Module 09

HUMAN FACTORS

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 Module 09 – Human
Factor

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 Module 09 – Human
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Table of
contents

1. General
2. Human Performance and limitations
3. Social Psychology
4. Factors affecting performance
5. Physical environment
6. Tasks
7. Communication
8. Human error
9. Hazards in the workplace

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 Module 09 – Human
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Chapter 09.01
GENERAL

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HF definition

Definition of Human Factors: the Human Factor is the study of

the human behavior in complex technological systems whose aim
is to keep the risk under control.

Human behavior: the human behavior is understood as every

action a person does. This is not only related to the fulfilment of
a task but also to the act of speak, too.

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HF definition

To understand what determines and conditions our behavior, we

need
to understand many sciences:

● Psychology studies the cognitive process (such as attention,

perception, memory, decision taking, etc.) and emotions.
● Physiology and Medicine study the function of the human body.
● Ergonomics, Anthropometry, and Biomechanics contribute to
the optimization of the relation between man and his complex
working environment. They are useful in designing instruments
and displays, according to human characteristics.
● Engineering studies the way to make communications systems
and
software programs easily accessible by the workers.
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SHELL model
SHELL model is an organisation scheme to explain the aircraft
accidents/incidents.

The SHELL model is an acronym, whose letters are the capital

letters of each subject area:

L: Liveware, standing for the man.

S: Software, standing for procedures and rules. (wrong
interpretation of the procedures, badly written handbooks).
H: Hardware, standing for aircraft and instruments (inadequate
equipment, insufficient instruments).
E: Environment, standing for environment, both physical and
organizational one (too noise, fumes, poor safety culture,
company profit).
L: Liveware, standing for people around us, such as colleagues
(communication, supporting manager).

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SHELL
model

The Shell model is

represented by a
with L (Liveware cross
middle )representing
, in
the
, man. its

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SHELL
model
Problems between different elements:

L-H: insufficient instruments, inadequate equipment, unsuitable designing

of the workbenches, hardly accessible working areas;

L-E: not very comfortable places of work, too loud noises, insufficient
lightning, fumes, extreme temperatures, etc;

L-L: the faults of communication between colleagues, or during the shift

change, insufficient staff, lack of supervision, lack of supporting
managers,etc;

L-S: a wrong interpretation of the procedures, badly written handbooks,

badly constructed check list, misunderstanding of the software.

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HF evolution

The first studies on the Human factor started in 1910 (in England).

During World War I the aircraft became more and more

eleborated. There is the problem about staff training. During
World War II the study on Human factor was strengthened, the
focus moved to the psychological aspects in order to solve some
of the operating problems.

In 1977, in Tenerife, a catastrophic accident shocked the world of

aviation, which involves two Boeing, one of the Pan Am and the
other of the KLM.

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HF evolution

After 1977, KLM started first seminars on resources management

in the
cockpit, called CRM (Crew Resources Management).
The aim was to understand the behavior of the crew in order to
prevent from errors and accidents. CMR was very important, but
it contained a basic error: assuming that only pilots were
responsible for the safety.

In the Nineties the study of the human factor started getting in the
world of maintenance thanks to the MRM courses (Maintenance
Resources Management). They stand to maintenance as CRM
courses stand to pilots.

In 2003 the human factor training has been made compulsory by

the European regulations.
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Accidents and incidents
quote

About 70% of all the accidents and the mishaps are due to
human errors, made in one part of the process. They may be
errors made by pilots, by air-traffic controllers, by maintenance
technicians, by planner engineer, by ramp men, etc.

Technology is essential to safety but it wasn’t able to reduce the

percentage of accidents caused by the human errors.

The maintenance error plays a role of about 12%-15% European

sources point out that 15%, in 70% of the accidents due to human
factor, are due to maintenance errors.

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Murphy law

Each accident is caused by multiple causes. The accidents are

caused by many little errors and events. They cause catastrophic
effects when they link up together.

Each reported accident was foreseeable and it could have been

avoided if the chain of the events had been broken The
maintenance error is one of the rings of the chain.

A quote from Murphy law: If something can happen, sooner or

later it will happen.
Murphy Law reminds us that if something is possible, it is
possible it
happens just in those situations and just to us.

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Chapter 09.02
HUMAN PERFORMANCE AND
LIMITATIONS

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Information
processing

The term information processing describes the way our brain

analyzes the information, gives it the right meaning, remembers it
and acts in consequence.

We can compare our mental system to a computer system.

For a human being the information processing consists of

reception phase, through our sense-organs such as the eye and
the ear, of a data transmission system, represented by nerves, of
a data processor represented by our brain.

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Information
processing

Processing information
is a very complex and
articulate process and it
requires the use of
simplified schematic
models.

The brain needs to

understand the meaning
of the received
information but it has
not necessarily to
memorize it.

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Mental model

The outcome of the information process is a mental model of

reality. With the aim of safety, the mental model must essentially
be as true as possible to the operating reality.

This does not depend only on the information coming from our
sense organs, but it depends also on the way they are interpreted.

Some psychological factors, not only related to stress, as it

apparently appears, can also influence the process. It is in
general easier to adapt the world and what we are living to our
mental model, instead of bringing it somehow into question.

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Situation
Awareness

The term situation awareness is related to the operator awareness about

the whole operational situation in relation to its possible and probable
developments.

The degree of professional experience tends also to influence the kind of

error that can be done in case of loss of Situation Awareness.

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Decision
making

The expression decision

making means the
process more or less
conscious, through
which we consider our
available information
and we decide to
undertake an action,
instead of another, or
decide not to act.

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Vision

The eye is a sphere, with a part in direct touch with the outer
world. The
eye has got a natural contact lens, called cornea, in charge of
focusing.

The light gets through the cornea and gets into the pupil that is a
hole in the middle of the eye. According to the strength of the
light the pupil changes its dimension. This enables an adjustment
of the quantity of light that actually can get into the eye.

Then the light passes through a lens, called crystalline, behind

the pupil. The crystalline is a system that enables focusing,
working as a lens that changes its curvature, according to the
change of distance of the objects. The crystalline, changing its
curvature, permits the image to fall down on the retina.
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Vision

In the eye backside there is the retina, which is the film where the
image imprints. Retina consists of light-sensitive cells, called
photoreceptors.

There are two kinds of photoreceptors, cones and rods.

The cones are in charge of colors identification, of the minutely
vision and of the photonic vision since they are stimulated by the
light.
The rods enable night vision, in condition of insufficient
brightness. The rods are also in charge of peripheral vision “tail of
eye”.

They have different reaction time: the rods have longer reaction
time (until 30 minutes). The cones have a short reaction time
(until 7 minutes).
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Vision

Concerning maintenance activities, you need to pay attention

when you do a task in dark environments, as during the analysis
with a contrast medium.

Before undertaking a visual inspection, you need to enter the

darker room and let your eyes get accustomed Generally when
you get into the dark environment you need to wait for your eyes
adaptation.

You do not have to stare at the objects because in this case the
image falls on the fovea where there are not rods.

So you need to move your eyes, making a scanning, to let the

image fall on the rods in order to be recognized.
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Hearing

The ear is the organ of the sense of hearing, which fulfils two
different functions: it is in charge of detecting sounds and it plays
a major role in the sense of balance.

Sounds are conveyed to the brain that is in charge to interpret the

received signals. This process gives a meaning to the sound
message.

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Hearing

The ear is divided into

three parts: the outer
ear, the middle ear and
the inner ear.

These parts are called in

this way due to their
anatomy and because
the sound information
is carried in different
ways.

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Hearing

Outer ear
It collects the sound waves and transmits it in a mechanical way.
It consists of the pinna, by the ear canal and by the eardrum. The
eardrum is a thin membrane that closes the canal and works as a
drum.
Middle ear
It transmits in a mechanical way. The middle ear is a cavity that
includes three small bones, called incus, malleus and stirrup.
Outer ear
It changes sound waves into chemical and electric impulses.
Then they are sent, through the acoustic nerve, to the cerebral
cortex. The vibration of the stirrup makes the cochlea vibrate. In
this way the fluid inside it begins to move and its movement
makes the cells move.
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Hearing

The noise increases the risk in a working environment because it

can:
● Annoy
● Cause speech interferences
● Cause accidents
● Cause fatigue.

Noise causes difficulty in concentration on tasks, regardless of

the nature of noise, such as steady, sudden or repeated. As time
goes by, noise can get a person so nervous to provoke a
complete loss of concentration.

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Hearing
protection
There is a rule governing worker
exposure to noise, providing for
limits on the intensity of the
noise and on time of exposure.

If the noise is between 85 and

90 decibels, it is necessary the
use of PPE (Personal
Protective Equipment), during
the work activities for at least 8
hours.
Instead, if the noise is more than
115 decibels, hearing damage
is immediate.

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Perception

Perception is, on first approximation, an immediate mechanism

that allows putting together the information. It lets us have a first
awareness of the meaning of the information coming from the
outer world.

Perception is the first step of interpretation of the information.

Perception can be influenced and conditioned by many factors

that can be related to the intrinsic characteristics of the object,
to the attribution of particular meaning, to the state of mental
tiredness, etc.

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Claustrophobia, physical access and fear of
height

Claustrophobia, physical access

So discomfort suffered in some small places 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.

Fear of height
Working at significant heights can also be a problem for some
aircraft maintenance engineers, especially when doing ‘crown’
inspections (top of fuselage, etc.). Some engineers may be so
uncomfortable that they are far more concerned about the
height, and holding on to the access equipment, than they are
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 Module 09 – Human
Factor Attention

We can distinguish among

different kinds of attention,
related to the different ways
we pay attention.

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Attention

Focused Attention (or channel attention): it is the attention we pay

to a small group of information, avoiding to get distracted by
other information. It is also called channel or tunnel attention.

Multi-task Attention: the divided or multi-task attention is the

attention we pay when we do many activities at the same time
and each of them requires a certain degree of specific attention.

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Attention

Selected Attention: selective attention is the one ordinary used.

The brain makes normally a selection among all information
coming from our sense organs, even if its level of attention is
very low this kind of attention does not require a particular
degree of concentration and it doesn’t get you tired.

Sustained Attention: sustained attention is the one you have to

pay for long. In general, you do not always pay a high degree of
concentration. Attention intensity on what you are doing depends
mostly on the orderliness of the activity. The higher is the habit of
carrying out specific activities, the lower is the degree of
attention you pay. On the contrary, the newer is the action,
unknown or dangerous, the higher is the attention you pay.

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Memor
y

Our brain has more or less temporary stockrooms that let us
understand information, them the right meaning and
remember
associate them when necessary.

The brain has 3 kinds of memory:

● The sensory memory
● The short-term memory or working
memory
● The long-term memory.

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Memory

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Memory

Sensory memory: when the information is received by our sense

organs it is kept for a very short time in a first memory (sensory
memory). Sensory memory is in charge of binding information
together, in order to give it a first meaning.

Short term memory: the Short Term Memory (STM) or better told
working memory, is a memory that works on information, putting
them and getting them out from the permanent memory. The
STM can keep and rework only a small quantity of Information.

Long-term memory: the Long Term Memory (LTM) is a permanent

storehouse, where all information collected during a lifetime are
stored. The information written in the long-term memory is
permanent.

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Memor
y
The long-term memory can be divided into declarative (explicit) and
procedural
(implicit) memory.

The declarative memory can be further divided in episodic and semantic.

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Chapter 09.03
SOCIAL
PSYCHOLOGY

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Responsibilit
y

Individual Responsibility: the main advantage of individual

responsibility is that an engineer/technician understands clearly
tasks assigned to him and it is his job to do them. 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.

Group Responsibility: the advantages of group responsibility 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.
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
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Motivation

Motivation is a determinant
factor for the effectiveness
of the professional
performance and for this
reason it must be highly
considered. It represents
the difference between
what an individual is able
to do and what he will do.
According to the position in
the pyramid of needs,
human behavior is
motivated.

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Safety culture

The culture of an organization represents the leading structure of

the organization. Different cultures should not contrast one
another and it is essential to put always safety subjects at first.

The culture of safety must have the following characteristics:

● The culture of safety is the engine that constantly drives the
organization to achieve an outright security.
● The culture of safety does not forget the risk and reminds
organization members that human beings can make errors.
● It creates an atmosphere of confidence, where people are
encouraged to give information about safety.
● It is a culture that clearly expresses the demarcation line
between acceptable and unacceptable behaviors.

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Team work

The term working group is used to describe a group of people who

interact with a common aim.

In order to be a successful group it is essential to divide up duties

and responsibilities. In other words each person must know what
his/her task is. The presence of a superintendent in charge to
lead and to manage the group is also required.

A maintenance working group can be composed of:

● A team of technicians, working on a specific task, on board of
the
same aircraft
● A group working on the same shift
● A group working in the same location.
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Team work

Conformism: the term conformism is referred to the tendency of

the single person to conform to what he imagines the others
expect from him. This characteristic is positive because it lets
the individual fit into the group he joins. But it will can be also
very dangerous.

Peer pressure: the term peer pressure is used to describe the

tendency of colleagues to make the others conform to a certain
kind of behavior or to the group opinions. This tendency may be
expressed in different forms, like hurrying someone to speed up
activities, pushing others to conform to habits in contrast with
safety, such as taking shortcuts during routine activities and not
to consult the handbook, sometimes using irreverent sentences
like: “Do you really believe to consult the handbook for such a
simple task? Please...”
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Team work

Polarization: the polarization is the group tendency to take the

most extreme decisions regardless of the single individual ones.
This is what in everyday language is said: “there is strength in
numbers”, which means that, if in a group you find ideas
corresponding to yours own, you feel supported. By influencing
one another, you can bring the group towards stronger choices
and in some cases extremes.

Social laziness: the social laziness is the tendency to devolve

tasks to the other members of the group. This tendency becomes
extreme if there isn’t a clear subdivision of duties and tasks. The
social laziness has been studied in the behavior of crews.

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Relational
skills

To work successfully in a
group, it is necessary to
know rules, but this is not
enough. It is also
necessary to develop
relational abilities and to
address to other people in
a positive way.
Main relational skills
expressed by a successful
group are: communication,
cooperation, coordination
and mutual support.

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Relational
skills

Communication: in a group you are required to communicate

efficiently. Above all the essential thing is an effective
communication of information about safety. A good
communication helps the group integration and it creates a good
working mood.

Cooperation: it is the ability “to work in team”, to keep together a

well- mixed group, to create positive spirit of cooperation and to
respect the others. It is mainly up to the leader to succeed in
keeping the group together letting the cooperation among people
be easy.

Coordination: it refers to the subdivision of roles, of duties and

responsibilities in order to accomplish the tasks. This area
includes the general organization, the distribution of individual
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Managemen
t

So, a successful group

needs clear subdivisions
of tasks and roles, as
well as a person in
charge to lead the group
and to verify that
everyone carries out his
task in an adequate way.

In big companies there

are different
professional figures,
having the role of
leading people, at
different levels of the
hierarchic ladder.
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Management

Operating Manager: he manages people working on the field

(technicians).

Intermediate Manager: he is in charge of managing and

coordinating people managing the technicians.

Strategic Manager: he is on the top of he organization and carries

out a strategic management.

In operational reality it isn’t possible to apply an ideal safety. It is

most common to find a good compromize betweeen commercial
principals and safety principle.

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Team leader

The term leader means a person who can influence and lead the
behavior of the group, who generally is in the uppermost position
in the company.

Organizations chose people who are officially nominated as

leader, more specified as superintendent, chief group, supervisor,
manager, etc.
This formal assignment should correspond to the person
recognized as leader by the group. But unfortunately it is not
always so. The leader chosen by the company, also called formal
leader, does not always correspond to the informal leader, the
one chosen by the group.

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Team leader

Styles of leadership (team leader):

● Autocratic leader: he imposes his decisions he doesn’t ask
for the
opinion of the others
● Democratic leader: team behaviors are part of the decision-
making process and are involved in the project and that
support the leader in ensuring that the objectives of each
individual coincide with those of the company this
approach motivates the whole team and makes the job more
complex but also more engaging
Style of delegation: the team knows how to act and what to do
and leaves to the leader the sole responsibility of taking
decisions.

A true leader will have to adopt a different style according to the

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 Module 09 – Human
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Chapter 09.04
FACTORS AFFECTING
PERFORMANCE

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 Module 09 – Human
Factor Circadian
rhythms

Another important
aspect to
physical conside
concerning r
performances is huma the
metabolism of n
our which is not
alwaysbody,
the
same but it changes in a
day.

More precisely they

change during the 24
day hours. These
rhythms are called
CIRCADIAN RHYTHMS.

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Circadian
rhythms

Circadian rhythms are

controlled by some deep
parts of our brain placed
in that area called
limbic system.

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Circadian
rhythms

Morning type people

There are some people who prefer carry out the main part of their
activities during the morning because there they feel more active
and have stronger mental and physical energy. This type of
people is called MORNING TYPE: they have circadian rhythms
anticipated with main activation during the first part of the day.

Evening type people

There are some people struggling to activate themselves during
the day, while they work really efficiently at the end of the day and
in the evening. They are people with late circadian rhythms. This
typology of people is called EVENINGTYPE.

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Circadian
rhythms

Main circadian rhythms

influencing the activity
of our organism.

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Circadian
rhythms

Body temperature
As for machines the level of temperature shows the work that the
machine is carrying out. When the machine is hot it means that it
is working, when it is cold it means that it is at rest. Also for the
human body, temperature shows the metabolism level or better if
it is working at the top or at the bottom level. Foe example a
decrease in temperature means a decrease of the mental
performance.

Appetite
During the night, when you sleep, stimuli of hunger are inhibited,
because the organism is resting and extra energy received by
eating is not necessary. On the contrary, wakefulness activates
centers provoking sensation of appetite, or hunger in order to put
energy in the organism.
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Stres
s
Actually, in scientific
field, the term stress has
a neutral meaning and
not a negative one. The
term stress relates to
tension
the state of the human
organis is subjected,
m
when it is called to react
to some stimuli.

You usually realize your

state of tension (stress),
when it is very strong and
it starts to have a
negative influence.

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Stres
s

In presence of stress the body always reacts in the same way:

● There is a body tension
● There is a mind tension
● There is an emotional tension.

The organism reaction to the stress implies the activation of the

sympathetic and parasympathetic nervous system.
General Adaptation Syndrome phases are:
● Alarm
● Resistance
● Exhaustion.

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Workload

The term workload is referred to the load of work, or better to the

required engagement of a technician for carrying out of a specific
task.

The engagement can depend on many variables, not easily

measured. They depend on training, on procedures, on
presence of stressors, on the kind of task and required
standard.

Let’s imagine carrying out in two hours three easy and

unimportant tasks. If you decrease time, of one hour or thirty
minutes, or if you increase the importance, with difficult duties,
the workload will increase consequently. A particular stressor is
represented by time pressure. One consequence can be push
technicians taking procedural shortcut, risking this way to
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Workload

There are then different levels of workload varying from very light
to
very hard workload:
● Overload
● High load
● Normal workload
● Underload or insufficient workload.

Underload: this situation creates a very low level of mental

activation.
Normal workload: the effort required is optimal.
High load: the work is carried out under pressure.
Overload: it is impossible to fulfill the task requirements.

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Sleep

Sleep is divided in two stages:

● The first part of the sleep is called NOT REM (NREM) sleep,
called also orthodox sleep, because both mind and body are in
a condition of rest.
● Later sleep changes becoming REM sleep, or paradoxical
sleep, because the body is deeply relaxed while the brain has
an activity similar to wakefulness. This stage is called REM that
is the abbreviation for Rapid Eyes Movement, for the typical
movement of the eyes that is its main characteristics.

When we wake up our brain needs a certain period of time to be

completely active. This period of transition between sleep and
complete wakefulness is called sleep inertia. Concerning safety,
it’s better to pay attention to it.

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Sleep:
NREM

The NREM sleep is

divided in four stages,
because in each one of
them the electric waves
produced by brain have
a different trend.

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Sleep:
REM

The REM sleep lasts

some minutes (2-10
minutes). It recurs
several times during the
night you get near the
awakening.

The REM and NREM

phases alternate
After some hours of
sleep the brain doesn’t
pass through phases 3-4.

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Shift

In aviation world the maintenance activity is carried out on 24

hours of
a day.
For this reason it is normal for maintenance technicians to work
also on night shifts.

Night shifts are very dangerous for safety because at night the
quality of physical, but especially of mental performance
decreases.
The investigations on aircraft accidents, whose cause is to be
found in an error in maintenance activities, have revealed that
most of these activities have been carried out during a nightshift.

For this reason it is necessary to make an optimal schedule of

night shifts.
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Shift

Shifts can be divided in 8 hours or 12 hours shifts. The most

common shift is 8 hours one. The shifts turnover is divided in fixed,
weekly and alternating and follows general rules.

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Shift

Fixed work
● Circadian rhythms keep the diurnal trend during the first 3 days
of
night shift
● They start changing during the fourth night but the
adjustment is not immediate
● After a maximum of 5 days of work you have at least 2 days
of rest (in these 2 days the organism takes at once its diurnal
trend again).

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Shift

Weekly shift
● Weekly shifts are not optimal After one week, just when the
organism begins getting used, the shift changes again It
makes the rhythms to adjust again
● This shift causes a serious fatigue.

Alternating shift
● Shift type changes every 2 or 3 days
● These are the best shifts over the 5 weekly working days
there are maximum 3 night shifts, one after the other, in order
to give the lowest fatigue of de-synchronization the body
keeps the diurnal rhythm

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Fatigue

From a working point of view we define fatigue as a condition of

tiredness associated to long working hours or sleepless periods,
or to de-synchronized working rhythms, as in night shifts.

It corresponds to a decrease of ability in accomplishing a task, to

deterioration of the work quality, to accuracy and to the decline of
interest and motivation.

There are three types of fatigue:

● Sharp: short but intense
● Chronic: prolonged in time
● Cumulative: results of many periods of fatigue.

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Fatigue

For safety’s sake, it is fundamental learning to recognize

consequences
of fatigue on the performance and to be able to avoid them:
● The level of attention
● The Judgment Ability
● Short Term Memory
● The visual acuity
● Motor faculties
● Relational faculties.

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Fatigue

Countermeasures:
● To follow general rules indicated for sleep health and for
management of fatigue
● When you work on shifts it is necessary that technicians fix the
time for meals and rest
● It is necessary to weigh up the effective possibility of carrying
out night overtime shifts.

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Medicines

Medicines are generally taken to cure some diseases. As general

rule, you have to consider that each medicine even if prescript by
a doctor may have collateral effects.

Antibiotics: this category of medicines doesn’t cause direct

effects on mental performance, they can cause a general
condition of exhaustion. And consequently they can cause
fatigue and concentration difficulty.
Painkillers: these medicines don’t cause alteration of mental
faculties, but if associated to other substances, they can interfere
with the cognitive performance.
Sleeping tablets: they are medicines that, by their nature, alter the
mental performance.

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Alcool and
drugs

Alcohol is a substance that, by its nature, causes alterations to

mental functions. Of course the degree of the alteration depends
on the quantity of alcohol drunk and on the alcoholic % of the
drink.
Regarding safety, on the contrary, alcohol is totally contra-
indicated. In all organizations operating in the safety field,
alcohol distribution in staff restaurants should be forbidden,
especially in aviation field.

Drugs are also substances altering mental functions. They are

absolutely contra-indicated for safety and drug-taking is
forbidden for people working in the aviation field.

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Chapter 09.05
PHYSICAL
ENVIRONMENT

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Noise

Noise is one of the riskiest stimuli in the maintenance

environment.
Noise is defined as an unpleasant and annoying sound, especially
if it is loud. Noise is by nature stressful; namely, it is a stimulus
that forces the organism to a tension and to an adaptation.

If we are concentrating on performing a task while there are

noises around us, the effort is greater, because our brain has to
reject the background noise and place the task in the foreground.
As time passes concentration becomes increasingly difficult and
a sense of mental fatigue arises, which we often realize when the
noise ceases.

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Nois
e

Noise in the workplace can have adverse effects in both the

short and
the long term.

The main effects of noise are:

● Annoyance
● Interference during conversation
● Sleep disturbance
● Momentary reduction of mental efficiency
● Extra-auditory effects.

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Noise
management

The organization i
responsible for putting s
noise systems in
control
place.
There are three levels
for reducing the
exposure of workers to
noise.

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Noise
management

First level - At the source

The noise level is reduced from the source using specific
silencers.
Second level - Between the source and the worker
Insulation: this system consists in using absorbent materials that
can be placed between the noise source and the worker. The
sound waves have to firstly pass through this material before
reaching the worker in reduced form.
Echo absorption: this consists in placing absorbent materials on
the walls, roofs, floors and other surfaces that might reflect the
sound waves.
Third level - At worker level
Protective equipment like headsets and plugs can be provided if
the continuous noise is higher than 87 db.
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Illumination

Inappropriate or insufficient lighting can lead to an increase in

mistakes
in tasks as well as an increase of the time required to complete
them.
With a better illumination an increasing of the performance is
possible, speeding up activities and reducing errors.

Lighting means the quantity of light that reaches a surface or an

object. It depends on the light emitted by each light source and
on their aiming. It can be subdivided into:
● Base lighting, i.e. of the structure and of the environment in
general, such as the hangar
● Additional and dedicated lighting, specific for a task, such as
for
instance Non- Destructive Checks (NDCs) or boroscope
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Illumination
problems

Reverberation occurs when the lighting intensity is too high. This

phenomenon can cause a reduction of visual perception,
distortion of colors, fatigue and irritation.

Direct reverberation: the direct reverberation zone is defined as

that area between 0 and 45 degrees in relation to our field of
view line, in which a strong light is received. It therefore occurs
when a light directly strikes our field of view.
Indirect reverberation: it is caused by light reflected on surfaces.
Indirect reverberation is relatively easy to control by coating
reflecting surfaces with matt paint and moving light sources
away from areas that cause reflection.

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Fumes

By nature, aircraft maintenance takes place in an environment with

a
high presence of fumes and emissions.

Fumes are caused by combustion, overheating or emissions from

chemical substances.
The presence of certain fumes is detected by their smell;
conversely, others cannot be detected, as they are practically
odorless.

Fumes represent a problem for the engineer in terms of both

health and performance. They can also cause local irritations
such as irritation of the eyes.

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Temperature

It is important to understand the effects of temperature on the

safety
and performance of works.

Regardless of individual preference, cold stress is more insidious,

as it prevents manual dexterity. Though hot stress is often
perceived as more fastidious, from the point of view of the
maintenance task, hot stress does not significantly interfere with
manual dexterity.

In addition, the sensation of comfort is affected not only by the

temperature but also by the humidity rate. When the humidity
rate exceeds 50%, also the intensity of the degrees perceived
increases.

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Vibration

Vibrations in aeronautical maintenance are caused by the use of

percussion equipment or tools with repetitive movements. Also
low noise frequencies like those caused by an engine can cause
vibrations.

Vibrations ranging between 0.5 Hz and 20 Hz are problematic

because they are absorbed by the human body. Vibrations within
the 50-150 Hz range, such as those caused by pneumatic guns,
cause the white finger syndrome.

The harmfulness of vibrations depends on the characteristics and

the conditions in which they are transmitted: extension of the
contact area with the object that vibrates, the vibration
frequency, the direction of propagation and the exposure time.

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Working environment

Among the further factors of the working environment that affect

performance, we can mention the following:
● Cleanliness and tidiness of the workplace, structures for
storing and keeping the tools used, presence of manuals and
access to information, continuous checking that the used
tools are put back in their special housings to avoid
inconveniences and FOD (Foreign Object Debris)
● Use of adequate safety equipment and non-slip surface
procedures, safety slings
● Use and storage of chemical substances and toxic fluids, clear
differentiation of the containers to avoid confounding the
contents, use of clear labels, storage in separate places of
containers that can be confused, etc.

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Chapter
09.06
TASKS

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Physical and mental
work

Before starting each maintenance task it is necessary to plan what

it
must be carried out. It is advisable to follow some support check
lists.

For example the technician can try to answer the following

questions before starting a task:
● Do I exactly know what the task is about and how it has to be
carried out?
● Are sources, instruments, people, equipment, documentation
and supports available in order to carry out the task in a
successful way?
● Am I sufficiently skilled to accomplish the task?

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Repetitive and routine
tasks

Repetitive tasks are composed by parts of an action that are

always repeated in the same way. Routine tasks instead are often
carried out, every day, or many times in one shift or in one week
(daily checks).

The repetitive and the routine tasks require an average cognitive

effort. In order to carry out these tasks a certain level of mental
elaboration is required. It is necessary to pay a higher attention
than during physical tasks. The ever-similar repetition of the
actions causes a natural fall of attention.

In order to avoid it, it is necessary to follow check lists and

procedures.
When possible, it is necessary to make short breaks in order to
relieve the possible boredom.
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Complacenc
y

The tendency to work

with an excessive self-
confidence, which leads
avoidin the procedure
to
g is called
checks
complacency.

Complacency deals with

the idea of excess of
self- confidence The
complacency put the
safety at risks.

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Visual
inspection

The visual inspection can be described as the process of

examining and assessing the conditions of a system or of a
component, using only the sight, with or without the help of
instruments. It is one of the main and most important methods
used in maintenance to guarantee the airworthiness of an
aircraft.

The main instruments used for a visual inspection are:

● Small mirrors or magnifiers
● Torches or drop-lights
● Borescopes
● Optical fibers
● Camcorders
● Laptops with optical screen.
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Complex
system

All the skills we exert to carry out a work in a complex system

require a very high cognitive effort and a very high level of
processing information. The activity of searching breakdowns is
a classic example. Analysis of the problem, diagnosis, problem
solving, reasoning, decision making are all very high cognitive
skills that are used when carrying out tasks in a complex system.

In order to carry out the maintenance of complex systems it is

necessary for a technician to be specifically trained on the
systems, their composition and their functioning. The training
must provide the right balance between detailed knowledge of
the system and techniques of analysis of the breakdown.

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Chapter 09.07
COMMUNICATIO
N

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Definition

Communication can be defined as a stream of information. This

process gets started by the sender, which can be a human being,
I.E. a technician telling something to a colleague, or something
organized, like a notice from the company put on a board or sent
via internet. The subject getting the information is the receiver.

When the sender communicates with the receiver but has no real
time answer, this is called a one way communication. The
technician reads the note but can’t reply or eventually clarify any
doubt immediately.

When the sender transmits something and the receiver is capable

of a prompt reply we can talk of a two ways communication.
When two technicians are talking, they are giving each other
information and any of them can ask questions and reply.
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Definition

Synchronous communication takes place in real time and it is

commonly used by pilots and flight controllers.
Errors can occur, following Reason model, and they have
immediate consequence on flight operations.

Asynchronous communication does not take place in real time.

This kind of communication is typical of maintenance. Notices,
messages, guidelines, job cards are written and read later on by
technicians. Following Reason model, errors can occur but they
do not have immediate consequence and are therefore latent.
This is especially true for pilots and maintenance technicians

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Functions

Communication has three main functions:

● To give information. Through manuals, notes, reports and job
cards. But also a colleague, a supervisor, an engineer could be
a useful source of additional information.
● To create relationships. Communication is the way to create
relationships and when they are of a good quality this can help
to establish a friendly and cooperative environment,
fundamental for an effective flow of information and for an
exchange of points of view. This guarantees adequate levels
of safety.
● To perform tasks. Communication is the way by which staff
carries out tasks, applying written advices, sharing duties,
sending and receiving information etc.

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Verbal and non verbal

communication

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Errors in
communication

During handover, the errors may occur due to:

● Lack of communication. When a technician forgets to pass
important details or if a message is diverted. This can happen,
for example, when a written message is left in the wrong place
and not seen by the receiver.
● Poor communication. When the technician does not clarify all
his needs receiving then inappropriate information, or else
when a written report is filled in a barely legible handwriting.

Simple rules to be followed in order to avoid poor and inefficient

communication are: speak and write clearly, listen and read
carefully
and ask for explanations any time you feel the need.

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Effective
communication
To perform an effective
written communication
there is a 4 C rule to be
followed:
CLEAR: communication
must be written in a
legible handwriting,
capital letters
CORRECT: it must refer
to manuals and
procedures
COMPLETE: no
information has to be
left out
CONCISE:
communication must
be synthetic, noEd2
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 Module 09 – Human
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Keeping up to
date

An aeronautical technician must constantly update his skills. To

do this
he needs to know:
● New aircraft and certified variants
● New equipment and new maintenance practices
● Changes made to aircraft he’s working on
● Reviewed maintenance procedures.

There are many ways to spread information: hand given

documents, notices on boards, company intranet or Authority or
internet web sites.

When the information is particularly important the company may

require the technician to sign a receipt.
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Chapter 09.08
HUMAN ERROR

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Error definition

Generally, the term error means any action that departs from what
has
been programmed or expected.

Here, by error, we mean an action that departs from an expected

standard and that can jeopardize safety. Generally the error is
unintentional, in the meaning that the person who makes it has
no intention of doing so.

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Error
classification

Over the years, much commitment has been devoted to error

classification in order to understand its nature and the factors
that can help it to arise:
● Design or operator-induced error
● Variable or constant error
● Reversible or irreversible error
● Omission, commission and extraneousness errors
● Slips, Lapses and Mistakes.

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Error
classification

Design or operator-induced errors

● Design errors errors made in design or production
● Operator-induced errors errors made by the operator that
works on the aircraft.

Variable or constant errors

● Variable errors random errors
● Constant errors errors that occur with a certain frequency.

Reversible or irreversible errors

● Reversible errors errors can be corrected
● Irreversible errors errors cannot be connected.

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Error
classification

Omission, commission and extraneous errors

● Omission missing action
● Commission incorrect performance of a task (true and
proper error)
● Extraneous error extraneous action to plans.

Slips, Lapses and Mistakes

● Slip inattention error (little attention)
● Lapses memory errors (momentary and transient)
● Mistakes more complex execution (high degree of attention)

programming and planning errors.

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Violation definition

Violations means conscious deeds that depart from the rule and
which
can involve a safety hazard.

In most cases, persons do not commit violations with the

intention of sabotage.

To the contrary, in some way they assume they are following a

better strategy than the one specified, violating with the purpose
of saving time or to avoid a pointless rule.

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 Module 09 – Human
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Rasmussen
model

One of the most well-

known models which are
helpful for understandin
and classifying
g huma
errors is Rasmussen’s.
n

In any case they do not

think they are
compromising safety.

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 Module 09 – Human
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Rasmussen
model
This model connects errors on the basis of three different levels of
behaviour:

Skill-based. This is the least binding level on the cognitive plane. The
actions accomplished are carried out automatically, without conscious
attention and are the result of a lot of practice.

Rule-based. This level concerns the application of well-known rules or

procedures in familiar situations. Conscious attention is devoted
because people recover rules stored in the memory to apply them.

Knowledge-based. This is a matter of all those new and unknown

situations in which it is necessary to reason to find a solution. These
require a high level of concentration.

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Reason
model

No accident has ever

been caused by only one
person, like for example
an error made by a pilot,
but rather by a long
series of small errors
made in various parts of
the system.

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Reason model

The danger arises when the holes that represent the errors and
problems are lined up with one another. This way, they open the
passage so that a problem generated in more remote parts of the
system reaches front-line operation causing an accident.

James Reason defines this alignment of active and latent errors

as the
accident trajectory.

The errors made by direct operators, such as pilots, air traffic

controllers and partly by engineers are called active failures.
These active errors have an immediate consequence on safety,
as they directly cause a failure, or in more serious cases, a true
and proper accident.

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Reason
model
In the aviation system, errors are made also in other spheres, i.e. sectors
not directly linked with a critical event. These are called latent failures, as
their consequences are delayed in time. It is important to remember that
latent failures are the hardest to detect because they are made in sectors
of the system not directly connected with management of the aircraft.

Errors and problems are inherent in every part of the system: they must be
identified and blocked immediately through “safety barriers” to prevent
them from having consequences. The safety barriers are therefore the
actions carried out to solve the error.

The danger arises when the holes that represent the errors and problems
are lined up with one another. This way, they open the passage so that a
problem generated in more remote parts of the system reaches front-line
operation causing an accident. James Reason defines this alignment of
active and latent errors as the “accident trajectory”.
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Dirty dozen

Mr. Dupont of the Canadian Aviation Authority carried out a

thorough investigation on the major aviation accidents and
incidents, where the cause was due to maintenance errors. The
purpose
certain wasfactors
to identify
present in different accidents. This way he
risk certain risk elements shared by all accidents, whic
characterized
discovered the context in which the error was made. h

He identified twelve of them and brought them together in the

following list, called Dirty Dozen.

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Dirty dozen

Risk factors present in different accidents:

1. Lack of communication: a lack of clear direct statements and good
skills;
2. Self-complacency: self-satisfaction accompanied by a loss of
awareness
of the potential dangers;
3. Lack of knowledge: lack of experience or training in the task at
hand;
4. Distraction: drawing one’s attention away from a task;
5. Lack of teamwork: working together to achieve a common goal;
6. Fatigue: weariness from labor or exertion, nervous exhaustion or
the temporary loss of power to respond;

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Dirty dozen

Risk factors present in different accidents:

7. Lack of resources, in the meaning of both the lack of
instrumentation and lack of personnel, i.e., failure to use or
acquire the appropriate tools, equipment, information and
procedures for the task at hand;
8. Pressure: pushing for something in spite of opposing odds,
creating a sense of urgency or haste;
9. Lack of assertiveness: lack of the capability to communicate
effectively and directly one’s own opinion;
10. Stress: mental, emotional or physical tension, strain or distress;
11. Lack of alertness: failure to be alert or vigilant in observing;
12. Norms: commonly accepted practices where assumptions
are made that the course of action or procedure is
corrected based on history without re-validating or verifying
the current procedure.

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Dirty dozen

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Error
management

Unfortunately, the
objective of never
making a mistake
cannot be achieved,
because man by nature is
likely to err.
The organization must
therefore predict this
possibility as ingrained
in maintenance
activities and be
structured to prevent
errors or prevent them
from having
consequences.
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Error
management

Error reduction
It is the lowering the likelihood of an error being made. It requires
an
upstream intervention before the error made.
Error capture
It is the strategy presumes that the error has already been made.
The objective of intervention is to locate it before the aircraft
flies. Example: double checks.
Error tolerance
It is the capability of the system to absorb the error without it
having effects and therefore of annulling its consequences.
Example: redundancy of the system.

It is also important the OCCURRENCE REPORTING SYSTEM.

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Chapter 09.09
HAZARDS IN THE
WORKPLACE

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Recognising
hazards

Every working place presents potentially hazardous situations and

aircraft maintenance is not an exception. Actually is quite the
opposite.

Physical hazards in workplace:

● Hazards related to the use of machines
● Danger of falling from ladders and ramps
● Electrical hazards
● Risk related to substances used (chemicals, toxic substances)
● Fire hazards
● Continuous physical stress or sudden noises
● Stress due to climate, temperature and humidity
● Stresses of the musculoskeletal system.

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Electric
shock

The effect of electricity

human
on depends on
body physical
individual and on
discharge
conditions
intensity.

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Fire

Maintenance is exposed
to fire or explosion more
than any other working
environment.

This is due to the

presence of
combustions,
unrestrained flames or
flammable substances.

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Fire

Fire can be classified as follows:

● Class A: flames coming from wood, paper, cloth etc. These can
be
extinguished by water or water solutions.
● Class B: flames coming from gasoline, solvents and greases.
These fires can be controlled by dilution, by preventing
ventilation or by suffocation
● Class C: flames involving electrical equipment such as
engines, transformers or switches. These fires can be kept in
control by using non conductive materials. NEVER USE WATER.

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Burns

Objects at high temperature must be safely handled in order to

avoid burns. Very low temperature can also be responsible for
burns, especially when very cold metal surfaces are involved.

Burn severity depends on:

● Length of contact with skin
● Object shape and smoothness
● Pressure in the skin
● Affected area
● Object temperature.

To avoid any burn, protective gloves must be worn when working

in very cold/hot environments.

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 Module 09 – Human
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Emergenc
y

Workers must be aware of

every potential danger in their
working
environmen and must be
t
informe on how to avoid
d if they can’t be
dangers,

removed
This must be done by a
.specific training and by using
tags and signs near the
source of danger.

In general red signs

indicates danger, yellow
signs indicates warnings and
blue signs indicate general
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Emergency

When managing maintenance, a security policy must include

a
declaration by the managing supervisor guaranteeing that:
● Possible risks related to the job have been evaluated
● Procedures for the correct handling of dangerous goods,
system running, facilities and tools usage have been defined
and are ready at hand for any worker
● Every worker has been informed of potential risks in their
working environment
● Training in case of emergency has been done
● Safety procedures and prevention have been done, like use of
special equipment and self protection tools
● A safety supervisor, capable of coordinating prevention and
protection from danger, has been appointed.
01.04.202 Ed2 Pag.12
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Thank you for your
attention.

Pag
.