Human factors in Aviation

HUMAN FACTORS
TRAINING PROGRAM

LEARNING OBJECTIVE
 Examine and explain how the working environment and human
factors affect personnel,
 Show and develop ways to prevent or lessen the seriousness of
these effects.

COURSE CONTENT
HUMAN FACTORS BASICS
REASON’S MODEL & HFACS
SHEL MODEL

WHAT IS/ARE HUMAN FACTORS?
 How does it affect me?
 Why should I care.... Isn’t it just another tool for management to
make my life difficult?

DEFINITION: HUMAN FACTORS
 Human Factors covers a range of issues including the perceptual,
physical and mental capabilities, the interaction and effects on
individuals of their job and working environments, the influence of
equipment and system design on human performance and
finally the organisational characteristics which influence safety
related behavior at work.

DEFINITION: HUMAN FACTORS
Human Factors covers three areas of influence on people at work:
 The organization,
 The job,
 Personal factors.
These three areas are affected by:
 The systems of communication within the organisation,
 The training system and procedures in operation.
All of which are directed at preventing human error and accidents.

BRITISH AIRWAYS FLIGHT 5390
 British Airways BAC1-11, flying from Birmingham to Malaga, Spain.
 Plane climbed to 17,300ft (5,273m), over Didcot in Oxfordshire.
 A loud bang was heard throughout the plane, and the cabin filled with fog
(rapid decompression).
 The cause was that the Captain’s windscreen (L/H Side) had blown off the
airframe.
 Captain was partially “sucked out” of the flight deck, with his upper body
outside of the aircraft.
 Crew assisted in keeping the Captain’s legs inside the flight deck, meaning
the Captain was partially exposed to thin air, 500mph slipstream, low
temperatures and extreme windchill for 22 minutes before the plane landed
at Southampton. The Captain survived the trauma and returned to the
cockpit 5 months later.

FLIGHT 5390 FINDINGS
 The investigating officer found that the wind screen was fitted
from outside the cockpit on this A/C type.
 Some bolts were missing. He took samples of the remaining
installed bolts.
 As per maintenance history, the wind screen was replaced the
previous night, along with new fasteners/bolts securing the unit to
the frame.

FLIGHT 5390 FINDINGS
The investigating officer interviewed the technician. He found the previously
removed bolts in a dustbin. His observations were:
 The technician was very experienced & had “over-confidence”.
 He matched the removed bolts by part number, but did not refer to the IPC,
CMM or AMM for the correct size. 84 of the 90 windscreen retention bolts
were 0.026 inches too small in diameter, while the remaining six were 0.1
inches too short.
 He did not have the proper approach while replacing the windscreen & had
to lean and work in an awkward position.
 He was under pressure to fix the windscreen as the A/C was scheduled for
flight the following morning.
 There was no other engineer/supervisor to verify the work carried out.

FLIGHT 5390 ROOT CAUSE ANALYSIS
As the plane achieves an altitude, there is a difference in atmospheric
pressure between the inside and outside the cockpit and cabin. The
windscreen was fitted and secured from outside the cockpit and thus
had to work against this pressure.
During investigation, it was found that the bolts used were the incorrect
size, and were at least 1 size too small. As differential pressure
increased, the bolts could not hold on & started giving away.
Eventually the wind screen blew out, leading to rapid decompression.
Further investigation found that the removed bolts were also of wrong
size. The technician tried to find a match with removed bolts without
referring to the maintenance data.

FLIGHT 5390 ROOT CAUSE ANALYSIS
The reasons can be categorised as follows:
 Physical factors:
 The wind screen was fitted from outside as per design. Thus has to work against
vacuum. The design was not adequate.
 Human Factor:
 The Technician did not refer to the IPC, CMM or AMM for instruction and had over-
confidence in his knowledge and experience.
 The Technician continued to work in awkward position.
 The Technician was under time constraints to get the task completed prior to the
flight the following morning
 System Factor:
 The critical task was not inspected and verified by second person.

HUMAN FACTORS: PERSONAL
INFLUENCE & FACTORS
 COMPLACENCY
 DISTRACTION
 PRESSURE
 LACK OF RESOURCES
 LACK OF KNOWLEDGE
 POOR AWARENESS
 STRESS
 FATIGUE
 POOR COMMUNICATION
 LACK OF ASSERTIVENESS
 LACK OF TEAMWORK
 DEPENDANCE ON NORMS

COMPLACENCY
What is Complacency?
 The feeling that you know everything about a subject or situation
“I’ve being doing this for years, I don’t need any manuals or
training”,
 Complacency causes: accidents, loss of profit, damaged
equipment.

COMPLACENCY
Solutions to Complacency are:
 Always follow the checklist or work cards,
 Never work from memory,
 Be sure to vary your routine periodically,
 Be aware of the dangers of complacency,
 Recurrent training and Human Factors programs.

DISTRACTION
What is Distraction?
 It is a loss of concentration on the task,
 The human brain is a problem-solving machine, so people find
routine tasks boring. In search of stimulation the mind wanders to
find something interesting and fun.

DISTRACTION
Solutions to Distraction are:
 Use a detailed check list,
 Always finish the job,
 Double inspect the work,
 Record or tag uncompleted work,
 When you go back to the job, always go back three (3) steps,
 Recurrent training and Human Factors.

PRESSURE
What is Pressure?
 It’s the feeling that “it’s all to much”, “I can’t do it on time”, “I
can’t tell anyone”,
 Pressure causes: stress, increased safety risks, loss of profit through
sick time and lower efficiency.

PRESSURE
Solutions to Pressure are:
 STOP! Assess the situation,
 LOOK! at the situation rationally;
 Can I safely do the job on time?
 Have I voiced my concerns clearly?
 What is the worst thing that can happen to me?
 LISTEN! to your rational mind,
 ACT! Speak up, ask for help or time,
 Recurrent training and Human Factors programs.

LACK OF RESOURCES
What is Lack of Resources?
 Not having the right tools to do the job,
 Lack of resources causes: wasted man hours, loss of profit,
stressed workers.

LACK OF RESOURCES
Solutions To Lack of Resources:
 Check all suspect areas at the beginning of all inspections and
AOG the required parts,
 Order & stock parts before they’re required,
 Know your sources, arrange for pooling and/or loaning,
 Maintain aircraft to the highest standards, if in doubt check,
 Initial and recurrent training programs.

LACK OF KNOWLEDGE
What is Lack of Knowledge?
 Not having the knowledge, skill or experience to do the job,
 Lack of knowledge causes: wasted resources, accidents,
unhappy stressed workers.

LACK OF KNOWLEDGE
Solutions to Lack of Knowledge are:
 Obtain school training on type, and model,
 Get supervised OJT,
 Use current manuals, old data doesn’t cut it!
 Tech Rep’s are there for a purpose...use them,
 Initial and recurrent training programs.

LACK OF AWARENESS
What Is Lack of Awareness?
 Not focusing of the world around you,
 Lack of Awareness causes accidents, damaged equipment,
wasted man hours.

LACK OF AWARENESS
Solutions to Lack of Awareness are:
 THINK... what could occur in the event of an accident?
 CHECK... will your work conflict with a previous or existing repair
a/o modification?
 ASK... see if anyone else can spot a problem you overlooked,
 Human Factors and recurrent training programs.

STRESS
What Is Stress?
 It is over reacting physically and emotionally to external and
internal pressures,
 Stress can cause physical and emotional illnesses,
 STRESS leads to DISTRESS.

STRESS
Solutions to Stress are:
 STOP! burning up emotional energy,
 LOOK! rationally at the problem,
 LISTEN! to your rational not emotional mind
 ACT! once you have a plan, do it!
 Human Factors and recurrent training programs
If you don’t manage stress, it will manage YOU!

STRESS
Other solutions and stress helpers are:
 Be sure the solution starts with “I”,
 Be realistic and practical,
 TAKE A BREAK!!
 Talk to someone who is not emotionally involved with the problem,
 Don’t expect miracles, just keep trying,
 Exercise, good diet and relaxation,
 At all times “manners maketh the man” a polite word and a smile
can solve most of the stress problems in a working environment.

FATIGUE
What is Fatigue ?
 Fatigue is the body’s normal reaction to a physical or mental
stress of a prolonged duration.
 Fatigue causes: physically and emotionally drained and unable
to carry out the job.
 There are two types of fatigue:
 Acute - short duration, cured with good nights sleep,
 Chronic - occurs over a period long period of time, long
recovery.

FATIGUE
Causes of Fatigue are:
 Long hours of labour/work
 Stress of high intensity,
 Large temperature variations,
 Noise - above 80dB for long duration,
 Vibration for long periods and sufficient intensity,
 Strong lighting.

FATIGUE
Symptoms of Fatigue;
 Enhanced stimulus required in order to respond,
 Attention reduced,
 Memory diminished,
 Mood becomes withdrawn,
 Disrupted Circadian rhythm (time of day effect).

FATIGUE
Solutions to Fatigue are:
 Work sensible hours,
 Take break,
 Have an interest outside of work,
 Exercise, good diet and relaxation,
 Follow sensible health and safety regulations.

LACK OF COMMUNICATION
What is Communication?
 Passing on to others your meaning and intent.
 Lack of communication will cause: misunderstandings, wasted
hours of work, safety problems, stress.

“I have to tell you that what you heard and
what I said are two different things and what
you think I said is definitely not what I meant”
Sound familiar?

The secret to good communication:
 2 ears,
 2 eyes,
 1 mouth,
 Use them in that order!

Solutions to improve Communication:
 Learn to Listen
 Don’t:
 Debate,
 Detour,
 Pre-plan,
 Tune-out.
 Do:
 Ask questions,
 Paraphrase,
 Make eye contact,
 Use positive body language,
 Be aware of Human Factors!

LACK OF ASSERTIVENESS
What is Lack of Assertiveness?
 Not knowing when to say no!!
 Lack of assertiveness causes: lack of communication, safety risks
are increased, loss of profit

LACK OF ASSERTIVENESS
Solutions to Lack of Assertiveness are:
 Never answer a request immediately. Take a moment to breath,
think then reply,
 Record all the work you do in the log book, and only sign for
what you have done and seen,
 Refuse to compromise your standards,
 Human Factors development training.

LACK OF TEAMWORK
What is Lack of Teamwork?
 Not working together for a common goal,
 Lack of team work causes: loss of profit, inefficient operations,
stress on workers.

LACK OF TEAMWORK
Solutions to Lack of Teamwork are:
 Always discuss and plan the WHO, WHAT, WHEN, WHERE and
HOW the job is to be done,
 Ensure that everyone understands and agrees,
 Human Factors teamwork development training.

NORMS
What are norms?
 It’s a way of doing business that’s not approved but it’s been
done locally for so long it’s now a “norm’.
 Causes: inefficient operation, safety hazards, non compliance
with regulations

NORMS
Solutions to norms:
 ALWAYS work in accordance with the relevant manual,
 Be aware that “norms” doesn’t make it right,
 Recurrent training and Human Factors training programmes.

REASON’S MODEL
The Swiss Cheese model of accident causation, originally proposed by
James Reason, likens human system defences to a series of slices of
randomly-holed Swiss Cheese arranged vertically and parallel to each
other with gaps in-between each slice.
Reason hypothesizes that most accidents can be traced to one or
more of four levels of failure:
 Organisational influences,
 Unsafe supervision,
 Preconditions for unsafe acts, and
 The unsafe acts themselves.

REASON’S MODEL
 In the Swiss Cheese model, an organisation's defences against
failure are modelled as a series of barriers, represented as slices
of the cheese. The holes in the cheese slices represent individual
weaknesses in individual parts of the system, and are continually
varying in size and position in all slices. The system as a whole
produces failures when holes in all of the slices momentarily align,
permitting "a trajectory of accident opportunity", so that a
hazard passes through holes in all of the defences, leading to an
accident.

HUMAN FACTORS ANALYSIS AND
CLASSIFICATION SYSTEM (HFACS)
The Human Factors Analysis and Classification System (HFACS) was
developed by Dr Scott Shappell and Dr Doug Wiegmann. HFACS is
heavily based upon James Reason's swiss cheese model. The
HFACS framework provides a tool to assist in the investigation
process and target training and prevention efforts. Investigators are
able to systematically identify active and latent failures within an
organisation that culminated in an accident. The goal of HFACS is
not to attribute blame; it is to understand the underlying causal
factors that lead to an accident.

THE HFACS FRAMEWORK
The HFACS framework describes human error at each of four levels of
failure:
 unsafe acts of operators(e.g., aircrew),
 preconditions for unsafe acts,
 unsafe supervision, and
 organisational influences.
Within each level of HFACS, causal categories were developed that
identify the active and latent failures that occur. In theory, at least one
failure will occur at each level leading to an adverse event. If at any
time leading up to the adverse event, one of the failures is corrected,
the adverse event will be prevented.

HFACS LEVEL 1: UNSAFE ACTS
The Unsafe Acts level is divided into two categories - errors and
violations - and these two categories are then divided into
subcategories. Errors are unintentional behaviours, while violations
are a wilful disregard of the rules and regulations.

Errors:
 Skill-Based Errors: Errors which occur in the operator’s execution of a
routine, highly practiced task relating to procedure, training or
proficiency and result in an unsafe situation (e.g., fail to prioritise
attention, checklist error, negative habit).
 Decision Errors: Errors which occur when the behaviours or actions of
the operators proceed as intended yet the chosen plan proves
inadequate to achieve the desired end-state and results in an
unsafe situation (e.g, exceeded ability, rule-based error,
inappropriate procedure).
 Perceptual Errors: Errors which occur when an operator's sensory
input is degraded and a decision is made based upon faulty
information.

Violations:
 Routine Violations: Violations which are a habitual action on the
part of the operator and are tolerated by the governing
authority.
 Exceptional Violations: Violations which are an isolated departure
from authority, neither typical of the individual nor condoned by
management.

HFACS LEVEL 2: PRECONDITIONS FOR
UNSAFE ACTS
The Preconditions for Unsafe Acts level is divided into three categories:
 environmental factors,
 condition of operators, and
 personnel factors.
These three categories are further divided into subcategories.
Environmental factors refer to the physical and technological factors that affect practices,
conditions and actions of individual and which result in human error or an unsafe situation.
Condition of operators refers to the adverse mental state, adverse physiological state, and
physical/mental limitations factors that affect practices, conditions or actions of individuals and
result in human error or an unsafe situation.
Personnel factors refer to the crew resource management and personal readiness factors that
affect practices, conditions or actions of individuals, and result in human error or an unsafe
situation.

UNSAFE ACTS

UNSAFE ACTS
Environmental Factors:
 Physical Environment: Refers to factors that include both the
operational setting (e.g., weather, altitude, terrain) and the
ambient environment (e.g., heat, vibration, lighting, toxins).
 Technological Environment: Refers to factors that include a
variety of design and automation issues including the design of
equipment and controls, display/interface characteristics,
checklist layouts, task factors and automation.

UNSAFE ACTS
Condition of Operators
 Adverse Mental State: Refers to factors that include those mental
conditions that affect performance (e.g., stress, mental fatigue,
motivation).
 Adverse Physiological State: Refers to factors that include those
medical or physiological conditions that affect performance
(e.g, medical illness, physical fatigue, hypoxia).
 Physical/Mental Limitations: Refers to the circumstance when an
operator lacks the physical or mental capabilities to cope with a
situation, and this affects performance (e.g., visual limitations,
insufficient reaction time).

UNSAFE ACTS
Personnel Factors
 Crew Resource Management: Refers to factors that include
communication, coordination, planning, and teamwork issues.
 Personal Readiness: Refers to off-duty activities required to
perform optimally on the job such as adhering to crew rest
requirements, alcohol restrictions, and other off-duty mandates.

HFACS LEVEL 3: UNSAFE SUPERVISION
The Unsafe Supervision level is divided into four categories.
 Inadequate Supervision: The role of any supervisor is to provide
their staff with the opportunity to succeed, and they must provide
guidance, training, leadership, oversight, or incentives to ensure
the task is performed safely and efficiently.
 Plan Inappropriate Operation: Refers to those operations that
can be acceptable and different during emergencies, but
unacceptable during normal operation (e.g., risk management,
crew pairing, operational tempo).

 Fail to Correct Known Problem: Refers to those instances when
deficiencies are known to the supervisor, yet are allowed to
continue unabated (e.g, report unsafe tendencies, initiate
corrective action, correct a safety hazard).
 Supervisory Violation: Refers to those instances when existing rules
and regulations are wilfully disregarded by supervisors (e.g.,
enforcement of rules and regulations, authorized unnecessary
hazard, inadequate documentation).

HFACS LEVEL 4: ORGANISATIONAL
INFLUENCES
The Organisational Influences level is divided into three categories:
 Resource Management: Refers to the organisational-level
decision-making regarding the allocation and maintenance of
organisational assets (e.g., human resources, monetary/budget
resources, equipment/facility recourse).
 Organisational Climate: Refers to the working atmosphere within
the organisation (e.g., structure, policies, culture).
 Operational Process: Refers to organisational decisions and rules
that govern the everyday activities within an organisation (e.g.,
operations, procedures, oversight).

HFACS LEVEL 4: ORGANISATIONAL
INFLUENCES

SHEL MODEL INTRODUCTION
 70% of aviation accidents are a result of human error.
 Examples of human error are Pilot error (decision making), poor
maintenance practices etc.
 If 70% of aviation accidents are caused by human error, what are
the other 30% caused by?

SHEL MODEL
The most common answer is that these are down to technical
failures. However, machines don’t fail by themselves. If part of an
aircraft breaks it is either because it has been designed incorrectly
(the design is insufficient for its intended purpose), it has been built
or maintained incorrectly or has been used in the wrong way.
When you probe into the “technical accidents”, human error will
be involved somewhere. With the possible exception of a
completely freak accident that no one could possibly predict (e.g.
a plane being hit by a falling meteorite), every accident, incident
and near miss will have some element of human involvement in the
sequence of events leading up to it.

SHEL MODEL
We have mentioned humans, machines and procedures. Within
organisations, these components come together to form systems.
Systems are groups of components working together towards a
common goal. During the 1970s, this idea of systems was expanded
to cover human factors in the aviation industry and led to the
development of the SHEL model, SHEL being the acronym of its 4
component types as shown.

SHEL MODEL
 SOFTWARE: Procedures
 HARDWARE: Machinery, Equipment etc.
 ENVIRONMENT:
 LIVEWARE: Humans
All 4 components of the model make up
any given system.

SHEL MODEL
 The environment refers to the physical environment, the liveware
refers to the human components, hardware refers to the machine
components and software refers to any procedures. As you can see
from the diagram, there is liveware at the centre of the model. This
liveware is the human operators whose job we are looking at. That
human operator will need to interact with machines (hardware),
with procedures (software) and with other people (liveware). All of
this is done in some sort of environment. Aside from the teasing out
the individual component types that are present within most systems,
the real insight that the original designers of this model had was to
highlight the interfaces between components, i.e. the points where
the squares touch. As well as wanting to optimise the components
themselves, we also need to consider how we can optimise
the interfaces between components.

Human factors in Aviation

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