aircraft maintenance engineers are able to carry
out their work safely and efficiently, it is imperative that their
work be conducted under proper lighting conditions. It was
noted in earlier that the cones in the retina of the eye require
good light to resolve fine detail. Furthermore, colour vision
requires adequate light to stimulate the cones. Inappropriate or
insufficient lighting can lead to mistakes in work tasks or can
increase the time required to do the work.

When working outside during daylight, the engineer may have
sufficient natural light to see well by. It is possible however that
he may be in shadow (possibly caused by the aircraft) or a
building. Similarly, cramped equipment compartments will not
be illuminated by ambient hangar lighting. In these cases,
additional local artificial lighting is usually required (known as
task lighting).

At night, aerodromes may appear to be awash with floodlights
and other aerodrome lighting, but these are unlikely to provide
sufficient illumination for an engineer to be able to see what he
is doing when working on an aircraft. These lights are not
designed and placed for this purpose. Again, additional local
artificial lighting is needed, which may be nothing more than a
good torch (i.e. one which does not have a dark area in the
centre of the beam). However, the drawback of a torch is that it
leaves the engineer with only one hand available with which to
work. A light mounted on a headband gets round this problem.

Within the hangar, general area lighting tends to be some
distance from the aircraft on which an engineer might work, as it

is usually attached to the very high ceiling of these buildings.
This makes these lights hard to reach, meaning that they tend
to get dusty, making them less effective and, in addition, failed
bulbs tend not to be replaced as soon as they go out. In
general, area lighting in hangars is unlikely to be as bright as
natural daylight and, as a consequence, local task lighting is
often needed, especially for work of a precise nature
(particularly visual inspection tasks). Illumination refers to the
lighting both within the general working environment and also in
the locality of the engineer and the task he is carrying out. It can
be defined as the amount of light striking a surface. A torch can
be very useful to the engineer, but Murphy’s Law dictates that
the torch batteries will run down when the engineer is across
the airfield from the stores. It is much wiser to carry a spare set
of batteries than ‘take a chance’ by attempting a job without
enough light.

It is also important that illumination is available where the
engineer needs it (i.e. both in the hangar and on the line). Any
supplemental task lighting must be adequate in terms of its
brightness for the task at hand, which is best judged by the
engineer. When using task lighting, it should be placed close to
the work being done, but should not be in the engineer’s line of
sight as this will result in direct glare. It must also be arranged
so that it does not reflect off surfaces near where the engineer
is working causing indirect or reflected glare. Glare of either
kind will be a distraction from the task and may cause mistakes.
Poor ambient illumination of work areas has been identified as a
significant deficiency during the investigation of certain
engineering incidents. It is equally important that lighting in
ancillary areas, such as offices and stores, is good.

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Relying on touch when lighting is poor is no substitute for
actually being able to see what you are doing. If necessary,
tools such as mirrors and borescopes may be needed to help
the engineer see into remote areas. An extract from the NTSB
report on the Northwest Airlines accident at Tokyo, 1994,
illustrates these points:

“The Safety Board believes that the "OK to Close" inspector was
hindered considerably by the environment of the pylon area. He
indicated, for example, that the combination of location of the
scaffolding (at a level just below the underside of the wing that
forced him into unusual and uncomfortable physical positions)
and inadequate lighting from the base of the scaffolding up
toward the pylon hampered his inspection efforts. Moreover, the
underside of the pylon was illuminated by portable fluorescent
lights that had been placed along the floor of the scaffolding.
These lights had previously been used in areas where airplanes
were painted, and, as a result, had been covered with the
residue of numerous paint applications that diminished their
brightness. These factors combined to cause the inspector to
view the fuse pin retainers by holding onto the airplane structure
with one hand, leaning under the bat wing doors at an angle of
at least 30°, holding a flashlight with the other hand pointing to
the area, and moving his head awkwardly to face up into the
pylon area.”

The AAIB report for the BAC 1-11 accident says of the
unmanned stores area:

“The ambient illumination in this area was poor and the Shift
Maintenance Manager had to interpose himself between the
carousel and the light source to gain access to the relevant
carousel drawers.


He did not use the drawer labels, even though he now knew the
part number of the removed bolt, but identified what he thought
were identical bolts by placing the bolts together and comparing
them.” He also failed to make use of his spectacles.

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SECTION 3: CLIMATE AND TEMPERATURE

Humans can work within quite a wide range of temperatures
and climatic conditions, but performance is adversely affected at
extremes of these. Thus, as can be seen in Figure 5.1, when it
is too cold and/or wet or too hot and/or humid, performance
diminishes.

As has been noted throughout this document, aircraft
maintenance engineers routinely work both within the hangar
and outside. Clearly, exposure to the widest range of
temperature and climate is likely to be encountered outdoors.
Here, an engineer may have to work in direct summer sun,
strong winds, heavy rain, high humidity, or in the depths of
winter. Although hangars must exclude inclement weather, they
can be cold and draughty, especially if the hangar doors have to
remain open.

EASA part 145.A.25 (c) 1 states that

“Temperatures must be maintained such that personnel can
carry out required tasks without undue discomfort.”

Unfortunately, in reality, pressure to turn aircraft round rapidly
means that some maintenance tasks are not put off until the
conditions are more conducive to work. Environmental
conditions can affect physical performance.

For example, cold conditions make numb fingers, reducing the
engineer’s ability to carry out fiddly repairs, and working in
strong winds can be distracting, especially if having to work at
height (e.g. on staging). Extreme environmental conditions may
also be fatiguing, both physically and mentally.


There are no simple solutions to the effects of temperature and
climate on the engineer. For example, an aircraft being turned
around on the apron cannot usually be moved into the hangar
so that the engineer avoids the worst of the weather. In the cold,
gloves can be worn, but obviously the gloves themselves may
interfere with fine motor skills. In the direct heat of the sun or
driving rain, it is usually impossible to set up a temporary shelter
when working outside.

There was an instance in Scotland, where work on an aircraft
was only suspended when it became so cold that the lubricants
being used actually froze.

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Fig 5.1 The relationship between climate, temperature and
performance

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3.1 VENTILATION

Most hangars and workshops have good ventilation, (hangars
are draughty places anyway) and air quality is not such a
problem.

If we are working in an enclosed workplace, it should be
ventilated with fresh air at a rate of, at least, 5 to 8 litres per
second, per occupant. The air should be free of impurities, by
not siting the inlet near heating exhausts or near vehicle
manoeuvre areas. Where necessary the inlet air should be
filtered to remove particles. If air conditioning is used the
system should be regularly cleaned, tested and maintained to
ensure that they are kept clean and free from anything which
may contaminate the air.

Natural ventilation, by opening windows, should not result in
uncomfortable draughts.

Mechanically forced ventilation can also cause draughts and
screening may have to be used or work stations re-sited.

When carrying out any of the following operations, special
precautions must be taken:

 Paint removal – chemical or blasting
 Paint spraying – or other application methods if fumes
are excessive
 Grit blasting
 Sweeping hangar floors
 Removing cabin insulation, carpets etc.
 Chemical process, such as chemical de-greasing etc.

PERSONAL BREATHING MASKS/HOODS SHOULD BE
WORN TO ENSURE A CLEAN AIR SUPPLY AND PREVENT
DAMAGE TO THE LUNGS!

Care must be taken when working in enclosed spaces with
ground equipment powered by internal combustion engines for
the possible build up of DANGEROUS CARBON MONOXIDE
gases. Carbon monoxide (Co) is a poisonous gas and is a
product of incomplete combustion of fuel. It is found in varying
degrees in all smoke and fumes from burning carbonaceous
substances. It is colourless, odourless and tasteless.

Symptoms of poisoning by carbon monoxide are:-

 Nausea

 Headaches

 Vomiting leading to unconsciousness

 Death, depending on the concentration and time
exposed

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SECTION 4: MOTION AND VIBRATION

Aircraft maintenance engineers often make use of staging and
mobile access platforms to reach various parts of an aircraft. As
these get higher, they tend to become less stable. For example
when working at height on a scissors platform or ‘cherry picker’,
applying force to a bolt being fixed to the aircraft may cause the
platform to move away from the aircraft. The extent to which this
occurs does not just depend on the height of the platform, but
its design and serviceability. Any sensation of unsteadiness
may distract an engineer, as he may concentrate more on
keeping his balance than the task. Furthermore, it is vitally
important that engineers use mobile access platforms properly
in order to avoid serious injury.

Vibration in aircraft maintenance engineering is usually
associated with the use of rotating or percussive tools and
ancillary equipment, such as generators. Low frequency noise,
such as that associated with aircraft engines, can also cause
vibration. Vibration between 0.5 Hz to 20 Hz is most
problematic, as the human body absorbs most of the vibratory
energy in this range. The range between 50-150 Hz is most
troublesome for the hand and is associated with Vibratory-
induced White Finger Syndrome (VWF). Pneumatic tools can
produce troublesome vibrations in this range and frequent use
can lead to reduced local blood flow and pain associated with
VWF. Vibration can be annoying, possibly disrupting an
engineer’s concentration.

4.1 VIBRATION

Many engineers will never suffer this as a problem because
they do not work for long periods with equipment/machinery that
vibrates to any great extent. Hand Arm Vibration Syndrome
(HAVS) is the name given to a group of diseases of which the
most widely known is VIBRATION WHITE FINGER . Workers
using hand held tools and equipment, such as pneumatic
riveting guns, are at risk of exposure. Vibration of the whole
body, through the seat or platform of a machine is associated
with lower back pain.

A recent Health and Safety Executive (HSE) report found 4.9
million people are usually exposed to hand transmitted vibration
in a one week period, of which 1.2 million were exposed to
vibration levels above that which the HSE recommends.
242,000 cases of Vibration White Finger are likely to be
attributable to hand arm vibration.

Methods of reducing vibration induced problems include:

 Reducing the exposure time of the operator.
 Manufacturing equipment so that frequencies are
outside the critical range.
 Reducing the amplitude of the vibration by increasing
the weight of the tool or reducing the force of the forcing
function.
 Providing damping material between the object/tool and
the operative

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SECTION 5: THE WORKING ENVIRONM ENT

5.1 WORKSPACE

Workrooms should have enough free space to allow people to
get to and from work stations and to move within the room with
ease. The number of people who may work in any particular
room at any time will depend not only on the room size but on
the space taken up by furniture, fittings, equipment and the
room layout. The minimum workspace is 11 cubic metres per
person and may be insufficient if furniture etc. is included.

The Working Environment

Ergonomics is the study of the relationship between workers
and their environment. Ergonomics is about ensuring a good
‘fit’ between people and the machines/equipment they use.
Ergonomics should mean ‘fitting the task to the man’ rather than
‘fitting the man to the task’.

Within this topic is work study and work measurement. Whilst
this is being carried out, poorly designed work equipment and
unsafe practices can be dealt with at the same time.

The skills of an ergonomist include:

 Anthropometry
 Physiology
 Psychology
 Engineering

Anthropometry

This is a study of human measurements such as shape, size
and range of joint movements. The machine will be designed to
suit a wide range of sizes of man, using statistical analysis.

Physiology

This is a study of the calorific requirements of work, body
functions, the reception of stimuli processing and response.
The Man and Machine must be complementary

Psychology

As previously discussed in these notes, but will include
DISTRACTION and FATIGUE.

Engineering

This is involved in the design of tools and machines where the
user is able to apply the necessary force, are natural to operate
etc. Standardisation should also be a concern of the engineer.

For Example:

A good example can be seen on the flight decks of the Boeing
757 and 767. These are identical in layout making life so much
easier for engineers and pilots alike to transfer between the two
types.

Design can reduce operation errors.

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5.2 SUMMARY

So, when we set up a hangar aircraft maintenance facility or a
workshop, we have to consider the physical effects, the
ergonomics and the psychological effects on the people
employed. The effects of heat, noise etc. are, over a space of
time, going to cause fatigue in the individual, so reducing his
performance and, in the long term, affecting his physical health.
The ergonomics of the workplace, i.e. the efficient layout of the
aircraft, equipment and facilities in the hangar, will also affect
the engineer’s performance by reducing fatigue. Distraction in
the workplace by noise, movement of personnel within the
immediate work area, and telephones ringing can be alleviated
by careful screening, soundproofing and regulated access to
work areas. This will minimise maintenance errors due to
unwarranted distractions.

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Human Factors
Chapter 6
TASKS

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Contents

SECTION 1: PHYSICAL WORK ------------------------------------------------ 1
1.1 INTRODUCTION ------------------------------------------------------------- 1
1.2 Body Movements ---------------------------------------------------------- 2
1.3 PLANNING ------------------------------------------------------------------- 4
SECTION 2: REPETITIVE TASKS ---------------------------------------------- 6
SECTION 3: VISUAL INSPECTION -------------------------------------------- 8
SECTION 4: COMPLEX SYSTEMS -------------------------------------------- 9

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SECTION 1: PHYSICAL WORK

1.1 INTRODUCTION

Many of the tasks of the aircraft engineer requires physical
effort ranging from visual inspections to more complex tasks
such as engine installation and testing. The task in hand may
require standing, sitting or some other position of the body. It
will require the use of the senses with correct body movements
as commanded by the brain.

Clothing

Before commencing work the engineer should be correctly
dressed for the task in hand. Overalls should be of a good fit
and comfortable whilst working in odd body positions. The
overalls should only have pockets that can be secured. Pockets
should be empty except for essential work items. It is good
practice not to have loose personal items on one’s person whilst
working on aircraft which might form a FOD hazard. After
working on an aircraft a check should be made to ensure that all
items in the pockets are accounted for.

The amount and type of clothing will depend on the temperature
and the nature of the task. As more clothing is worn, the
movement of the torso, arms and legs is restricted.
Boots/shoes should be non-slip, not affected by fuels/oils, non-
spark making and will not cause aircraft structures to be
scratched. Ideally the footwear will incorporate a safety toe cap.

Body Posture

The height of the vice/bench should be related to the ‘elbow
height’ of the person using the bench. For filing/machinery work

the work piece should be 5cm lower than elbow height. When
carrying out visual inspections the work piece should be
between elbow height and 25cm above. The floor should be
firm and level, but if standing for long periods, duckboarding is
advantageous. Remember that the duckboard is there when
moving to and from the workstation.

If you are required to work on the outside of an aircraft, standing
can be hazardous due to the shape and slippery surface due to
oil, water, ice etc. Be aware of designated walk zones. If also
working at height, consider wearing safety harness and placing
site warning notices below. This is in case tools and equipment
fall and injure someone below. Avoid overstretching whilst
working and ensure guard rails are in position on platforms.

Sitting at a workstation should be comfortable and capable of
adjustment. Unsuitable workbench height causes the operator
to develop musculoskeletal problems. If the workbench is too
high then the operator has to adopt an unnatural posture, with
the elbows away from the body and the shoulders rose. This
causes discomfort in the shoulders and neck. If the work
surface is too low then the operator will have to lean forwards.
This causes neck and lower back problems. Repetitive motions,
particularly those requiring the operator to exert force or use
some unnatural motion, can lead to repetitive strain injury.

When lying on your back under an aircraft use a crawler board if
possible and if lying on your side use a cushion for the head to
reduce straining the neck muscles.

Kneeling - Use kneepads or other suitable padded material. Try
to be supported by the full length of the lower leg whilst
kneeling.

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1.2 BODY MOVEMENTS

Lifting and Carrying – Always try to avoid strain. If something
is too heavy to lift without strain then get a friend to help you or
use lifting equipment. If the item is too bulky then again, get
assistance, or use lifting equipment.

When lifting an item from floor level, always bend the knees,
with the legs slightly apart. Lift the item using the muscles in the
legs, trying to keep the back reasonably straight. If the item
cannot be lifted this way, then get some assistance. The back
muscles are very powerful, and if the back is bent to lift a heavy
object, their power can put considerable strain on the spinal
column and cause injury.

When straightening up, keep the arms bent and the item as
close to the body as possible. Holding the item away from the
body produces a moment which the back muscles have to
counteract – placing additional strain on the spinal column.

When carrying anything heavy keep it close to the body and
restrict the amount of time it is being held. A battery, for
example, is a reasonably easy item to lift – even though it is
heavy. But if the lift continues for a period of time, say when
carrying, then strain can be caused to the back and back pain
can result. This may not be immediately apparent, but may
show up some time later – when in bed that night for example.








Twisting – Whilst carrying a load or when applying a force, say,
when drilling and hammering, twisting should be avoided as it
can also lead to back problems.

Pulling – NEVER pull anything (aircraft etc.) which could run
you over (roll-over) once it gets moving. NEVER strain when
pulling. The same applies to pushing.

If a wheeled vehicle is being moved ensure that it has a
serviceable brake system or some other means of stopping its
movement. If it won’t move with a reasonable push/pull, get
some help from a colleague or mechanical means. Whatever
you do, DO NOT STRAIN.

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If the item you are pushing/pulling moved unexpectedly, make
sure you are in no danger from roll-over or from overbalance.

Reaching – Ideally, whatever you are working on should be no
more than a forearm’s length away from the body torso.
NEVER over-reach yourself on any job, particularly at height, as
this may cause overbalance with possible serious
consequences.

Hands – In previous chapters, we talked about repetitive strain
injury such as, vibration white finger. It is therefore important to
hold tools correctly to avoid injury.

For Example:

 When drilling, riveting or using any tools, the best
position for the wrist/hand is the fingers closed
around a handle of 1 to 1½ in. in diameter (25 to 38
mm) with the thumb going in the opposite direction.
The handle to be in at right angles to the forearm.

Working at Height – On certain aircraft types, often due to their
physical size, we require equipment such as:

 Ladders
 Adjustable work platforms
 Aircraft docking systems
 Safety harnesses

The design of the equipment is governed by local country
regulations. In the UK, the British Standards Institute (BSI)
makes sure the equipment you use is safe for its designated
use, and conforms to regulations.


Most firms will have in place a maintenance programme for the
equipment with a recording and identification system to ensure
that it is serviceable and it has suitable documentation to
confirm its service history (an attached wallet containing a
signed servicing recorder example).

When using height adjustable work platforms, the following
precautions should be observed:

 Steady feet in position before rising – if fitted.

 Never overload the platform. Safe working load (SWL)
will be indicated on the side of the platform.

 Never overbalance the platform – load evenly,
distributed on top.

 Always ensure guardrails are in position.

 When raising/lowering, ensure personnel and aircraft
structures are clear.

 Protect structure from platform damage using fender
cushions (rubber protective fenders).

 Keep gap between structure and platform as narrow as
possible.

 Use safety locks when raised into position.

Docking systems have similar problems to those of working
platforms. They are far more extensive with several stories with
steps to each, purpose-built for the specific type of aircraft being
maintained.

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Guardrails around working platforms should be approximately
waist height with a low level screen to prevent small objects,
sockets etc. from falling off.

Working at height outside the aircraft, on a ladder or platform at
3 metres or more from the ground, a safety harness should be
worn. It should be of an approved type and secured to the
platform. When working on a ladder, it should be secured to a
strong point on the aircraft.

If you suffer from acrophobia (fear of heights) you should only
work at a height at which you feel comfortable.

Working in enclosed spaces – sometimes engineers can be
asked to work in very small areas, such as aircraft fuel tanks. In
this case, company procedures will lay down specific rules and
safety precautions that must be followed.

If you suffer from claustrophobia (fear of enclosed spaces) you
should not be expected to undertake this kind of work.

1.3 PLANNING

Blindly starting a task without planning how best to do it is
almost certainly the best way to invite problems. Before
commencing a task, an individual engineer, engineering team or
planner should ask themselves a number of questions. These
may include:

 Do I/we know exactly what the task is that has to be
done?

 Are the resources available to do it effectively (safely,
accurately and within the time permitted)? Where
resources include:
 Personnel
 Equipment/spares
 Documentation, information and guidance
 Facilities such as hangar space, lighting, etc.
 Do I/we have the skills and proficiency necessary to
complete the task?

Information about specific tasks should be detailed on job cards
or task sheets. These will indicate the task (e.g. checks or
inspection, repair, replacement, overhaul) and often further
details to aid the engineer (such as maintenance manual
references, part numbers, etc.).

It is generally the shift supervisor’s job to ensure that the
resources are available for his staff to carry out their tasks. As
noted earlier (‘Time Pressure and Deadlines’), it is likely that,
within a shift or a team, various sub-tasks are allocated to
individuals by the supervisor.

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Alternatively, he may encourage a team to take ownership of
the tasks that need to be completed, giving them the discretion
to manage a package of work (as noted earlier (‘Team
Working’). Exactly ‘who does what’ is likely to be based on
factors such as individuals’ specialization (i.e. A&C or avionics)
and their experience with the task.

Although management have a responsibility to ensure that their
engineers have suitable training, at the end of the day, it is up to
the individual engineer to decide whether he has the necessary
skills and has the proficiency and experience to do what he has
been asked to do. He should not be afraid to voice any
misgivings, although it is recognized that peer and management
pressure may make this difficult. If the engineer is in any doubt
what needs to be done, written guidance material is the best
resource. Colleagues may unintentionally give incorrect or
imprecise direction (the exception to this is discussing problems
that arise that are not covered in the guidance material).

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SECTION 2: REPETITIVE TASKS

Tasks are normally classed as repetitive if the task duration is
comparatively short and task frequency is high. It is also related
to how often the task is performed.

If you were tasked to fit 5 rivets it could hardly be classed as a
repetitive task, but if you had to put the same rivets in day after
day for months on end, then that would constitute a repetitive
task.

Larger tasks on aircraft can also become repetitive.

For Example:

A turnaround inspection on one particular aircraft type carried
out several times a day and so on over several months.

If a task does become repetitive, then boredom will start to
creep in, our arousal level is low, there is reduced motivation
and the individual is likely to make mistakes. From the notes on
information processing and perception we saw that, after the
initial stages of using the perception area of the brain with the
central processor and using long and short term memories the
MOTOR MEMORY is likely to take over with an occasional
monitoring function from the central processor.

The person who is now carrying out a repetitive task can carry it
out without putting in much REAL THOUGHT. Whilst working,
the person can think of other things - the mind can ‘wander’ and
mistakes can happen.

In the interests of safety, once you realise that a task has
become repetitive, management should be informed and you
should be moved into another job. A job change is not always
possible so, in the meantime, there are four ways to prevent
boredom and the adoption of a complacent attitude:

 Take regular short breaks – a few minutes will help

 Try and break the work pattern with a different task if
possible

 Change positions

 Check manuals from time to time to confirm you are
following the correct procedure

Repetitive tasks can be reduced by moving people around from
time to time, within a team so each person has a variety of tasks
to do.

Repetitive tasks can be tedious and reduce arousal (i.e. be
boring). Most of the human factors research associated with
repetitive tasks have been carried out in manufacturing
environments where workers carry out the same action many
times a minute. This does not generally apply to maintenance
engineering. Some engineers may specialize in a certain aspect
of maintenance, such as engines. As a result, they may possibly
carry out the same or similar tasks several times a day.

The main danger with repetitive tasks is that engineers may
become so practiced at such tasks that they may cease to
consult the maintenance manual, or to use job cards.

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Thus, if something about a task is changed, the engineer may
not be aware of the change. Complacency is also a danger,
whereby an engineer may skip steps or fail to give due attention
to steps in a procedure, especially if it is to check something
which is rarely found to be wrong, damaged or out of tolerance.
This applies particularly to visual inspection, which is covered in
greater detail in the next section.

Making assumptions along the lines of ‘Oh I’ve done that job
dozens of times!’ can occur even if a task has not been
undertaken for some time. It is always advisable to be wary of
changes to procedures or parts, remembering that ‘familiarity
breeds contempt’.

Repetitive tasks in aircraft maintenance engineering typically
refer to tasks that are performed several times during a shift, or
a number of times during a short time period, e.g. in the course
of a week. An example of this would be the checking life jackets
on an aircraft during daily inspections. In the Aloha accident
report, the NTSB raised the problem of repetitive tasks:

“The concern was expressed about what kinds of characteristics
are appropriate to consider when selecting persons to perform
an obviously tedious, repetitive task such as a protracted NDI
inspection. Inspectors normally come up through the seniority
ranks. If they have the desire, knowledge and skills, they bid on
the position and are selected for the inspector job on that basis.
However, to ask a technically knowledgeable person to perform
an obviously tedious and exceedingly boring task, rather than to
have him supervise the quality of the task, may not be an
appropriate use of personnel…”

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SECTION 3: VISUAL INSPECTION

The process of inspection by using our eyes supported by visual
aids and backed up by test equipment is the main process by
which we ascertain the serviceability of an aircraft and its
equipment. We use our senses of feel, smell and hearing, but
vision is the sense we mostly rely on.

We have previously discussed how the eye/brain works and the
‘tricks’ of perception which will affect how we detect visual
defects in aircraft and components. Engineers should also be
aware of their eyesight limitations and the need for glasses or
contact lenses to correct focusing defects.

The physical environment, hopefully, is ideal for the person to
carry out the visual inspection, ie. adequate lighting, heating,
ventilation and low noise levels. Whilst the engineer is carrying
out his inspection, it is advisable to prevent/minimise any
distractions which will disturb his short term memory and
concentration. This can be by preventing ‘visitors’ talking to the
engineer directly at his workstation and any disrupting noises
such as telephone calls.

The lighting for visual inspections should be sufficient and of the
correct type. The wrong type of light source can cause
problems with colour perception. Engineers should inform
management of any colour perception (colour blindness)
problems so that the person should work only on tasks that are
not colour dependent for satisfactory completion. For example
colour identification of cables and flight deck instrument decals.
If in doubt about colour, assistance should be sought for
confirmation of its correct identification.

Whilst reading instruments and gauges always hold the scale so
it is parallel to a centre line running through the eyes of the
observer. This will help prevent PARALLAX ERROR . A light
held at the head height of the observer at 90 to the scale will
be an aid to help prevent parallax error. Some instruments have
mirrors behind the pointer so when the mirror image is in line
with the pointer there is no error.

When carrying out visual inspections, be aware of the effects
that can be caused by the blind spot in the eye. This can be
particularly important when examining a row of rivets for
example.

To minimise the effects of the blind spot, keep eye movements
short and frequent and try to avoid staring at one area for too
long.

Light and the physical limitations of the human eye can be
overcome by using visual aids, such as:

 Magnifying glasses
 Mirrors
 Boroscopes/Intrascopes
 Fibre optics
 Video cameras
 Colour television monitors

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SECTION 4: COMPLEX SYSTEMS

Modern aircraft, fixed and rotary wing have many systems
which combine mechanical and electronic features. Therefore to
maintain these systems/components more than one
trade/licence category is required.

On large pressurised aircraft, data from various systems is
recorded for the Flight Data recorder, but also is linked to
computers. A good example is the Air Data Computer.

This Digital Air Data Computer (DADC) takes pitot and static
pressures and converts them into a digital signal for the flight
data recorder and other computers to use. This air data can
then be used by the Full Authority Engine Control computer
(FADEC) to control engine performance and the Cabin
Pressurisation computer to control cabin altitude pressure.

From these examples we can see we need mechanical and
avionics engineers (under PART 66) and Electrical, Instrument,
Aeroplanes Engines (licensed engineer under BCAR Section L).

It is important that all engineers know the exact extent of their
responsibilities applicable to their licence/approval. Engineers
should have some knowledge of all systems beyond their
immediate certification responsibilities so they will have a better
understanding of any consequences occurring to other systems
or that particular system. The Duties and Responsibilities of a
Licensed Engineer are laid down for the UK by the CAA
publication CAP 455 Airworthiness Notices numbers 3 and 12.
These amplify the certification responsibilities in relation to the
Air Navigation Order & the Joint Airworthiness Regulations 145.

Airworthiness Notice No 3 specifies areas of trade responsibility
together with exclusions and limitations where work is NOT
PERMITTED by certain licence/authorisation holders. This
Notice also highlights the ‘overlap’ of responsibilities between
trade categories and the need for good ‘handovers’ at shift
changes. This Aircraft Legislation is expanded upon and
explained in detail in a separate Module and accompanying
notes.

The overlap of responsibilities occurs when two or more trades
are involved in a task, such as an engine change. The trade
mainly involved is the engine/mechanical category but
supported by the electrical/avionic engineer. Each trade takes
responsibility and signs a Certificate of Release to Service
(CRS) when he is happy that the task for which he is
licensed/approved to carry out, has been completed correctly.
The mechanical engineer’s duty is to oversee the task, ensure
that the avionic engineer has signed his CRS, before signing
himself to complete the work and release the aircraft to service.

When a task is long and/or complex the job card should be
written out in such a way as to break it down into stages. When
each stage is completed, and signed and dated, a continuous
record of the task’s status is maintained. This continuous record
is MOST IMPORTANT particularly to shift working and when
‘handing over’ an incomplete task to another engineer. Shift
handovers are a problem area where mistakes are made due to
communication failures. During handovers a DEBRIEFING
should occur between the ‘off-going’ engineer and the
‘on-coming’ engineer.

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The Debriefing should include:

 Checking the cards are signed and up-to-date
 A verbal explanation of the progress of the job to date
 An indication of any possible problems that may arise
 A situation report
 A progress report on the spares situation
 Expected completion date and time (operations –
programme)
 Possible exchange of telephone numbers for liaison
purposes

When all the separate trades’ work is completed and
serviceable it is important that nothing is left out, the aircraft as
a whole should be serviceable. The certifying engineer should
be aware of his Duties, Responsibilities and Limitations of his
licence category. He must ensure that all drawings and
manuals are up-to-date in their amendments, and that all
recordings of the work carried out is correctly documented.

Certain vital points, engine and flying controls are subject to
duplicate inspection and certification by appropriately licensed
engineers. This can be considered to be a Flight Safety Net
system to help prevent many errors due to human performance.

By good supervision, stage and duplicate inspections with the
appropriate tests on the ground and in the air, a safe,
serviceable aircraft will be fit for service, with a reduction in
failure due to human error.

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Human Factors
Chapter 7
COMMUNICATION

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Contents

SECTION 1: COMMUNICATION WITHIN & BETWEEN TEAMS ------ 1
1.1 COMMUNICATION --------------------------------------------------------- 1
1.2 WITHIN AND BETWEEN TEAMS ---------------------------------------- 1
1.3 MODES OF COMMUNICATION ----------------------------------------- 1
1.4 VERBAL AND WRITTEN COMMUNICATION -------------------------- 2
1.5 NON-VERBAL COMMUNICATION -------------------------------------- 2
1.6 COMMUNICATION WITHIN TEAMS ------------------------------------ 3
1.7 COMMUNICATION BETWEEN TEAMS --------------------------------- 3
1.8 COMMUNICATION PROBLEMS ----------------------------------------- 4
SECTION 2: WORKLOGGING & RECORDING ----------------------------- 7
SECTION 3: KEEPING UP TO DATE, CURRENCY UPDATING --------- 10
SECTION 4: DISSEMINATION OF INFORMATION ---------------------- 11

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SECTION 1: COMMUNICATION WITHIN & BETWEEN
TEAMS

1.1 COMMUNICATION

Good communication is important in every industry. In aircraft
maintenance engineering, it is vital. Communication, or more
often a breakdown in communication, is often cited as a
contributor to aviation incidents and accidents. This chapter
examines the various aspects of communication that affect the
aircraft maintenance engineer.

1.2 WITHIN AND BETWEEN T EAMS

As noted in previous chapters, aircraft maintenance engineers
often work as teams. Individuals within teams exchange
information and need to receive instructions, guidance, etc.
Moreover, one team will have to pass on tasks to another team
at shift handover. An engineer needs a good understanding of
the various processes of communication, as without this, it is
impossible to appreciate how communication can go wrong.

1.3 MODES OF COMMUNICATI ON

We are communicating almost constantly, whether consciously
or otherwise. An aircraft maintenance engineer might regularly
communicate:

 Information
 Ideas
 Feelings
 Attitudes and beliefs

As the sender of a message, he will typically expect some kind
of response from the person he is communicating with (the
recipient), which could range from a simple acknowledgement
that his message has been received (and hopefully
understood), to a considered and detailed reply. The response
constitutes feedback. Communication is defined in the Penguin
Dictionary of Psychology as:

“The transmission of something from one location to another.
The ‘thing’ that is transmitted may be a message, a signal, a
meaning, etc. In order to have communication both the
transmitter and the receiver must share a common code, so that
the meaning or information contained in the message may be
interpreted without error”.

As can be seen in the above definition, communication can be:

 Verbal/spoken - e.g. a single word, a phrase or
sentence, a grunt
 Written/textual - e.g. printed words and/or numbers on
paper or on a screen, hand written notes
 Non-verbal –
 Graphic - e.g. pictures, diagrams, hand drawn
sketches, indications on a cockpit instrument
 Symbolic - e.g. ‘thumbs up’, wave of the hand,
nod of the head
 Body language - e.g. facial expressions, touch
such as a pat on the back, posture

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1.4 VERBAL AND WRITTEN COMMUNICAT ION

Generally speaking, verbal and written communication is
purposeful. For a spoken or written message to be understood,
the sender has to make sure that the receiver:

 is using the same channel of communication

 recognizes and understands his language

 is able to make sense of the message’s meaning

The channel of communication is the medium used to convey
the message. For spoken communication, this might be face-to-
face, or via the telephone. Written messages might be notes,
memos, documents or e-mails. In the UK it is expected that
aircraft maintenance engineers will communicate in English.
However, it is also vital that the message coding used by the
sender is appreciated by the recipient so that he can decode the
message accurately. This means that engineers must have a
similar knowledge of technical language, jargon and acronyms.

Assuming the channel and language used are compatible, to
extract meaning, the engineer has to understand the content of
the message. This means that it has to be clear and
unambiguous. The message must also be appropriate to the
context of the workplace and preferably be compatible with the
receiver’s expectations. Where any ambiguity exists, the
engineer must seek clarification.

1.5 NON-VERBAL COMMUNICATION

Non-verbal communication can accompany verbal
communication, such as a smile during a face-to-face chat. It
can also occur independently, for instance a colleague may
pass on his ideas by using a sketch rather than the use of
words. It can also be used when verbal communication is
impossible, such as a nod of the head in a noisy environment.

Non-verbal communication is also the predominant manner by
which systems communicate their status. For instance, most
displays in the aircraft cockpit present their information
graphically.

Body language can be very subtle, but often quite powerful. For
example, the message “No” accompanied by a smile will be
interpreted quite differently from the same word said whilst the
sender scowls.

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1.6 COMMUNICATION WITHIN TEAMS

Individual aircraft maintenance engineers need to communicate:

 Before starting a task - to find out what to do

 During a task - to discuss work in progress, ask
colleagues questions, confirm actions or intentions, or
to ensure that others are informed of the maintenance
state at any particular time

 At the end of a task - to report its completion and
highlight any problems

Spoken communication makes up a large proportion of day-to-
day communication within teams in aircraft maintenance. It
relies both on clear transmission of the message (i.e. not
mumbled or obscured by background noise) and the ability of
the recipient of the message to hear it (i.e. active listening
followed by accurate interpretation of the message). Good
communication within a team helps to maintain group cohesion.

It is much less common for individuals within teams to use
written communication. They would however be expected to
obtain pertinent written information communicated by service
bulletins and work cards and to complete documentation
associated with a task.

1.7 COMMUNICATION BETWEE N TEAMS

Communication between teams is critica l in aircraft
maintenance engineering. It is the means by which one team
passes on tasks to another team. This usually occurs at shift
handover. The information conveyed will include:

 Tasks that have been completed

 Tasks in progress, their status, and any problems
encountered, etc.

 Tasks to be carried out

 General company and technical information

Communication between teams will involve passing on written
reports of tasks from one shift supervisor to another. Ideally, this
should be backed up by spoken details passed between
supervisors and, where appropriate, individual engineers. This
means that, wherever necessary, outgoing engineers personally
brief their incoming colleagues. The written reports
(maintenance cards, procedures, work orders, logs, etc.) and
warning flags / placards provide a record of work completed and
work yet to be completed - in other words, they provide
traceability. Furthermore, information communicated at shift
handover ensures good continuity. It is important that
handovers are not rushed, so as to minimize omissions.

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1.8 COMMUNICATION PROBLE MS

There are two main ways in which communication can cause
problems. These are lack of communication and poor
communication. The former is characterized by the engineer
who forgets to pass on pertinent information to a colleague, or
when a written message is mislaid. The latter is typified by the
engineer who does not make it clear what he needs to know
and consequently receives inappropriate information, or a
written report in barely legible handwriting. Both problems can
lead to subsequent human error. Spoken messages provide
considerable flexibility and informality to express work-related
matters when necessary. The key to such communication is to
use words effectively and obtain feedback to make sure your
message has been heard and understood.

Communication also goes wrong when one of the parties
involved makes some kind of assumption. The sender of a
message may assume that the receiver understands the terms
he has used. The receiver of a message may assume that the
message means one thing when in fact he has misinterpreted it.
Assumptions may be based on context and expectations, which
have already been mentioned. Problems with assumptions can
be minimized if messages are unambiguous and proper
feedback is given.

The most important distortions and misunderstandings occur in
vertical communications, especially where messages change
from oral to written and vice versa. Departments tend to operate
in isolation and in larger organisations this can lead to strained
and difficult communications. There are other barriers which
must be overcome if successful communication is to take place,
such as perceptions, jargon, technical words and process
difficulties.

Perception

If the transmitter of a message wrongly perceives the receiver
he will use the wrong language and medium for transmission of
that message. Similarly if the receiver has a perceived image of
the sender ie. he thinks he is a ‘bit of an old granny’ then the
message received might not be treated with the respect and
urgency the transmitter desired.

Jargon

With modern technology there are a large number of words,
phrases and acronyms being used in communication. When a
member of one group communicates with a member of another
group, problems can occur because of the different language
being used within each group.

Technical Words

The transmitter of the message must know his audience. If
technical words are used to communicate to a non-technical
person/group, the sense of the message will become difficult
and may be lost.

Process Difficulties

If there is a difficult message to be communicated and there is
no ‘feedback’ a problem may exist as a result of the message
not being correctly transmitted or understood.

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Verbal Reports

If a message is straightforward and simple, and the other
person is easily reached, then you might prefer to talk to him
personally. The message might be for his ears alone, or he
might need to be shown something. If the information is
relatively simple and easily understood a short ‘briefing’ may be
given to a group in order that it can be passed easily to their
subordinates and so on amongst the employees.

The disadvantage is that the message can change as it is
conveyed down the line. The classic example is the army
message sent back from the front line to headquarters:

‘Send reinforcements we’re going to advance.’

Unfortunately, by the time it reached headquarters, the
message had become:

‘Send three and fourpence we’re going to a dance.’

This, perhaps, is due to whispered words being perceived by
their sounds rather than their sense and meaning.

Communications can fail when one or the other party is not
listening or is being distracted. The man reading his paper at
breakfast, muttering and nodding without really listening to his
wife’s conversation.

Where distance or an interval of time is involved, or the
message is complex, a written report should be made. It can be
referred ‘back to’ if it is difficult to remember and understood. In
itself it forms a record and may be a basis for other actions.

Written Reports

All written reports should be written as clearly and concisely as
possible for the intended reader. ‘Purpose’ type reports are
used where commercial policy and company control is used
within the organisation.

News Summaries

This is used within organisations to inform employees of
changes in company performance, safety issues, training
course information etc. It can be in the form of a Newsletter,
Magazine or a Notice on the bulletin board.

Body Language

Eye contact, facial expression, body orientation, hand and head
movement and physical separation are all ways w e
communicate without speaking. It can also affect our
relationships with and perception of the personality of the other
person. Body language conveys far more than speech alone.
Eye contact is usually very brief, except between the most
intimate of friends. Prolonged staring is seen as threatening
and should be avoided.

Facial expressions can convey a whole series of emotions,
sadness, delight, disgust, contempt, boredom and many more.
By observing the listener’s facial expression it soon becomes
apparent that you may have lost their interest or perhaps are
antagonising them.

Touch, except for a brief handshake, is not welcome in western
society; one tends to be suspicious of someone who clings to
your hand when introduced.

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Posture and whole body movement is a guide to the listener’s
interest. We tend to lean towards those with whom we agree
and away from those we dislike. When bored we avoid even
the briefest of eye contact or may display our disinterest by
drumming fingers or playing with a pencil.

We guard our personal space jealously, sitting or standing in
close proximity to other than intimate friends unsettles us. If
colleagues are sharing a desk, facing each other, they tend to
resent spill-over from their colleague’s side into what they see
as ‘their space’ and will move objects, openly or surreptitiously,
back to the other side.

Verbal communication can be altered by varying the pattern of
speech; by changing the pitch of our voice, stressing some
phrases or inserting pauses. A rising voice and rapid speech
may portray anxiety whilst short clipped speech may express
urgency. Rambling speech indicates uncertainty. The end of a
meaningful sentence, dropping the voice, eye contact and
possibly gestures are all clues to the completion of that
speaker’s turn and it is time for an input from another speaker.
An interruption can be taken as a threat. Most people, when
interrupted, will give way to avoid simultaneous speech. An
interruption is considered to break the rules and is seen as rude
and domineering.

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SECTION 2: WORKLOGGING & RECORDING

While it is generally regarded that English is the international
language of the aeroplane, it is not the language used
nationally. Manuals and documentation are provided in the
country of manufacture in the national language and are
adequate for use there. When such aircraft equipment is used
on the British register then the necessary written information
must be in English, Log Books also must be in English, foreign
language log books will be closed and retained with the records.
The information being provided by every organisation and
person associated with aircraft and equipment needs to be clear
and concise and free from ERROR. To this end training and
examination techniques produce certifiers who have
demonstrated the ability to communicate effectively in written
English!!!

This ability is used when communicating between individuals,
teams, companies and authorities from the ramp to the
boardroom. Lines of communications are created which ensures
the transmission of information to all parties, the most important
being how we communicate with our colleagues in the work
area. It is necessary to receive work instructions in writing from
whoever plans and schedules the work; this is usually
maintenance control in the form of workpacks. These will be
compiled from various sources, monitored by the department
and presented to the work team as a package. The progress of
the work can be accounted for only by strict adherence to the
rules laid down in company manuals with regard to use of the
workpack. Don’t do it your way, do it the Correct way!!

Documentation

The work layout on Job Cards and Work Sheets should
encourage work to be signed for as it progresses throughout the
stages. The design of the forms should be such that there are
full instructions available on how to complete the form with the
required information. Ambiguity should be avoided. The form
should be as simple as possible to achieve the results desired.
Any data for onward processing should be in a form which is
easy to use. The layout should leave ample space for recording
action.

Printing of forms should have letters and numbers of a size that
is easily read, without the danger of misreading due to poor
quality printing.

When recording work on the Job Cards and Work Sheets it shall
be in accordance with the approved maintenance manual text,
and all references made in accordance with the manual
numbering system. This also applies to work in accordance with
Service Bulletins, Airworthiness Directives and Airworthiness
Notices etc. There should be NO RELYING ON MEMORY or
referring to unauthorised books i.e. using training notes.
Routine tasks and major components changes usually have
pre-printed work sheets, with the job laid down in stages for
certification signatures. Non-routine tasks, such as repair and
rectification has to rely on the licensed engineer completing the
work sheets as the job progresses in a logical, safe manner with
duplicate inspections and tasks correctly called up as required
by the task. The technical information used is only found in
approved publications and great care is needed to ensure these
are complete and up to date. It is the responsibility of the

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Certificate of Release to Service issuer to ensure this. Should
errors be found or suspected in Manuals, Drawings and CDs

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your company publications’ section should help you initially. If
problems still exist the Aircraft’s Customer Services Department
must be contacted.

The certifying engineer should also be up to date with Company
Procedures and report discrepancies through the usual
channels. He should be aware of his responsibilities and duties
in accordance with the ANO, EASA’s and AWN No 3, with
paragraph 1:15 in mind constantly.

DO NOT ASSUME - CHECK!!

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SECTION 3: KEEPING UP TO DATE, CURRENCY UPDATING

All aircraft engineers have to be UP TO DATE with the latest
service bulletins, letters and amendments to Manuals etc. This
awareness of changes can be brought to the attention of
engineers by safety notices on the company notice boards and
by passing copies of the amendments around to be read. The
company’s Quality Assurance Department probably will require
signatures of proof, that the engineer has read those important
amendments which are applicable to him. Outside the direct
changes to the aircraft the engineer is currently certificating, he
should be kept up to date with changing technology modern
techniques.

Reading commercial aircraft periodicals, watching technical
programmes on television and downlo ading technical
information from the Internet, help in the process of keeping
abreast of new developments in the industry. If the new
techniques and technology is going to be required in the near
future by the company, the engineers will be sent for specialist
courses, seminars and briefings etc.

One of the biggest causes of aircraft accidents and incidents
which can be attributed to engineers is the incorrect assembly
of components. This can be due to engineers’ carrying out work
without reading the Manuals and other technical information,
perhaps they are reverting to memory, We have also heard the
term ‘if all else fails, read the instructions’, and many people
dealing with technology have used this approach from time to
time. This is WRONG; the CORRECT thing to do is to read the
manuals FIRST! Not only the Aircraft Maintenance Manuals, but
the Service Bulletins, Illustrated Parts Catalogue, the pre-
printed job cards for the task in hand and any other information
required BEFORE you start the job.

The literature supplied to support the operation of the aircraft
should contain all the information you need. If it doesn’t contact
the publication section of your company or contact the
Aircraft/Component Manufacturer direct. If the correct
information cannot be found straight away, the work on the
aircraft/equipment should STOP until it is available.

Reading Manuals during ‘slack periods’ will help with your
subject knowledge and ease of referral in the future.

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SECTION 4: DISSEMINATION OF INFORMATION

In the maintenance of aircraft, over their life, information has to
pass between the Manufacturers’ Regulatory Bodies, Operators
and the Licensed Aircraft Engineers. Dissemination means
spreading information broad and this information can be passed
on by several methods. The information may be of a GENERAL
OR TECHNICAL nature, not requiring any certifying action by
an individual engineer. The Civil Aviation Authority disseminates
information of an Airworthiness Technical and General nature to
all pilots, airfield ranges operators and licensed engineers, by
their publication CAP 455 Airworthiness Notices.

Where information is required for the certification of aircraft by
the individual, the information will be written in a format he
should be capable of understanding. This information will be
Service Bulletins, Letters, and Amendments to Manuals etc.

Incoming information will be disseminated, by circulars, notice
board bulletins posters, charts, photographs, videos and films.
Short, precise and urgent messages to groups could be
conveyed by telephone and public address systems.

If the information is very important and has a safety aspect,
feedback is required. All those who have a need to know, have
received the information and that they understand it is shown by
signing an attached action slip. When completed it will give
evidence that all those who need to know have been made
aware of the new/changes of information.

The Licensed Aircraft Engineer should be made aware of all
Service Bulletins, Letters, Manual Amendments, Airworthiness
Directives and Airworthiness Notices for those
aircraft/components that he is certifying serviceable for Release
to Service.

The engineer, when he becomes aware of the problem, has a
duty to share his knowledge with others. Directly to his peers
verbally, and management within his company, perhaps
following a laid down in-house reporting system.

As highlighted earlier, both the individual engineer and the
organization in which he works have a shared responsibility to
keep abreast of new information. Good dissemination of
information within an organization forms part of its safety
culture. Typically, the maintenance organization will be the
sender and the individual engineer will be the recipient.

An aircraft maintenance engineer or team of engineers need to
plan the way work will be performed. Part of this process should
be checking that all information relating to the task has been
gathered and understood. This includes checking to see if there
is any information highlighting a change associated with the
task (e.g. the way something should be done, the tools to be
used, the components or parts involved)

There should normally be someone within the maintenance
organization with the responsibility for disseminating
information. Supervisors can play an important role by ensuring
that the engineers within their team have seen and understood
any communicated information.

Communication is an active process whereby both the
organization and engineer have to play their part. It is
imperative that engineers working remotely from the
engineering base (e.g. on the line) familiarize themselves with

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new information (on notice boards, in maintenance manuals,
etc.) on a regular basis.

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Poor dissemination of information was judged to have been a
contributory factor to the Eastern Airlines accident in 1983. The
NTSB accident report stated:

“On May 17, 1983, Eastern Air Lines issued a revised work card
7204 [master chip detector installation procedures, including the
fitment of O-ring seals]… The material was posted and all
mechanics were expected to comply with the guidance.
However, there was no supervisory follow-up to insure that
mechanics and foremen were incorporating the training material
into the work requirements… Use of binders and bulletin boards
is not an effective means of controlling the dissemination of
important work procedures, especially when there is no
accountability system in place to enable supervisors to ensure
that all mechanics had seen the applicable training and
procedural information.”

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Human Factors
Chapter 8
HUMAN ERRORS

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Contents
SECTION 1: ERROR MODELS AND THEORIES ---------------------------- 1
1.1 DESIGN VERSUS OPERATOR-INDUCED ERRORS -------------------- 1
1.2 VARIABLE VERSUS CONSTANT ERRORS ------------------------------- 1
1.3 REVERSIBLE VERSUS IRREVERSIBLE ERRORS ------------------------ 2
1.4 SLIPS, LAPSES AND MISTAKES ------------------------------------------- 4
1.5 SKILL-, RULE- AND KNOWLEDGE-BASED BEHAVIOURS AND
ASSOCIATED ERRORS ---------------------------------------------------------- 6
1.6 THE ‘SWISS CHEESE MODEL’ -------------------------------------------- 8
1.7 TYPES OF ERROR IN MAINTENANCE TASKS ------------------------- 10
1.8 ERRORS DURING REGULAR AND LESS FREQUENT
MAINTENANCE TASKS -------------------------------------------------------- 10
1.9 VIOLATIONS ---------------------------------------------------------------- 11
1.10 HUMAN FACTORS INCIDENT INVESTIGATION -------------------- 13
1.11 LACK OF Communication ---------------------------------------------- 16
1.12 COMPLACENCY ---------------------------------------------------------- 16
1.13 LACK OF KNOWLEDGE -------------------------------------------------- 16
1.14 DISTRACTION ------------------------------------------------------------- 17
1.15 LACK OF TEAMWORK --------------------------------------------------- 19
1.16 FATIGUE ------------------------------------------------------------------- 19
1.17 LACK OF RESOURCES --------------------------------------------------- 19
1.18 PRESSURE ----------------------------------------------------------------- 20
1.19 LACK OF ASSERTIVENESS ---------------------------------------------- 20
1.20 STRESS --------------------------------------------------------------------- 21
1.21 LACK OF AWARENESS -------------------------------------------------- 21
1.22 Norms---------------------------------------------------------------------- 22
1.23 SAFETY NETS ------------------------------------------------------------- 22
1.24 Functional Checks ------------------------------------------------------ 27
SECTION 2: TYPES OF ERROR IN MAINTENANCE TASKS ------------ 28
SECTION 3: IMPLICATIONS OF ERRORS --------------------------------- 30
SECTION 4: AVOIDING AND MANAGING ERRORS ------------------- 31
4.1 THE PRINCIPLES OF ERROR MANAGEMENT ----------------------- 33
4.2 SUMMARIZING THE EM PRINCIPLES --------------------------------- 37

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SECTION 1: ERROR MODELS AND THE ORIES

To appreciate the types of error that it is possible to make,
researchers have looked at human error in a number of ways
and proposed various models and theories. This attempt to
capture the nature of the error and its characteristics. To
illustrate this, the following models and theories will be briefly
highlighted:

 Design- versus operator-induced errors

 Variable versus constant errors

 Reversible versus irreversible errors

 Slips, lapses and mistakes

 Skill-, rule- and knowledge-based behaviours and
associated errors

 The ‘Swiss Cheese Model’

1.1 DESIGN VERSUS OPERAT OR-INDUCED ERRORS

In aviation, emphasis is often placed upon the error(s) of the
front line operators, who may include flight crew, air traffic
controllers and aircraft maintenance engineers. However, errors
may have been made before an aircraft ever leaves the ground
by aircraft designers. This may mean that, even if an aircraft is
maintained and flown as it is designed to be, a flaw in its original
design may lead to operational safety being compromised.
Alternatively, flawed procedures put in place by airline,
maintenance organization or air traffic control management may
also lead to operational problems.

It is common to find when investigating an incident or accident
that more than one error has been made and often by more
than one person. It may be that, only when a certain
combination of errors arises and error ‘defences’ breached (see
the ‘Swiss Cheese Model’) will safety be compromised.

1.2 VARIABLE VERSUS CONS TANT ERRORS

In his book “Human Error”, Professor Reason discusses two
types of human error: variable and constant. It can be seen in
Figure 3.1 that variable errors in (A) are random in nature,
whereas the constant errors in (B) follow some kind of
consistent, systematic (yet erroneous) pattern. The implication
is that constant errors may be predicted and therefore
controlled, whereas variable errors cannot be predicted and are
much harder to deal with. If we know enough about the nature
of the task, the environment it is performed in, the mechanisms
governing performance, and the nature of the individual, we
have a greater chance of predicting an error.

However, it is rare to have enough information to permit
accurate predictions; we can generally only predict along the
lines of “re-assembly tasks are more likely to incur errors than
dismantling tasks”, or “an engineer is more likely to make an
error at 3 a.m., after having worked 12 hours, than at 10 a.m.
after having worked only 2 hours”.

It is possible to refine these predictions with more information,
but there will always be random errors or elements which
cannot be predicted.

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1.3 REVERSIBLE VERSUS IR REVERSIBLE ERRORS

Another way of categorizing errors is to determine whether they
are reversible or irreversible. The former can be recovered from,
whereas the latter typically cannot be. For example, if a pilot
miscalculates the fuel he should carry, he may have to divert to
a closer airfield, but if he accidentally dumps his fuel, he may
not have many options open to him.

A well designed system or procedure should mean that errors
made by aircraft maintenance engineers are reversible. Thus, if
an engineer installs a part incorrectly, it should be spotted and
corrected before the aircraft is released back to service by
supervisory procedures in place.

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Target patterns of 10 shots fired by two riflemen. Rifleman A’s pattern exhibits no
constant error, but large variable errors; rifleman B’s pattern exhibit’s a large constant
error but small variable errors. The latter would, potentially, be easier to predict and to
correct (e.g. by correctly aligning the rifle sight).

Fig 3.1 Variable versus Constant Errors

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1.4 SLIPS, LAPSES AND MISTAKES

Reason highlights the notion of ‘intention’ when considering the
nature of error, asking the questions:

 Were the actions directed by some prior intention

 Did the actions proceed as planned?

 Did they achieve their desired end?

Reason then suggests an error classification based upon the
answers to these questions as shown in Figure 3.2.

The most well-known of these are slips, lapses and mistakes.
Slips typically occur at the task execution stage, lapses at the
storage (memory) stage and mistakes at the planning stage.
Slips can be thought of as actions not carried out as intended or
planned, e.g. ‘transposing digits when copying out numbers, or
misordering steps in a procedure.

Lapses are missed actions and omissions, i.e. when somebody
has failed to do something due to lapses of memory and/or
attention or because they have forgotten something, e.g.
forgetting to replace an engine cowling.

Mistakes are a specific type of error brought about by a faulty
plan/intention, i.e. somebody did something believing it to be
correct when it was, in fact, wrong, e.g. an error of judgment
such as mis-selection of bolts when fitting an aircraft
windscreen.

Violations sometimes appear to be human errors, but they
differ from slips, lapses and mistakes because they are
deliberate ‘illegal’ actions, i.e. Somebody did something
knowing it to be against the rules (e.g. deliberately failing to
follow proper procedures). Aircraft maintenance engineers may
consider that a violation is well intentioned, i.e. ‘cutting corners’
to get a job done on time. However, procedures must be
followed appropriately to help safeguard safety.

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Fig 3.2 Error types based on intention

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1.5 SKILL-, RULE- AND KNOWLEDGE -BASED
BEHAVIOURS AND ASSOC IATED ERRORS

The behaviour of aircraft maintenance engineers can be broken
down into three distinct categories: skill-based, rule-based and
knowledge-based behaviour. Each of these behaviour types
have specific errors associated with them.

Examples of skill-based errors are action slips, environmental
capture and reversion. Action slips as the name implies are the
same as slips, i.e. An action not carried out as intended. The
example given in Figure 3.3 may consist of an engineer
realizing he needs a certain wrench to complete a job but,
because he is distracted by a colleague, picks up another set to
the wrong torque and fails to notice that he has tightened the
bolts incorrectly.

Environmental capture may occur when an engineer carries out
a certain task very frequently in a certain location. Thus, an
engineer used to carrying out a certain maintenance adjustment
on an Airbus A300, may inadvertently carry out this adjustment
on the next A300 he works on, even if it is not required (and he
has not made a conscious decision to operate the skill).

Reversion can occur once a certain pattern of behaviour has
been established, primarily because it can be very difficult to
abandon or unlearn it when it is no longer appropriate. Thus, an
engineer may accidentally carry out a procedure that he has
used for years, even though it has been recently revised. This is
more likely to happen when people are not concentrating or
when they are in a stressful situation. Green et al define these:

“Skill-based behaviours are those that rely on stored routines or
motor programs that have been learned with practice and may
be executed without conscious thought. Rule-based behaviours
are those for which a routine or procedure has been learned.
The components of a rule-based behaviour may comprise a set
of discrete skills. Knowledge-based behaviours are those for
which no procedure has been established. These require the
[aircraft maintenance engineer] to evaluate information, and
then use his knowledge and experience to formulate a plan for
dealing with the situation.”

Rule-based behaviour is generally fairly robust and this is why
the use of procedures and rules is emphasized in aircraft
maintenance. However, errors here are related to the use of the
wrong rule or procedure. For example, an engineer may
misdiagnose a fault and thus apply the wrong procedure, thus
not clearing the fault. Errors here are also sometimes due to
faulty recall of procedures. For instance, not remembering the
correct sequence when performing a procedure.

Errors at the knowledge-based performance level are related to
incomplete or incorrect knowledge or interpreting the situation
incorrectly. An example of this might be when an engineer
attempts an unfamiliar repair task and assumes he can ‘work it
out’. Once he has set out in this way, he is likely to take more
notice of things that suggest he is succeeding in his repair,
while ignoring evidence to the contrary (known as confirmation
bias).

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Fig 3.3 Example of an Action Slip

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1.6 THE ‘SWISS CHEESE MO DEL’

In his research, Reason has highlighted the concept of
‘defences’ against human error within an organization, and has
coined the notion of ‘defences in depth’. Examples of defences
are duplicate inspections, pilot pre-flight functional checks, etc.,
which help prevent to ‘trap’ human errors, reducing the
likelihood of negative consequences. It is when these defences
are weakened and breached that human errors can result in
incidents or accidents. These defences have been portrayed
diagrammatically, as several slices of Swiss cheese (and hence
the model has become known as Professor Reason’s “Swiss
cheese” model) (see Figure 3.4).

Some failures are latent, meaning that they have been made at
some point in the past and lay dormant. This may be introduced
at the time an aircraft was designed or may be associated with
a management decision. Errors made by front line personnel,
such as aircraft maintenance engineers, are ‘active’ failures.
The more holes in a system’s defences, the more likely it is that
errors result in incidents or accidents, but it is only in certain
circumstances, when all holes ‘line up’, that these occur.
Usually, if an error has breached the engineering defences, it
reaches the flight operations defences (e.g. in flight warning)
and is detected and handled at this stage. However,
occasionally in aviation, an error can breach all the defences
(e.g. a pilot ignores an in flight warning, believing it to be a false
alarm) and a catastrophic situation ensues.

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Fig 3.4 Reason’s Swiss Cheese Model

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1.7 TYPES OF ERROR IN MAINTENANCE TASKS

As aircraft maintenance engineers are human, errors in the
industry are inevitable. Any maintenance task performed on an
aircraft is an opportunity for human error to be introduced.
Errors in aircraft maintenance engineering tend to take two
specific forms:

 An error that results in a specific aircraft problem that
was not there before the maintenance task was initiated;

 An error that results in an unwanted or unsafe condition
remaining undetected while performing maintenance
task designed to detect aircraft problems, i.e. something
is missed.

Examples of errors highlighted in the above (I) are incorrect
installation of line replaceable units, failure to remove a
protective cap from a hydraulic line before reassembly or
damaging an air duct used as a foothold while gaining access to
perform a task.

Examples of errors in (ii) are a structural crack unnoticed during
a visual inspection task or a faulty avionics box that remains on
the aircraft because incorrect diagnosis of the problem led to
removal of the wrong box.

1.8 ERRORS DURING REGULA R AND LESS FREQUENT
MAINTENANCE TASKS

A large proportion of maintenance tasks are fairly routine, such
as regular, periodic checks on aircraft. Thus, engineers will use
a certain set of procedures relatively frequently and, as noted in
the previous section, slips and lapses can occur when carrying
out procedures in the busy hangar or line environment.
“Repetitive Tasks” noted that engineers will often become so
accustomed to doing a regular, often repeated task, that they
will dispense with written guidance altogether. It would be
unrealistic and unnecessarily time consuming to expect them to
constantly refer to familiar guidance material. However, errors
may occur if they do not keep up-to-date with any changes that
occur to these frequently used procedures. These routine tasks
are also prone to complacency, environmental capture and rule-
based errors.

When undertaking less frequently performed tasks, there is the
possibility of errors of judgment. If the engineer does not
familiarize or re-familiarise himself properly with what needs to
be done, he may mistakenly select the wrong procedure or
parts.

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1.9 VIOLATIONS

It is an unfortunate fact of life that violations occur in aviation
maintenance. Most stem from a genuine desire to do a good
job. Seldom are they acts of vandalism or sabotage. However,
they represent a significant threat to safety as systems are
designed assuming people will follow the procedures. There are
four types of violations:

 Routine violations

 Situational violations

 Optimising violations

 Exceptional violations

Routine violations are things which have become ‘the normal
way of doing something’ within the person’s work group (e.g. a
maintenance team). They can become routine for a number of
reasons:

Engineers may believe that procedures may be over
prescriptive and violate them to simplify a task (cutting corners),
to save time and effort. Examples of routine violations are not
performing an engine run after a borescope inspection (“it never
leaks”), or not changing the ‘O’ seals on the engine gearbox
drive pad after a borescope inspection (“they are never
damaged”).

Situational violations occur due to the particular factors that
exist at the time, such as time pressure, high workload,
unworkable procedures, inadequate tooling, and poor working
conditions. These occur often when, in order to get the job
done, engineers consider that a procedure cannot be followed.
An example of a situational violation is an incident which
occurred where the door of a B747 came open in-flight. An
engineer with a tight deadline discovered that he needed a
special jig to drill off a new door torque tube. The jig was not
available, so the engineer decided to drill the holes by hand on
a pillar drill. If he had complied with the maintenance manual he
could not have done the job and the aircraft would have missed
the service.

Optimising violations involve breaking the rules for ‘kicks’.
These are often quite unrelated to the actual task. The person
just uses the opportunity to satisfy a personal need. An example
of an optimising violation would be an engineer who has to go
across the airfield and drives there faster than permitted

Exceptional violations are typified by particular tasks or
operating circumstances that make violations inevitable, no
matter how well intentioned the engineer might be.

Time pressure and high workload increase the likelihood of all
types of violations occurring. People weigh up the perceived
risks against the perceived benefits; unfortunately the actual
risks can be much higher.

Maintenance errors are, unfortunately, not some new
phenomenon, but with the advent of more reliable aircraft and
Cockpit Resource Management for pilots, the maintenance
component as the cause of an aircraft accident has become
more noticeable.

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May 25, 1979. As an American Airlines DC10 rotated to lift off
at Chicago’s O’Hare Airport, the left engine fell off and crashed
back onto the runway. Thirty-one seconds later 273 persons
would be dead from maintenance error. This accident was
directly attributed to ‘improper maintenance procedures’ which
led to the failure of the pylon structure. Engines were being
fitted with a fork lift as a ‘short cut’ damaging the pylon structure
and management were aware that this procedure was being
used. When the accident was investigated, little was done to
look at the human factors that led up to the accident. Instead,
attention was focused on the systems which had failed.

The accidents in the Hawaiian Islands with the Boeing 737
fuselage ripping open and the cockpit window blowing out on
the BAC1-11 in England made human factors part of the
accident investigation.

In Canada, on 10 March 1989, an F-28 crashed killing 24
people. While maintenance didn’t directly because the
accident, it was determined that it was a contributing factor.
Had maintenance not made an error the accident would likely
not have occurred? As the result of this accident Mr Gordon
Dupont, then working for Transport Canada, was tasked to
develop a training programme which could help reduce the
possibility of maintenance errors being made.

Education on how Human Factors affect our judgement and
performance is only one of the key parts in the fight to reduce
maintenance error. At present we are asking Aircraft
Maintenance Engineers to avoid making a human error without
giving them the training to do so. Most companies have come
to realise that some form of human factors training is needed to
reduce maintenance error in their company.

Unfortunately, this realisation all too often occurs after an
aircraft incident or accident such as an aircraft falling off jacks in
the hangar. Some people feel accidents are inevitable as part
of the business of aircraft operation. They find the guilty person
and suspend or fire him. They continue their operations in the
same manner until the same or another error occurs. Often the
best workers are fired – a worker who will most likely never
make that particular error again.

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1.10 HUMAN FACTORS INCIDE NT INVESTIGATION

By the Certification, Documentation and Recording we have
become very proficient at tracing the history of aircraft
components. This has resulted in our being able to monitor the
lives of components within systems, to extend their lives for
overhaul and to increase the reliability of the aircraft. We can
extend the useful life of a component knowing from past history
that it is unlikely to fail. This has worked so well in aircraft
safety that human factors are of the most likely causes of failure
to come to the foreground.

We therefore now need to record and trace the history of our
human errors. We know from Heinrich’s ratio that there are
about 600 incidents for every fatal accident.



The Heinrich ratio

The accidents are the logical result of many incidents. If we
record and reduce the number of incidents we will be on our
way to reducing the number of accidents, especially fatal ones.
This will call for a ‘human factors’ investigation to every
significant incident which occurs. A threshold must be set and
the investigators must be ready and able to find the ‘root
causes’ of the incident. By threshold we mean, at what point do
we investigate? The aircraft on the hangar floor is obvious, but
some criteria must be set which triggers the investigation. This
threshold level can be moved up or down at a later date as
required.

Ideally the investigation team have been trained in human
factors and are well known and trusted by the employees. The
facts should be reported both to management and employees;
trust is a big factor. The findings and recommendations of the
report should have a wide distribution and ACTED UPON where
required. The INSTIGATOR of the Incident should be PART OF
THE SOLUTION.

Let us now consider the Latent Conditions/Preconditions
identified by Gordon Dupont as THE DIRTY DOZEN. These
are the 12 most common causes of latent failures identified.
There are certainly more than this, but these 12 causes occur
most frequently.

It is a fact that people do not commit errors intentionally unless
they are suffering from a psychological disorder. We therefore
must expect that all errors are the result of mistakes which
occur naturally in all humans, as a matter of course. To help us
reduce the frequency of errors we must recognise the factors
which cause them and also provide the necessary
SAFEGUARDS. These are known as SAFETY NETS.

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THE DIRTY DOZEN
(Common Causes of Judgement Interference)

1 LACK OF COMMUNICATION
2 COMPLACENCE
3 LACK OF KNOWLEDGE
4 DISTRACTION
5 LACK OF TEAMWORK
6 FATIGUE
7 LACK OF RESOURCES
8 PRESSURE
9 LACK OF ASSERTIVENESS
10 STRESS
11 LACK OF AWARENESS
12 NORMS

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1.11 LACK OF COMMUNICATIO N

Communication is vital in an aviation environment. We carry out
our work in accordance with the Aircraft Maintenance Manual.
We need to be up to date with service bulletins. At shift changes
we need to be able to effectively communicate with the next
shift any outstanding tasks that need to be progressed.

If there is a lack of effective communication between shifts then
items may get missed and aircraft may be released to service
with components not fitted or fitted incorrectly.

1.12 COMPLACENCY

Complacency often occurs when carrying out a frequent routine
inspection to find a fault. This check, having been completed
frequently, and not finding a fault, will lead to the engineer
changing his attitude, and he will say ‘I HAVE NEVER EVER
COME ACROSS A FAULT ON THAT INSPECT’ . Next time he
carries out the inspection he will look and not see the fault. He
might be tempted, when under the pressure of time to ‘Sign Up’
without actually carrying out the scheduled inspection.
Complacency can be due to a character defect. Here the
individual will show signs of over-confidence, self-satisfaction,
boredom and not being dedicated to the task. A careless
attitude could develop over time and be infectious to other
employees. The actions of the complacent individual may be
hidden until an accident/incident occurs.

1.13 LACK OF KNOWLEDGE

If you do not know, ASK! – Or find out from approved sources;
i.e. Manuals and Schedules. To proceed in ignorance is a
criminal act which will end in disaster. It is not a bad reflection
on you not to know; as everyone goes through this phase in
following a learning curve, if it is inevitable that lack of
knowledge will stop the job, so be it. Stop the job until the level
of knowledge required to proceed is available, and this may be
obtained from a variety of sources. For example, in large
maintenance organisations a Technical Services Department,
manned round the clock, can be contacted when technical
support is required, station engineers in remote corners of the
world are often in contact with Technical Services Departments
on a daily/hourly basis.

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1.14 DISTRACTION

Interruption to a flow of well thought out actions is a common
occurrence that normally does not produce a problem. We are
continually distracted by outside influences in almost everything
we do and in some cases these go almost unnoticed. The
effects of problem solving in puzzles, quizzes and mental
competitions are usually rewarding in raising our self-esteem
and in giving an inner glow of achievement, but would this be
the case when confronted by a result that is not satisfactory?
Lack of attention to detail, brought about by continual
interruption will cause this. No self-esteem here, in fact the very
opposite effect would be seen; frustration and anger would be
more likely.

This is the outcome of interruption of the thought process when
any sequences of work actions are taking place. Frustration
can lead to anger which, in turn, clouds our ability to build the
mental pictures necessary to see the task progressing ahead of
the actual stage the work is at. It also leads to forgetfulness; a
stage of work left out of the sequence will break the chain and if
not corrected, will most certainly lead to a national headline. To
guard against interruptions we must plan ahead. First identify
the Interrupter and the Interrupted.

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THE
INTERRUPTER
can be any factor which causes a
judgement interference.
FOR EXAMPLE: 1. An unplanned change to a work
schedule, or procedure, brought about
by a change in priority somewhere
else, ‘You are needed elsewhere,
drop that and attend to that over
there’.

2. ‘Telephone call for you, I think it’s a
domestic matter’.

3. A change in the sequence of events
during a work stint, ‘Go to lunch
early and cover for …….’.

4. Visitors who discuss forthcoming
social arrangements or last night’s TV.

Awareness of the effects of being the
interrupter is essential if we are to avoid
doing it. Weigh up the potential
consequences of judgement interference
on someone’s work; do not encourage
him to drop his safety net, by having him
listen to you.

The rule should be:

KEEP TRIVIAL THINGS AWAY FROM A
PERSON OR GROUP ENGAGED IN
AIRWORTHINESS MATTERS.

THE
INTERRUPTED

If a choice of working environment is
given the possibility of disturbance should
be considered before starting. When a
choice is not possible then careful
planning may be needed to avoid it. One
method is to plan the working area with
access and exit points which discourage
casual walk through by passing traffic.
This can be done by partitions and walls
which divide the work area into stations or
work bays and which allow people to walk
by without direct visual contact being
made. On aircraft maintenance, a system
of controlled access to certain zones is
usually built into the requirements of the
approved maintenance schedule, which
ensures that different trades access one
zone at different times, thereby reducing
interference.

When interrupted and then returning to
the task, GO BACK THREE STEPS
BEFORE GOING FORWARD AGAIN .
This will help prevent an error being
made. The human mind is always thinking
ahead when problem solving.

‘Why do we always leave the original
on top of the photocopier?’

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1.15 LACK OF TEAMWORK

Teamwork provides a reasonable environment for the majority
of maintenance engineers to operate in, and is often described
as a comfort zone. This zone is an area where the collective
expertise will conceal the technical inadequacies of the few.
This leads to distrust by many engineers who have had many
years of experience working on their own, making their own
judgements and sometimes their own mistakes. They will now
be unwilling to embrace the idea of Teamwork. But when
confronted by job changes or changes in the Management of
Maintenance Organisation, they will become aware of the
benefits of the collective decisions that come from Team
working. A more altruistic attitude from the experienced
engineers should help prevent an error being made by the junior
inexperienced members of the team.

The leader of the team, whilst maintaining discipline, should
keep the task progressing in the right direction combining the
different levels of skill with a well motivated team. Each member
likes to feel that his contribution to the effort is valued especially
the weaker ones. The leader will be instrumental in seeing this
happens, which in turn encourages the whole team. The
collective final result will be felt by each individual member of
the team. If this teamwork is lacking, the output, performance
and reliability will be poor, motivation and self-esteem will be
degraded. The team not working together, helping and checking
on each other’s work removes a safety net in aircraft
maintenance.

1.16 FATIGUE

The onset of fatigue is slow and unnoticed and is not a factor
that is given much importance. However, it is a big factor,
contributing, when combined with other latent and active errors,
to produce an accident.

Fatigue can be due to many factors such as lack of sleep, food
and physical effort, previously discussed in Module 3.

Most accidents described in the Introduction can be traced back
to an error made during a night shift when the arousal levels
and circadian rhythms are low and the engineer responsible
was fatigued. Perhaps manning levels, shift patterns and hours
worked will now become more important in the investigation of
maintenance errors.

1.17 LACK OF RESOURCES

Commercial Pressures are felt by all companies that have to
make a profit otherwise they do not survive. Competition affects
the price a company can charge for its services – the customer
can always go elsewhere. So pressure is on to CUT
CORNERS. This can be by keeping wages low, but the staff
morale is low and there will be a large turnover in staff numbers.
Keeping the numbers of staff low, i.e. 8 instead of 10 on a shift,
results in overwork, fatigue and again low morale. Low levels of
spares could create pressures not to change a component
when it really needs to be. Lack of tools and equipment required
to maintain aircraft increases the chance of mistake to make by
a now increasingly frustrated engineer.

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1.18 PRESSURE

Time Pressures are often applied at all levels in an organisation
by management. Errors are inevitable if a person or group are
working to deadlines that are unrealistic. Errors may occur in
part of a procedure that the person recognises as an error, but if
the pressure is high enough to complete the task, that person
may not correct them. He may ‘let it go’ even though it is
obvious that the job is not correct.

Companies should have correct staffing levels with the correct
levels of expertise. A planning department should help with
scheduled workloads; guide and advice for the completion time
on unscheduled maintenance tasks. Commercial pressures as
previously described put pressures on the certifying engineer
due lack of resources. Pressure can be applied on aircraft
manufacturers, operators and maintainers by the Regulating
Bodies. However, it has been known for the pressure to be
applied in reverse, in some countries. A manufacturer has put
pressure on its regulatory body not to have a mandatory
instruction after a minor incident, but a potentially serious one
for one of their aircraft. The event happened again with a major
loss of life. The cargo bay door of a DC10 opened in flight over
France. Pressure can be felt by the individual when he
recognises his lack of knowledge and experience. This should
also be recognised by management when matching the man to
the task to prevent an error being made. The inexperienced
engineer should ‘stand up’ and tell management when he feels
unsafe in carrying out the task delegated, not muddling on
producing a possible hidden fault.

1.19 LACK OF ASSERTIVENES S

Being Assertive is when a person strongly declares or insists on
his opinion, will, intent, plan or method of completing a task,
upon his peers and/or subordinates. It should be carried out,
without showing aggression and offering physical violence.
Logical argument, demonstration of superior knowledge and
skill, with the perception of a great deal of experience, will
usually be sufficient for that person to ‘get his way’. Lack of
assertiveness can occur when a person is unsure of his own
skill, knowledge and position in the ‘pecking order’ of a team,
group or hierarchy. The opinion of this person could be easily
swayed and he may be forced to carry out tasks, then certificate
them against an inner self-doubt of its correctness. He may be
cajoled into signing for a known error (‘It’ll be alright till next
time’). The unsure unassertive person is likely to work on and
around a problem, not admitting he has a problem which would
show his lack of knowledge and skill. These dangerous
situations will eventually lead to an accident.

There are times when we have to be assertive to prevent
becoming overloaded with work, unfairly, both physically and
mentally. The unassertive engineer with a CAN DO attitude will
be inadvertently making a rod for his own back. Coupled with
fatigue, he will eventually make a mistake, which could end up
as a catastrophe.

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1.20 STRESS

Stress is very difficult to measure; it affects different people at
different times and by differing types of stress. The effects may
be cumulative and can be related to:

 Psychological Health
 Physical Health
 The Environment
 The Job in Hand
 The Organisation/Management

How each of these five conditions may be expanded and can be
found in Module 3.

The stressed individual may be working away, with his peers
not noticing that he has a problem. His level of concentration
and mental performance might be such that he might make an
error which he was not conscious of making and it could lie
hidden until some future incident/accident.

It is the duty of the engineer NOT to sign/certify aircraft
documentation if he is aware of physical or psychological ill
health.

It is the duty of the Company to provide a working environment
such that the employee is not continually over-stressed.

Again stress can couple with other latent conditions to be part of
an accident.

1.21 LACK OF AWARENESS

The dictionary definition of Awareness is that the person is
‘informed and conscious of the ‘world’ around him’.

The lack of awareness must then imply a lack of information or
the inability to take in and ‘digest’ the information.

Lack of knowledge and lack of experience required by the job
position within an organisation, will place the occupant of that
position under pressure. Often the problem is not in the
textbooks and an ‘old head’ will use his vast experience to come
to a new solution to the new problem.

A skilled, able person will still be defeated if there is breakdown
in communications within his organisation. Poor passage of
information and feedback both up and down in a company is
going to cause a loss of important facts/data, leading to a lack
of awareness in making possible important decisions. These
failures can be due to poor use of verbal and written methods of
communications. For example – poor printing, layout and
diagrams in manuals with ambiguities in the text, together with a
failure to keep the manuals up to date by amendment action.

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1.22 NORMS

In any organisation there will be company expositions,
engineering organisational manuals, aircraft maintenance
schedules and manuals to direct and explain the correct
procedures and methods on how aircraft maintenance is to be
carried out. However, very often experienced engineers notice
and develop ‘short cuts’ in the laid down procedures. Often
these are of a result of pressures of time and manpower
shortages within the organisation. These ‘wrinkles’ of a quicker
easier way of doing a job, get passed on to other engineers.
The inexperienced engineer, seeing these short cuts as the
normal (Norm) way to carry out the task will not recognise any
pitfalls or other dangers. Often this problem is accentuated by
the failure to read the manuals and service bulletins each time
before starting the job. The laid down procedure is ignored and
forgotten. Management can often turn a blind eye when short
cuts are saving them time and trouble. Eventually, however,
one day this unapproved action will result in an
incident/accident.

For example – The DC10 crash at Chicago’s O’Hare Airport in
1979 due to incorrect methods of engine
installation.

1.23 SAFETY NETS

With all the above ‘dirty dozen’ there are things we can do to
prevent them leading to errors. These are the safety nets and
by following them we will reduce the likelihood of making
mistakes.

Lack of Communication

Use log books, worksheets, etc to record all work that has been
completed. If there are several stages on a worksheet, sign
each task as it is completed, don’t be tempted to ‘paper whip’ by
signing each page as a complete block.

At shift change, write a list of all outstanding jobs that need to
be completed and discuss this list with the oncoming shift to
remove any doubt as to what is required.

Complacency

Always train yourself to expect to find a fault. Even if you have
carried out the same job many times before, without finding a
fault, don’t think that you will never find one.

At every inspection, you should be expecting a fault to be
present.

Never sign for anything you have not done. If you don’t inspect
a certain area or component because you’ve never found
anything wrong before, don’t sign to say that you have
inspected it.

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Lack of Knowledge

If your knowledge of a particular aircraft or task is lacking then
get that knowledge. Get trained on the type of aircraft or system
you are dealing with.

Use up to date manuals and read them before doing any task.
If there is something you don’t understand then ask a more
experienced engineer for help. You should also have access to
your Company’s Technical Services department who will be
delighted to help, as will the technical representatives who are
present at most locations.

A lack of knowledge is not something to be ashamed of and
hidden, you should be constantly striving to improve your
knowledge level with regard to all aspects of you job.

Distraction

If you do get distracted in any way, try to finish the job you are
doing at the time before dealing with the distraction This is not
always possible, so in that case mark the uncompleted work so
that when you return you will know where you need to start
from.

Fit locking devices as you go, don’t leave all the wire-locking to
the end of the job, as it is more likely for one item to be
forgotten.

Make sure everything you do is double checked by yourself or
someone else to ensure that nothing has been missed.


Use a detailed worksheet and sign up as you complete each
task. When you return to the job, refer to the work sheet and go
back three steps so that you can be confident that nothing has
been missed.

Lack of Teamwork

Before a shift starts, discuss what needs to be done and
allocate the tasks fairly. Ensure that everyone understands what
they are doing and agrees with it.

If two of the shift wants to swap their assigned tasks with each
other, let them (providing there are no other reasons for making
the initial job allocation that they may not be aware of).

It can be good to try ‘team bonding’ exercises, whether it be
formally or informally. Team social gatherings help to create a
better team working environment, for instance.

Fatigue

Be aware of the symptoms of fatigue and look for them in
yourself and others.

Plan to avoid complex tasks at the bottom of your circadian
rhythm. This is the time to be doing the simple tasks.


Make sure that you sleep and exercise regularly. Remember,
the exercise does not have to be too strenuous – any form of
exercise that increases the heart rate is good for you.

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Lack of Resources

When an aircraft comes into the hangar for an inspection, check
suspect areas for any obvious defects before the inspection
starts. This will enable you to order stocks before they are
required.

Ensure that there is always an adequate stock of spares that
are required on a regular basis.

If there is another operator of the same aircraft as you at your
location, arrange to pool resources and have the facility to loan
spares and equipment.

Do not compromise your standards by fitting unserviceable
equipment or used consumables just to get the aircraft out on
time. If in doubt, ground the aircraft.

Pressure

Examine the pressure you are under to make sure that it is not
self-induced.

Communicate your concerns with your supervisor. He may be
able to remove some of the pressure you are under.

Ask for extra help. There may be other engineers working in a
different part of the hangar or other workshop who may be able
to assist you.

If the pressure is getting too much, just say no.

Lack of Assertiveness

Be strong. You are a highly trained and skilled engineer with
high standards. Refuse to let anybody force you to compromise
those standards

You cannot be forced to sign a release for an aircraft or
component if it is not serviceable. Just say no.

Stress

Be aware of the symptoms of stress and how it can affect your
performance.

If you are stressed, stop and look rationally at what is causing
the stress and look for ways of reducing it. Remember, the
amount of stress you experience depends on the demand that
you PERCEIVE is being placed on you and your PERCEIVED
ability.

Take the time to have a break from what you are doing. Have a
cup of coffee or go for a walk - anything to help you relax.

Don’t bottle up your stress – talk about it with your family,
friends, work colleagues or a professional counsellor. The old
adage is true – ‘A problem shared is a problem halved’

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Lack of Awareness

Before doing anything, take the time to think about what could
happen in every eventuality – no matter how unlikely the
scenario.

Check to make sure what you are doing will not conflict with an
existing modification or repair.

Ask others to check if they can see any potential problems that
you may have missed.

Norms

ALWAYS read the maintenance manual before carrying out any
servicing task. Work to the instructions it contains and nothing
else. If you can think of a better way to carry out the task,
suggest an amendment. Do not be tempted to use an
engineer’s ‘Little Black Book’.

It doesn’t matter how long a non-standard practice has been
used in your hangar with no problems – there is only one right
way to do a job and that is the maintenance manual way.

Active Failure

Latent conditions of failure may lie hidden, never to be
discovered until the pilot, engineer or ramp staff actually makes
a mistake ie. Human Error. If there are no safety nets in place
to help protect the individual and organisational system, they
will have an accident after already suffering many incidents. In
the CAA’s analysis of 230 Mandatory Occurrence Reports the
fundamental cause of occurrence was as follows:-

INCORRECT INSTALLATION 49%
INADEQUATE SERVICING 31%
DAMAGE DURING MAINTENANCE 4.5%
COMPONENT OVERHAUL ERROR 6.3%
CONSEQUENCE OF RECORDING ERROR 1.8%
NON-COMPLIANCE WITH REQUIREMENTS 7.3%

These figures are for the Operational Limitations but if analysed
for a Significant Reduction in Safety, incorrect installation rises
to 80%.

Here the engineer has brought all his latent failures and
problems to the sharp end of the business. Not fitting the
correct seal, part, locking device etc., or not fitting it in
accordance with the approved maintenance manual, service
bulletin, will be the active failure(s) and he will ultimately be
given the blame. When any Unsafe Act is made by any
individual involved with aircraft operations, we are probably well
on our way to an accident.

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Inadequate Safety Nets/Defences

It is a fact that, wherever people are performing tasks, however
skilled and conscientious they are, errors will still occur.

By the very nature of operating passenger transport aircraft,
everybody including the customer is aware and keen on the
need for safety. We therefore need measures in place to
protect from the consequences of human error. These can
include:

 Built-in redundancy and damage tolerance
 Special checks – duplicates
 Functional checks

Tolerance/Redundancy

Modern aircraft structures and systems are built to be failsafe,
having multiple load paths and redundancy by duplicating, even
replicating, the important systems. Components which are
critical, and do not have a duplicate to take up the load on
failure, will be given a SAFE Life. This will be stated by the
manufacturer after tests, such that the probability of failure will
be one in tens of millions and will be subject to stringent checks
and tests during its life. The design of Semi Monocoque
Construction in aircraft with its use of frames, longerons, spars,
ribs, intercostals and stringers, together with the stressed skin,
brings in a system that has multi-load paths to take up the load
in the failure of any member of this system. Together with tear
stoppers we will produce a structure that is resistant to crack
growth and is damage tolerant.

Most systems are also designed to be tolerant of error. If it is a
vital system like the powered flying controls using hydraulics
and electrics as their power sources, duplication is used. If a
tyre pressure is 5% out from what is specified, the performance
of the tyre will not be significantly affected. If the tyre blows on
a multi - wheeled landing gear unit, the loads will be taken by
the other wheels. The output from a generator may not be
exactly 200/115 volts, but components in the system will protect
itself from incorrect voltage and frequency.

These are a few examples of faults that show some tolerance to
failure, but should not be allowed if known, where there is little
tolerance to failure and where a single item could be
catastrophic, then special checks are called for.

Checks/Duplicate Inspections

Ideally no man should work alone and certify alone. Working in
pairs brings two pairs of eyes and two brains to the job,
checking on each other’s work for possible errors. Most
complex tasks involve stage inspections, usually making an
inspector supervising the mechanics and signing ‘over him’ for
the work carried out. It is the duty of the inspector to determine
the depth of supervision and inspection and what special
checks and tests are required at the stages determined by the
task. For example – when fitting a helicopter tail rotor hub
assembly onto the tail rotor gearbox, the index mark for a
master spine may be hidden after fitting; before closing a fuel
tank a cleanliness and loss article check should be carried out.
When working on critical systems, flying and engine controls the
regulating bodies such as the CAA, in the UK, require
DUPLICATE INSPECTIONS.

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The CAA also require, on certain aircraft, duplicate inspections
on designated VITAL POINTS. A duplicate inspection, ideally
independently, is an inspection first made by a qualified type
rated aircraft engineer and subsequently made by a second
qualified type rated engineer. The check is a repeat of the work
carried out by the first person. Duplicate inspections are
required after dismantling, reconnection and adjustment and are
designed to prevent INCORRECT INSTALLATION of
components in an aircraft.

1.24 FUNCTIONAL CHECKS

After a component change a functional test should be carried
out. No matter how simple the changing procedure, or how
carefully it is carried out, and how high the skill of the engineer,
a functional is always carried out unless the maintenance
manual etc. says otherwise. To carry out a functional check we
will discover if the non-return valve in the hydraulic system is
fitted correctly or the flying controls have the correct range of
movement, etc.

Certain systems have built in test circuits to check the
completeness of electronic system/components.

Functional tests do not always verify the quality of
workmanship, the dry soldered joint might not fail initially and
the locking on the turnbuckle may be considered slack, but
functional are still a very important part of verifying serviceability
to laid down standards.

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SECTION 2: TYPES OF ERROR IN MAINTENANCE TASKS

The UK Safety Regulation Group has identified the following as
the TOP TEN Safety Risks currently in Aviation.

 Crew & Human Factors.
 Design Related.
 Regulatory Oversight.
 Company Management.
 Failure to Maintain Safe Separation.
 Freight, Ferry & Positioning Flights.
 Occupant Survivability.
 Incorrect/Inadequate Procedures.
 Non JAA/FAA Operator Safety.
 Failure to Adopt/Fit Best Available Technology.

They are not in order of priority but Crew and Human Factors is
the most significant by a large margin. Crew and Human
Factors can be broken down into six subheadings and again
human factors feature in maintenance, the area with which we
are most concerned.

Crew and Human Factors
 Maintenance Human Factors.
 Omission of Action/Inappropriate Action.
 Flight Handling.
 Poor Professional Judgement/Airmanship.
 Failure in Crew Resource Management.
 Lack of Positional Awareness.

From data analysed by the CAA in 1992, Human Error in
Aircraft Maintenance was due to the following:

 Incorrect installation of components
 Fitting of wrong parts
 Electrical wiring discrepancies
 Loose objects left in aircraft
 Inadequate lubrication
 Access panels/fairings, cowlings not secured
 Fuel/oil caps and fuel panels not secured
 Gear pins not removed before departure

As an illustration of mistakes made by the maintenance
engineer on the shop floor, together with the operational impact
estimated to cost approximately £5m, the following Maintenance
Errors occurred at Britannia Airways:

Maintenance Error Operational Impact
Nose wheel axle washers omitted
during double nose wheel change at
Line Maintenance Base.
Delay; Rework
Brake unit locking bolt omitted during
brake change at Line Base.
Diversion; Delay;
Rework
Aircraft flaps damaged during hangar
‘C’ check.
Rework
Functional check of landing gear not
carried out following maintenance.
Diversion; Delay;
Rework
Leading edge slats damage during
hangar ‘A’ check.
Delay; Ferry flight;
3 sub charters
Engine boroscope plug not replaced
during hangar check.
Rework

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The company found the most common contributory factors for
Human Error in these examples to be as follows:

 Lack of Resource Planning
 Job Distraction
 Lack of Communication
 Inadequate Shift Handover
 Lack of Assertiveness
 Aircraft design
 Perceived Pressure
 Inadequate Maintenance Aids
 Christmas

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SECTION 3: IMPLICATIONS OF ERRORS

From Heinrich’s Ratio of 600 incidents we have 1 fatal accident.
All due to Human Error at any stage of aircraft design,
manufacturer regulation, maintenance, ramp and flight
operations. The cause of an accident results in a huge cost to
the owner/operator and the Insurance Companies.

The insured (RECOVERABLE) costs are for the hull loss,
property damage and personal liability for the passengers and
crew. This will reimburse the company and give compensation
to the relatives of those killed. However, there are costs which
are not recoverable, these include:

 Insurance deductibles
 Insurance premiums
 Loss of use of the aircraft and equipment
 The cost of the accident investigation
 Disruption to the Schedules
 Disruption to Servicing and Maintenance
 The hire and training of new personnel

The above costs are not insurable, but can be calculated in time
and money. It is difficult to measure the loss of the company’s
reputation and future business in money terms. The media
‘latch on to’ companies that have recently had several accidents
which, in turn, affects the public’s keenness to fly with them in
the future.

The loss of reputation and branded image has affected
industries other than aviation. Adverse publicity has affected
Perrier after benzene was found in their water, and Gerald
Ratner the jeweller, after making comments about items sold by
his company.

Of all the means of transport, people are inherently nervous of
flying and are very reliant on a safe image.

Accidents and incidents with their subsequent investigations
can badly affect the morale of the company’s workforce. This is
true if there is a culture of blame, rather than find out why the
person failed, within the company concerned. The uninsured
costs could well exceed the insured costs!

Following several crashes in the late 1970’s of DC10 aircraft,
passengers would often telephone the airlines to find out the
type of aircraft they would be flying on and if it was a DC10,
they would frequently choose to fly with a different airline
operating aircraft other than the DC10.

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SECTION 4: AVOIDING AND MANAGIN G ERRORS

Whilst the aircraft maintenance engineering industry should
always strive towards ensuring that errors do not occur in the
first place, it will never be possible to eradicate them totally.
Therefore all maintenance organizations should aim to ‘manage’
errors. There is nothing new about trying to manage error. All
responsible organizations involved in hazardous operations
have long employed a wide variety of error management (EM)
measures. In maintenance organizations, these include:

 Selection
 training and retraining
 work planning
 job cards
 tags and reminders
 shift handover procedures
 licence-to-work systems
 human resource management
 licensing and certification
 checking and sign-offs
 technical and quality audits
 procedures, manuals, rules and regulations
 disciplinary procedures
 Total Quality Management

These techniques have evolved over many decades. Though
some are tried and tested, they have collectively failed to
prevent a steady rise in maintenance-related errors. Their
limitations include being piecemeal rather than principled,
reactive rather than proactive, and fashion-driven rather than
theory-driven. They also ignore the substantial developments
that have occurred over the last 20 years in understanding the
nature and varieties of human error.

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This brief discussion sets out the fundamental principles of error
management. The aim is to provide a concise summary of the
error management philosophy. Some readers with very practical
turn of mind may shy away from the term 'philosophy’. But all
management depends essentially upon what Earl Wiener has
termed the 'Four P's': philosophy, policy, procedures and
practices. In the case of error management, philosophy is worth
at least double the value of each of the other three. Without a
unifying set of guiding principles, our efforts will have but a
small chance of success.

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4.1 THE PRINCIPLES OF ERROR MANAGEMENT

 Human Error is both universal and inevitable

Human error is not a moral issue. The consequences of
errors may be undesirable, even destructive, but making
them is as much a part of human life as breathing and
sleeping. We include here violations, which are rarely
malicious acts and are often well intentioned. Human
fallibility can be moderated, but it can never be
eliminated. Nor should it be.
 Errors are, not Intrinsically Bad

Success and failure spring from the same psychological
roots. Errors are fundamentally useful and adaptive
things. We are error-guided creatures. Errors mark the
boundaries of the path towards successful action just as
landing lights define the edges of a runway. Without
them, we could neither learn nor acquire the skills that
are essential to safe and efficient work.
 You cannot Change the Human Condition, but you can
Change the Conditions in which Humans Work

The problem with errors is not the psychological
processes that shape them, but the man-made and
sometimes unforgiving workplaces that exist within
complex systems. There are two parts to an error: a
mental state and a situation. States of mind like
moments of inattention or occasional forgetfulness are
givens, but situations are not. And situations vary
enormously in their capacity for provoking unwanted
actions. Identifying these error traps and recognizing
their characteristics are essential preliminaries to
effective error management.

 The Best People can make, the Worst Mistakes

A common belief is that a few inept individuals are
responsible for most of the errors. If this were the case,
the solution to the error problem would be relatively
simple: identify these people and then retrain them, sack
them or promote them out of harm's way. But the record
suggests that the reality is quite different. Some of the
world's worst maintenance-related accidents have been
due to errors committed by highly experienced people
with 30-year blameless records. Errors can strike
anywhere at any time. No one is immune. And it is also
the case that the best people often occupy the most
responsible positions so that their errors can have the
greatest impact upon the system at large.

 People cannot easily avoid those Actions they did not
intend to commit

Blaming people for their errors is emotionally satisfying
but remedially useless. Moral judgments are only
appropriate when the actions go as intended and the
intention is reprehensible. Blame and punishment make
no sense at all when the intention is a good one, but the
actions do not go as planned. We, should not, however,
confuse the issues of blame and accountability.
Everyone ought to be accountable for his or her errors.
If the error maker does not acknowledge the error and
strive to avoid its recurrence, then no lesson has been
learned and little or nothing gained from the experience.

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 Errors are Consequences rather than Causes

The natural human tendency after a bad event is to track
back in time to the first deviant human action and call it
the cause. We then go on to say that Person X caused
the event and punish him or her accordingly - often in
proportion to the extent of the damage or injury. This
may be appropriate in societies that operate by the 'eye
for an eye' principle, but it is totally out of place in
maintenance organizations in which accidents arise from
the complex interaction of many different factors and
where the primary aim of any subsequent inquiry should
be to strengthen the system's defences. From this
perspective, errors are best regarded as consequences
rather than causes. Just like the bad event, errors have
a history.

Each is the product of a chain of events that involves
people, teams, tasks, workplaces and organizations.
Discovering an error is the beginning of the search for
causes not the end. Only by understanding the
circumstances that give rise to them can we hope to limit
the chances of their recurrence.

 Many Errors Fall into Recurrent Patterns

Errors can arise from either a unique combination of
circumstances, or from work situations that recur many
times in the course of maintenance-related activities.
The former are random errors-in the sense that their
occurrence is very hard to foresee - while the latter are
systematic or recurrent errors. As we discussed earlier,

more than half of the human factors incidents in
maintenance are recognized as having occurred before,
often many times. We also observed that certain aspects
of maintenance, particularly reassembly or
reinstallations, commonly give rise to particular kinds of
errors, notably omissions-leaving out essential steps in a
sequence or failing to remove unwanted objects on
completion. Another frequent group of errors involves
miscommunication or lack of communication both within
and between maintenance teams or shifts. Targeting
these recurrent error types is the most effective way of
deploying limited EM resources.

 Safety-significant Errors can occur at all Levels of the
System

Making errors is not the monopoly of those who get their
hands dirty. Managers often think that error reduction
and error containment is something that applies
exclusively to the workforce, the people at the 'sharp
end'. A general rule of thumb, however, is that the higher
up the organization an individual is, the more dangerous
are his or her errors. Error management techniques
need to be applied across the whole system.

 Error Management is about Managing the Manageable

One of the commonest errors in error management is
striving to control the uncontrollable. Most obviously, this
entails trying to change those aspects of human nature
that are virtually unchangeable - that is, our proneness
to distraction, preoccupation, moments of inattention and
occasional forgetting.

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And, when these attempts fail (as they surely will), the
next mistake is to try to shift blame and responsibility
away from the company at large and on to those
unfortunates known to have made errors. It is the
prevalence of these misguided approaches that has led,
in large part, to the steady increase in public awareness
of maintenance - related errors.

Situations, and even systems, are manageable; human
nature - in its broadest sense - is not. Most of the
enduring solutions to human factors problems involve
technical, procedural and organizational measures
rather than purely psychological ones. The problem is
that blaming individuals rather than reforming systems
has its roots deep in human nature. Such a response
may offer some short-term emotional satisfaction, but it
provides little or nothing in the way of improvements. An
important step in effective error management is to
recognize the existence of this fundamental attribution
error psychologists call this person-blaming tendency)
and to fight against it.

 Error management is about Making Good People
Excellent

The assumption is often made that error management is
a process for making a few error-prone people better.
This is not the case. The principal aim of EM to is to
make well trained and highly motivated excellent.
Excellence in any professional activity has two crucial
elements: technical skills and mental skills. Both need to
be acquired through training and practice.

Several studies have shown the mental element is at
least as important as the possession of requisite
technical skills. The mental element involves a number
of different components. Among the most important of
these is mental readiness. Excellent performers
routinely prepare themselves for potentially challenging
activities by mentally rehearsing their responses to a
variety of imagined situations. To do this effectively
requires an understanding of the ways in which a task
can go wrong. In the case of maintenance-related tasks,
this means having an awareness of the varieties of
human error and the situations that provoke them. Self-
knowledge of this kind is at least as important as
anticipating the ways in which a piece of equipment can
fail.

Maintenance staff needs to be trained in two ways. First,
they need to be informed about the ways in which
human performance problems can arise and to be aware
of their recurrent patterns. In other words, they need to
be familiar with the fundamentals of human performance
and the verities of error. Second, they must acquire the
skill of mental preparedness. That is, they should be
trained to approach each task by mentally rehearsing
the ways in which they and their colleagues could go
wrong. This not only alerts them to risks of error-
provoking situations, but also allows them to plan how
they might detect and recover these errors before they
cause harm. Improving the skills of error detection is at
least as important as making people aware of how errors
arise in the first place.

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 There is no One Best Way

This principle applies in two ways. First, there is no one
best technique for error management. Different types of
human factors problems occur at different levels of the
organization and require different management
techniques. Mistakes and violations, for example, have
different underlying mechanisms. Mistakes are mainly
information processing problems, while violations have a
large social and motivational component. Effective or
comprehensive error management involves targeting
different counter-measures at different parts of the
company: the person, the team, the task, the workplace
and the organization as a whole.

Second, there is no one best package of F.M measures.
Different organizational re the 'mixing and matching’ of
different combinations of techniques. Methods that work
well in one company can fail in another, and conversely.
This is why these principles are so important. There are
many ways of achieving principled reduction and
containment of human factors problem is up to each
organization to choose or to develop the methods, work
best for them. It is often better to devise own methods,
or at least to adapt existing techniques to suit local
needs. People are often more likely 'buy in' to home-
grown measures than to ones that have been imported
from elsewhere. So long as the basic principles are
understood and followed, there are many different ways
of achieving effective EM-and most of them have yet to
be devised.

 Effective EM aims at Continuous Reform rather than
Local Fixes

There is always a strong temptation to focus upon the
last few incidents and to try to make sure that they, at
least, will not happen again. This tendency is further
strengthened by the engineer's natural inclination to
solve specific concrete problems. But trying to prevent
the recurrence of individual errors is like swatting
mosquitoes. You kill one and the rest keep coming to
bite you. As pointed out earlier, the only way to solve
the mosquito problem is to drain the swamps in which
they breed. In the case of maintenance errors, this
means reforming the condition under which people work
as well as strengthening and extending the system's
defences. Reform of the system as a whole must be a
continuous process whose aim is to reduce and contain
whole groups of errors rather than single blunders.

 The Management of Error Management

EM has three components: error reduction, error
containment and managing these activities so that they
continue to work effectively. Of these three, the latter is
by far the most challenging and difficult task. For EM to
have a lasting effect, it needs to be continuously
monitored and adjusted to changing conditions. It is
simply not possible to order in a package of EM
measures, implement them and then expect them to
work without any further attention. You cannot just put
them in place and then tick them off as another job
completed. Here, the bulk of the effort lies in the process
rather than the product. In an important sense, the
process - the continuous striving toward system reform -
is the product.

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4.2 SUMMARIZING THE EM P RINCIPLES

 Human error is both universal and inevitable-

 Errors are not intrinsically bad.

 You cannot change the human condition, but you can
change the conditions in which humans work.

 The best people can make the worst mistakes.

 People cannot easily avoid those actions they did not
intend to commit.

 Errors are consequences rather than causes.

 Many errors fall into recurrent patterns.

 Safety-significant errors can occur at all levels of the
system.

 Error management is about managing the
manageable.

 Error management is about making good people
excellent.

 There is no one best way.

 Effective error management aims at continuous reform
rather than local fixes.

 Managing error management is the most challenging
and difficult part of the EM process.

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Human Factors
Chapter 9
HAZARDS IN THE WORKPLACE

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Contents

SECTION 1: HAZARDS IN THE WORKPLACE ------------------------------ 1
1.1 DEALING WITH EMERGENCIES ------------------------------------------ 1
1.2 THE BASIC ACTIONS IN AN EMERGENCY ARE TO: ------------------ 1
CASE 1 ----------------------------------------------------------------------------- 2
CASE 2 ----------------------------------------------------------------------------- 3
CASE 3 ----------------------------------------------------------------------------- 4
CASE 4 ----------------------------------------------------------------------------- 5

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SECTION 1: HAZARDS IN THE WORKP LACE

Hazards in the workplace tend to be a health and safety issue,
relating to the protection of individuals at work. All workplaces
have hazards and aircraft maintenance engineering is no
exception. Health and safety is somewhat separate from human
factors and this chapter therefore gives only a very brief
overview of the issues relating the aircraft maintenance
engineering.

1.1 DEALING WITH EMERGEN CIES

Careful handling of health and safety in the maintenance
environment should serve to minimize risks. However, should
health and safety problems occur, all personnel should know as
far as reasonably practical how to deal with emergency
situations. Emergencies may include:

 An injury to oneself or to a colleague
 A situation that is inherently dangerous, which has the
potential to cause injury (such as the escape of a
noxious substance, or a fire)

Appropriate guidance and training should be provided by the
maintenance organization. The organization should also provide
procedures and facilities for dealing with emergency situations
and these must be adequately communicated to all personnel.
Maintenance organizations should appoint and train one or
more first aiders.

Emergency drills are of great value in potentially dangerous
environments. Aircraft maintenance engineers should take part
in these wherever possible. Knowledge of what to do in an
emergency can save lives.

1.2 THE BASIC ACTIONS IN AN EMERGENCY ARE TO:

 Stay calm and assess the situation

 Observe what has happened

 Look for dangers to oneself and others

 Never put oneself at risk

 Make the area safe

 Protect any casualties from further danger

 Remove the danger if it is safe to do so (i.e. switching off
an electrical current if an electrocution has occurred)

 Be aware of one’s own limitations (e.g. do not fight a fire
unless it is practical to do so)

 Assess all casualties to the best of one’s abilities
(especially if one is a qualified first aider)

 Call for help

 Summon help from those nearby if it is safe for them to
become involved

 Call for local emergency equipment (e.g. fire
extinguisher)

 Call emergency services (ambulance or fire brigade, etc)

 Provide assistance as far as one feels competent to.

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CASE 1

PATIENT DIED PROBABLY DUE LACK OF OXYGEN
SUPPLY

BACKGROUND

As requested for a supply of medical Oxygen, a bottle was
installed in the aircraft for the use of a meda case. The oxygen
requirement was a continuous flow rate of 2 liters per minute.
As per the certifying staff oxygen bottle was checked and found
satisfactory.

Prior to flight once the passenger was in the aircraft the Doctor
checked the oxygen bottle and found in satisfactory condition.
Once the patient was connected to the oxygen bottle installed in
the aircraft, it was noticed that bottle was leaking around its
connection to the regulator and it was noted that pressure has
decreased from 2200 to 1500 psi. A little while later as per the
flight crew the leak had stopped. The oxygen bottle brought
from the hospital was also carried on board.

As per the doctor the hospital oxygen bottle had enough oxygen
to cover the entire flight. The patient was connected to the
hospital oxygen bottle. However no one had checked the bottle
pressure and it was unknown how much oxygen was left in the
bottle.

During approach landing phase 30-35 miles short of the airport,
the doctor had informed that both oxygen bottles were
consumed and no oxygen was available to the patient. Upon
arrival, oxygen was supplied and patient was rushed to the
hospital. It was learned that patient died before reaching the
hospital.

Upon arrival it was noted that oxygen flow of the aircraft
installed bottle was set to max (fully open, 10 liter per minute)
and the regulator connection was extremely tight.

ANALYSIS

Reason for the bottle leak could not be established although it
should have been declared unserviceable once found leaking.
Crew did not check the hospital oxygen bottle and relied on the
information provided by the doctor.

Oxygen bottles were serviced and supplied by a third party.
Poor handling by a person who is not conversant with the
operation led to leak and wrong setting of the regulator.

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CASE 2

AIRCRAFT WAS ABOUT TO MOVE WITH AIRCRAFT
HANDLER AT CLOSE PROXIMITY

BACKGROUND

Aircraft handler had difficulties removing the front chock on
nose wheel. After hitting the front chock, several times, the
chock moved aside about 450 and at that time aircraft handler
noticed that the aircraft wheel moving forward so he left with aft
chock and trolley, and showed the Captain that the chock was
not cleared. No one was injured in this incident.

EVENT INFORMATION

Pilot in charge has noticed during walk-around that nose wheel
was slightly off centre. Emergency brake was “OFF” and was
selected to “PARK” before start of checks. Flight crew was in a
hurry to obtain ATC clearance as one aircraft was back tracking
and other was also ready for departure. Mechanic on duty had
informed verbally that chocks have been removed and he was
disconnecting the headset. Un-feathering of propellers and this
happened to be at the same time that the aircraft handler was
trying to remove chocks. Since crew did not notice that the
chocks were not removed, selected the nose wheel steering.
The centering of the nose wheel kicked the chock forward and
the aircraft jerked. The mechanic rushed to the aircraft and
removed the chocks. First Officer alerted that a person was
close to aircraft, so propeller setting was changed to “START
FEATHER”. The aircraft did not physically moved forward.

194. HUMAN FACTORS
Chapter 9 – Hazards in The Workplace
ISO 9001:2008 Certified For Training Purpose Only
PTC/CM/Human Factors/01 Rev. 00
9 - 4 Mar 2014
PIA Training Centre (PTC)

CASE 3

IN A LAYOVER FLIGHT AT A LINE STATION A CLEANER
WAS LOCKED INSIDE THE AIRCRAFT NEARLY ONE HOUR.

BACKGROUND

This incident occurred on a Friday close to prayer time. There
was two engineering staff on board to carry out some
maintenance work in the afternoon before departure. An elderly
employee working as laborer was doing cabin cleaning.

The flight landed close to noon and after disembarking the
passengers flight crew completed their routine checklists. The
cabin crew reported cabin clear and did the security checks to
confirm that nothing is left by the passengers. One crew
member noticed the cleaner getting in to aircraft at this time as
usual. Since it was the day shutdown at the station, they packed
their belongings and left the aircraft not confirming whether the
cabin cleaning was completed. The ramp staff was outside near
the air stair door and one of them, as requested by the
mechanic, went to collect the tool box which was loaded in the
baggage compartment. As the flight crew came out of the
aircraft, saw the mechanic installing the propeller guards.
Assuming they handed over the aircraft to the mechanic and the
engineer, crew started move away from the aircraft. The flight
attendants reminded the captain, of the door being left open.
When the captain was going to close it, the mechanic climbed
down the steps and closed the door together with the ramp
staff. He again opened the door and got his bag which was left
in the overhead compartment of raw 1. The cleaner at this time
was cleaning the last row seats. Since all the others are outside
and waiting for him, the mechanic hurried to join them, close the
door and left together with the rest of the crew.

None of them including ramp staff realized the cleaner was
inside. The cleaner was left alone inside the aircraft for about
one hour and the airport supervisor called the station assistant
informing that cleaner was left inside the aircraft. He rushed to
open the door to let the cleaner out after obtaining permission
from captain.

195. HUMAN FACTORS
Chapter 9 – Hazards in The Workplace
ISO 9001:2008 Certified For Training Purpose Only
PTC/CM/Human Factors/01 Rev. 00
9 - 5 Mar 2014
PIA Training Centre (PTC)

CASE 4

ATC SEPARATION BREAKDOWN BACKGROUND

Island aviation aircraft departed and mistakenly followed wrong
instrument departure causing separation breakdown with
another aircraft inbound for landing.

Aircraft was taxing out and lining up on runway for departure
with a delay. When they were on the turn to line up and about to
report ready for departure, the controller asked to follow new
instructions. Since it was a new clearance, immediately the co-
pilot took out the chart which has mentioned departure and
briefed the captain who was the pilot flying. According to the
crew, the co-pilot briefed runway heading and left turn to
establish. Without knowing what briefed was wrong the aircraft
took off and turned left towards the eastern side of the field. At
this time another aircraft was on descend and on the North East
of the airfield for landing. The controller noticed both aircraft in
same sector and advised the aircraft that they were flying a
wrong departure. The pilots were puzzled and confidently
reported that they were flying the correct departure. It took a
while for the crew to realize they were flying a wrong departure.

The controller corrected this separation break by giving
necessary instructions and later cleared for correct route.