Every accident hides more than whom bears responsibility
Human Factors Factsheet
Every accident hides more than whom bears responsibility
Throughout the years human factors have become increasingly important in
the aviation industry (Figure 2). Since the introduction of human factors,
human errors have been appointed as one of the most common causes of
aviation accidents (Example 1). Research found that human error is a
symptom of trouble deeper inside a system. Investigations should avoid
attributing blame and need to look beyond human error, taking into account
the situation as a whole (Figure 1). In order to create an understanding of
human factors in aviation, three groups of human factors are discussed in
this factsheet. The first group consists of Human Limitations, which are
internal factors that adversely affect (cognitive) performance. The second
group consists of External Factors that adversely affect (cognitive)
performance. Finally, the third group are Organizational Factors, external
factors that to not directly affect cognitive performance.
Old View
Human error is a cause of
You must find people's:
-Inaccurate assessments
Example 1: September 17th, 2014
New View
A vacation flight from Ryanair performed by a Boeing 737-800 from Leeds
(UK) to Malaga (ES) was on final approach to Malaga intending to land on
runway 13. Meanwhile a Boeing 737-800 from Jet2 was departing from the
same runway. By the time the Jet2 aircraft was starting its roll the Ryanair
aircraft reached the runway. The Ryanair aircraft performed a go around
and both aircraft climbed out to a safe altitude. By this time the vertical
separation between the aircraft was only 400 ft. The problem was resolved
when the Ryanair aircraft made a 90 degree right turn. While the Jet2
aircraft continued the standard climb out.
Human error is a symptom of
trouble deeper inside a system
To explain failure, do not try to
find where people went wrong
-Wrong decisions
The CIAIAC investigated any possible errors by the pilots, air traffic
controllers and other relevant factors that contributed to the incident. The
CIAIAC concluded that a lack of communication between pilots and air
traffic controllers, stress, fatigue, and a lack of awareness by air traffic
controllers can contribute to similar events in absence of technical failures 1.
-Bad judgements
To explain failure, you must
seek failure
Instead, find out how people's
assessments and actions made
sense at the time, given the
Figure 1, The new view (Dekker, 2002)
Human Factors Factsheet
1996 Boeing
introduces MEDA
Since WW II Human Factor research has become a more profound part of
aviation safety management. From the first flight control, flight operations,
ergonomic and psychological research, to implementation of knowledge on
the first jet aircraft in the 50’s, 60’s and 70’s. HF in accident analysis and
the influence of HF on performance and safety remained a smaller part of
research until the 1980’s.
1988 After Aloha
1977 After Spanish
CAA research, the
Air Line Pilots
reinvestigated the
accident to
determine the
influence of
Human Factors.
1977 KLM
FL4805 and Pan
Am 1736 collision
Combination of
conditions and
between KLM crew
and ATC caused
FL243 the FAA
was mandated to
investigate the
impact of Human
Factors in nearly all
areas in aviation
and focus on the
relation between
modernization of
systems and human
Valujet FL592
prompted the
FAA to start a
second regulatory
response in Human
factor research. The
new documentation
focussed on
adequately address
HF issues in
design, application
of technology,
systems, training,
and procedures
besides the
growing relevance
to maintenance.
1993-1994 FAA
implemented its
findings in Order
8300,10 of the
Handbook, Titled
‘’Human factors
Involved in
Inspection and
Repair in a Heavy
1988 Aloha
Airlines FL243
1996 ValuJet
decompression due
to fatigue damage
not noticed by
Aircraft crashed
due to improperly
packed oxygen
generators that
caused fire.
and PEAT (1999)
to systematically
investigate Human
Errors (Factors),
contributing causes
in maintenance and
flight crew
discover causes of
1999 Airbus
introduces FSF, to
encourage human
factors research
2000 Airbus EGIS
Human Factors
Cockpit support
Since 2005, FAA,
EASA and national
CAAs issue HF
requirements in
multiple aviation
2009 Integration of
Human Factors into
Systems (CAAP).
Figure 2: Evolvement of human factors in aviation
Human Factors Factsheet
effect on complacent behaviour. For example after a 12 hour overnight
flight, pilots become increasingly hesitant towards stimuli in the visual
field, and response times increase. Potential dangers go unnoticed 5, 6, 7. In
an attempt to prevent complacency researchers tested the effects of
training. Training did improve overall performance, but had no effect on
automation induced complacency 8, 9. Researchers do suggest that training
on attention allocation strategies could mitigate complacent behaviour 10.
Human Limitations
Humans have their limitations. The performance of humans differ when
they are exposed to factors such as stress. During an Air France flight from
Rio de Janeiro to Paris in 2009 the aircraft stalled in mid-flight and crashed
into the ocean. Although there were technical issues with the aircraft, it was
the pilot’s reaction to the situation that led to a stall. Even though aural and
visual stall warnings were presented, the pilot continued to pull the stick
backward, indicating that the pilot was focused on increasing the altitude of
the aircraft. Both pilots faced a number of human limitations resulting in the
crash. Surprisingly these limitations are present during normal operations
and can become critical even in a normal chain of events 2.
Inattentional Blindness
During everyday activities we seem to look without seeing every detail. A
pilot focusing his attention on the gauges may fail to notice unsuspected
objects on a runway when he looks through the windshield. This is called
Inattentional Blindness. Focusing attention on one activity also increases
the chance of being blind to changes: Change Blindness. Inattentional and
Change Blindness are explained by the limited amount of data a person is
able to process. During high demanding tasks there is less capacity left to
process changes in the direct environment 11. Also age is a factor in
Inattentional Blindness. Adults are less likely to encounter Inattentional
Blindness compared to children and elderly. Inattentional Blindness, like
Change Blindness and Inattentional Deafness, happens without being
noticed by the person. Therefore it is hard to fight Inattentional Blindness.
Only by the use of safety nets, such as a division between operational and
monitoring tasks, can Inattentional Blindness be countered.
Complacency is the uncritical satisfaction with oneself or one's
achievements and can lead to overreliance on an automated system. The
operator becomes less and less vigilant while monitoring 3. Complacency
can occur when an operator is multitasking in a highly reliable automated
environment and the operator blindly trusts the system 4. Fatigue has an
Inattentional deafness
Given the noise in the cockpit, it could occur that a pilot misses a warning
sound or part of a conversation. This can occur during demanding tasks and
is called Inattentional Deafness. The chance of suffering from Inattentional
Deafness varies with the amount of attention needed for the main task 12.
The chance of Inattentional Deafness is greater during a highly demanding
visual task 12, such as landing an aircraft and watching the instruments.
Inattentional Deafness can be reduced by assigning a clear division of tasks
and frequent general checks 13.
Human Factors Factsheet
Lack of assertiveness
External factors
Lack of assertiveness is a form of behaviour which occurs when a person is
not self-confident enough to speak up for his or her rights and ideas.
Researchers have shown that personality traits are determined by genetics:
of all the children who were very shy and introvert 25% will not change this
behaviour later in life 14. It has been shown that a gap in experience or
differences in military rank (the trans-cockpit authority gradient) influences
communicational behaviour. A steeper gradient is more likely to trigger
passive behaviour 15. Although lack of assertiveness is a global problem, the
impact can be correlated with the culture of the region. For example
Japanese people tend to be more passive than Israeli 16. Assertiveness can
be improved through group courses with role playing.
The Tenerife accident on March 27th, 1977, a runway collision between a
Boeing 747 of KLM and a Boeing 747 of Pan Am, led to one of the first
investigations where the contribution of human factors was studied. 583
people died during the crash. Human factors related to this accident include
stress and a lack of assertiveness. The stress of the KLM crew was initiated
by their duty time. The hierarchy in the cockpit of KL4805 adversely
affected the first officer’s assertiveness, making him reluctant to question
the captain’s decision to take off 19. The former shows that human
performance and judgement can be affected by external factors that lie
beyond influence and character of the individual.
Lack of communication
Lack of awareness
Lack of communication is a failure to transmit, receive, or provide enough
information to complete a task. Maintenance engineers, ground handlers, air
traffic controllers and pilots are as susceptible as anyone to unknowingly
submit to lack of communication. Lack of communication occurs when
people wrongly assume certain things have already been done or said 20.
One method to prevent a lack of communication is by using a safety net to
never assume a thing, always check with colleagues, and always build in
feedback. Besides this, important information should always be written
down so it cannot be forgotten 21.
Situation(al) Awareness is
stated as “the perception of
the elements in the
environment within a
volume of time and space,
the comprehension of their
meaning and the projection
of their status in the near
future” 17. A lack of
Situation Awareness has
been implicated in 85% of
all human factor incidents 18. Situation Awareness is obtained by scanning
the environment and comparing the gathered results with mental models.
Therefore, aspects as communication, coordination, objective setting and
feedback are essential. Situation Awareness is lost by distraction,
inattention and high workload. Loss of Situation Awareness is prevented by
implementing proven best practices, following ICAO recommendations and
company’s Standard Operating Procedures (SOPs).
Fatigue is physical and/or mental exhaustion 22, resulting in a decrement of
performance. Fatigue occurs in aviation due to irregular working hours and
long duty periods leading to circadian disruptions and insufficient sleep.
Pilots nap an average of between 1.8 and 3.7 hours of sleep on long-haul
flights 23. Fatigue studies show that besides permitted naps, sudden shifts
between wakefulness and sleep lasting a fraction of a second up to 30
seconds (microsleep) do occur in the cockpit. These microsleeps
particularly happen on long-haul flights during low-work periods. It is quite
possible that these microsleeps occur with both pilots at the same time,
Human Factors Factsheet
leaving the aircraft effectively uncontrolled. Pilots do not always notice
their level of fatigue, and may doze off repeatedly while believing to have
“successfully avoided the physiological realities of severe fatigue” 24.
Stress is the subconscious response to the demands placed upon a person 3.
Excessive stress leads to overburdening of abilities and decreases human
performance 25, 26. However, too little activation or arousal, which can be
seen as a low stress level, entails boredom which also leads to decreased
performance 27. Work related stressors can be tight deadlines, innovation,
(lack of) social support, work that requires a high attention level, or
repetitive tasks. Stressors can also alight from personal life: the passing
away of a family member or divorce 28, 29, 30. Stress management techniques
include relaxation techniques, careful regulation of sleep, a healthy diet, and
Distraction occurs when our attention is shifted away from the original focal
point. It is possible to discriminate four types of distraction: visual,
auditory, manual and cognitive distraction 18.. Distraction occurs because
our mind works much quicker than our hands and therefore we are always
thinking ahead 3, and depends on personality, physical circumstances and
the environment 31. Distractions can be countered by using a safety net
consisting of a few points to remember when working on a task, a detailed
check sheet at completion, marking any uncompleted work, and always
going back three steps when you return to the job. Let somebody else
inspect the work when it is finished, or double check it yourself 32. Training
may also help 3.
Organizational factors
During a Ryanair flight from Stockholm to Madrid on July 26th, 2011, the
aircraft had to divert due to thunderstorms. The pilots reported to ATC that
there was insufficient fuel to reach Madrid and had to land at Valencia.
Before the flight Ryanair introduced a new system to calculate the amount
of fuel required for a particular flight in order to increase fuel efficiency.
Pilots are always able to add extra fuel but should try to minimize the
amount of excess fuel. In this case the incident could have been prevented
by both pilots and management. Also the lack of resources regarding the
weather was involved in the incident. The human factors involved in this
incident did not affect human performance, but adversely affected safety by
imposing a restraining environment.
Human Factors Factsheet
Lack of teamwork
Lack of teamwork is defined as the presence of interdependent individuals
who do not work together or communicate well with others to achieve a
common set of goals 21. Lack of teamwork is caused by individuals that do
not communicate to their team members and/or do not know what their
roles and responsibilities are. Moreover, lack of teamwork can be caused by
taking individual rather than group decisions 21. Through the use of standard
operating procedures and formal training such as crew resource
management, commercial aviation regulations attempt to prevent accidents
where lack of teamwork is involved.
“Norms is short for ‘Normal’, or the way things actually are done around an
organization 3. They are unwritten rules followed or tolerated by the
majority of a group. Negative norms are those that detract from an
established safety standard. This kind of human error occurs mainly because
of the following points: routine work, alternative norms made by
employees, functioning in a non-approved manner. The points become
unofficial norms when they remain in the organization for an extended
period of time. In the end, management tolerates the norms that are made by
the employees 21. Countermeasures can be to never use shortcuts, be aware
of your own bad habits, emphasize positive things to eliminate negative
things, and be an example for other people. Finally, it is managements role
to correct employee behaviour directly when it is contrary to safety 21.
Lack of knowledge
A lack of knowledge indicates that one does not have the knowledge, skills
or experience to perform the job 34. For instance maintenance procedures on
aircraft must be performed in accordance with standards specified by
aircraft manufacturers, airlines or authorities (FAA, EASA and ICAO).
Changes in these procedures occur regularly. Management should invest in
regular training in order to keep employees up to date with the quickly
changing environment in aviation 35. Also the latest manuals must be
available to make sure that the right procedures are executed, and one
should ask help from others when something is unclear 34.
Lack of resources
Resources are any tools or materials required to maintain and/or inspect
aircraft. In order to prevent accidents due to a lack of resources, equipment
has to be ordered before it is required and the available sources for
equipment have to be known to arrange pooling or loaning. Furthermore,
the time schedule to complete an aircraft maintenance task must be
sufficient 33.
Pressure may be expected when working with various people and systems.
It is only when pressure builds to a certain level and stands in the way of
completing the necessary task timely and correctly that it becomes a threat
to safety. The most common form of pressure is time pressure 36. Research
shows that time pressure causes people to take more risks and more likely
make decisions based on heuristic recognition than use available knowledge
Human Factors Factsheet
37, 38
. Task difficulty and the available time need to be well regulated in
procedures to make sure employees are not under any kind of pressure when
performing the task. Organizational aspects like working hours should be
taken into account when designing solutions to reduce incidents and
accidents in aviation.
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Human Factors Factsheet
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Leveson, N. G. (2012). Engineering a safer world: Systems thinking applied to
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