[Slide #3]
Human Factors Analysis and Classification System (HFACS), by Scott Shappell
and Douglas Wiegmann |
1. Error
Classification
Drawing upon the work of Dr. James Reason (1990), Scott Shappell and
Douglas Wiegmann developed the Human Factors Analysis and Classification
System (HFACS) where human error can be described at each of four levels:
- Unsafe acts of aircrew;
- Preconditions for unsafe acts;
- Unsafe supervision; and
- Organizational influences.
Unsafe acts of aircrew
The unsafe acts of pilots can be loosely classified into one of two
categories:
(While both are common within most settings, they differ markedly when the
rules and regulations of an organization are considered. That is, errors can be
described as those “legal” activities that fail to achieve their intended outcome,
while violations are commonly defined as behaviour that represents the willful
disregard for the rules and regulations.
Three types of errors are identified
- Decision;
- Skill-based; and
- Perceptual.
Violations, on the other hand are classified as either:
Errors
One of the more common error forms, decision errors, represents
conscious, goal-intended behaviour that proceeds as designed; yet, the plan proves
inadequate or inappropriate for the situation. Often referred to as “honest
mistakes,” these unsafe acts typically manifest as poorly executed procedures,
improper choices, or simply the misinterpretation or misuse of relevant
information.
In contrast to decision errors, the second error form, skill-based
errors, occurs with little or no conscious thought. Just as little thought
goes into turning one’s steering wheel or shifting gears in an automobile, basic
flight skills such as stick and rudder movements and visual scanning often occur
without thinking. The difficulty with these highly practised and seemingly
automatic behaviours is that they are particularly susceptible to attention and/or
memory failures. As a result, skill-based errors, such as the breakdown in visual
scan patterns, inadvertent activation/deactivation of switches, forgotten
intentions, and omitted items in checklists, often appear. Even the manner
(or skill) with which one flies an aircraft (aggressive, tentative, or controlled)
can affect safety.
While decision and skill-based errors have dominated most accident
investigations, the third and final error form, perceptual errors,
has received comparatively less attention. No less important, perceptual errors
occur when sensory input is degraded, or “unusual,” as is often the case when
flying at night, in the weather, or in other visually impoverished environments.
Faced with acting on imperfect or less information, pilots run the risk of
misjudging distances, altitude, and descent rates, as well as responding
incorrectly to a variety of visual/vestibular illusions.
Violations
Although there are many ways to distinguish among types of violations, two
distinct forms have been identified. The first, routine violations,
tends to be habitual by nature and is often enabled by a system of supervision and
management that tolerates such departures from the rules. Often referred to as
“bending the rules,” the classic example is that of the individual who drives
his/her automobile consistently 5-10 kph faster than allowed by law. While
clearly against the law, the behaviour is, in effect, sanctioned by local
authorities, which will often not enforce the law until speeds in excess of
10 kph over the posted limit are observed. |
[Slide #5] |
2. Latent Conditions
According to Shappell and Wiegmann, the unsafe acts of aircrew are shaped by
three large organizational factors:
- Preconditions for unsafe acts;
- Unsafe supervision; and
- Organizational influences.
Preconditions for unsafe acts
Simply focusing on unsafe acts, however, is like focusing on a patient’s
symptoms without understanding the underlying disease state that caused them.
As such, investigators must dig deeper into the preconditions for unsafe acts.
Two major subdivisions of unsafe acts are:
- The substandard conditions; and
- The substandard practices.
Substandard conditions of the aircrew
Being prepared mentally is critical in nearly every endeavour; even more so in
aviation. With this in mind, the first of three categories, adverse mental
states, was created to account for those mental conditions that adversely
affect performance. Principle among these are the loss of situational awareness,
mental fatigue, circadian dysrhythmia, and pernicious attitudes, such as
overconfidence, complacency, and misplaced motivation, that negatively affect
decisions and contribute to unsafe acts.
Equally important, however, are those adverse physiological
states that preclude the safe conduct of flight. Particularly important
to aviation are conditions such as spatial disorientation, visual illusions,
hypoxia, illness, intoxication, and a whole host of pharmacological and medical
abnormalities known to affect performance. For example, it is not surprising that,
when aircrews become spatially disoriented and fail to rely on flight
instrumentation, accidents can, and often do, occur.
Physical and/or mental limitations of the pilot, the third and
final category of substandard condition, include those instances when necessary
sensory information is either unavailable or, if available, individuals simply do
not have the aptitude, skill, or time to safely deal with it. For aviation, the
former often includes not seeing other aircraft or obstacles because of the size
and/or contrast of the object in the visual field. However, there are many times
when a situation requires such rapid mental processing or reaction time that the
time allotted to remedy the problem exceeds human limits (as is often the case
during nap-of-the-earth flight). Nevertheless, even when favourable visual cues or
an abundance of time is available, there are instances when an individual simply
may not possess the necessary aptitude, physical ability, or proficiency to
operate safely.
Substandard practices of the aircrew
Often times, the substandard practices of aircrew will lead to the conditions
and unsafe acts described earlier. For instance, the failure to ensure that all
members of the crew are acting in a co ordinate manner can lead to confusion
(adverse mental state) and poor decisions in the cockpit. Crew resource
mismanagement, as it is referred to here, includes the failures of both inter-
and intra-cockpit communication, as well as communication with ATC and other
ground personnel. This category also includes those instances when crewmembers
do not work together as a team, or when individuals directly responsible for the
conduct of operations fail to co ordinate activities, before, during and after a
flight.
Equally important, however, individuals must ensure that they are adequately
prepared for the flight. Consequently, the category of personal readiness was
created to account for those instances when rules, such as disregarding crew rest
requirements, violating alcohol restrictions, or self-medicating, are not adhered
to. However, even behaviours that do not necessarily violate existing rules or
regulations (e.g., running ten miles before piloting an aircraft or not observing
good dietary practices) may reduce the operating capabilities of the individual
and are, therefore, captured here.
Unsafe supervision
Clearly, aircrews are responsible for their actions and, as such, must be held
accountable. However, in many instances, they are the unwitting inheritors of
latent failures attributable to those who supervise them. Failures included
inadequate supervision, planned inappropriate operations, failure to correct known
problems, and supervisory violations.
Inadequate supervision refers to failures within the
supervisory chain of command that were a direct result of some supervisory action
or inaction. In other words, supervisors must at least provide the opportunity for
individuals to succeed. It is expected, therefore, that individuals will receive
adequate training, professional guidance, oversight, and operational leadership,
and that all will be managed appropriately. When this is not the case, aircrews
are often isolated, as the risk associated with day-to-day operations invariably
will increase.
However, the risk associated with supervisory failures can come in many forms.
Occasionally, for example, the operational tempo and/or schedule is planned such
that individuals are put at unacceptable risk and, ultimately, performance is
adversely affected. As such, planned inappropriate operations
account for all aspects of improper or inappropriate crew scheduling and
operational planning, which may focus on such issues as crew pairing, crew rest,
and managing the risk associated with specific flights.
The remaining two categories of unsafe supervision, the failure to
correct known problems and supervisory violations, are
similar, yet considered separately. The failure to correct known problems refers
to those instances when deficiencies among individuals, equipment, training, or
other related safety areas are known to the supervisor but are allowed to continue
uncorrected. For example, the failure to consistently correct or discipline
inappropriate behaviour certainly fosters an unsafe atmosphere but is not
considered a violation if no specific rules or regulations were broken.
Supervisory violations, on the other hand, are reserved for those instances
when supervisors when managing assets willfully disregard existing rules and
regulations. For instance, permitting aircrews to operate aircraft without current
qualifications or licences is a flagrant violation that invariably sets the stage
for the tragic sequence of events that predictably follows.
Organizational influences
Fallible decisions of upper-level management can directly affect supervisory
practices as well as the conditions and actions of the crews. Unfortunately,
these organizational influences often go unnoticed or unreported
by even the best-intentioned accident investigators.
Traditionally, these latent organizational failures generally revolve around
three issues:
- resource management;
- organizational climate; and
- operational processes.
Resource management refers to the management, allocation, and
maintenance of organizational resources, including human resource management
(selection, training, staffing), monetary safety budgets, and equipment design
(ergonomic specifications). In general, corporate decisions about how such
resources should be managed centre around two distinct objectives safety
and on-time, cost-effective operations. In times of prosperity, both objectives
can be easily balanced and satisfied in full. However, there may also be times of
fiscal austerity that demand some give and take between the two. Unfortunately,
history tells us that safety is often the loser in such battles because safety and
training are often the first to be cut in organizations experiencing financial
difficulties.
Organizational climate refers to a broad class of
organizational variables that influence workers’ performance and is defined as the
situational-based consistencies in the organization’s treatment of individuals One
telltale sign of an organization’s climate is its structure, as reflected in the
chain-of-command, delegation of authority and responsibility, communication
channels, and formal accountability for actions. Just like in the cockpit,
communication and co ordination are vital within an organization. However, an
organization’s policies and culture are also good indicators of its climate.
Consequently, when policies are ill defined, adversarial, or conflicting or when
they are supplanted by unofficial rules and values, confusion abounds, and safety
suffers within an organization because of human errors.
Finally, operational process refers to formal processes
(operational tempo, time pressures, production quotas, incentive systems,
schedules, etc.), procedures (performance standards, objectives, documentation,
instructions about procedures, etc.), and oversight within the organization
(organizational self-study, risk management, and the establishment and use of
safety programs). Poor upper-level management and decisions concerning each of
these organizational factors can also have a negative, albeit indirect, effect on
personnel, individual performance and system safety.
What are the inferences that can be made from the term pilot
error?
Human error when the outcome of something we did or
didn’t do is not what we expected.
- Selected the wrong switch
- Used the wrong procedure
- Overlooked something, failing to spot a problem
- Forgot to pass on a message
- Sent the wrong information
Human Error (cause identified)
- air traffic controller error (ATC)
- improper loading of the aircraft (Loader)
- fuel contamination (Refueller)
- improper maintenance (aircraft maintenance engineer (AME))
Why is the term pilot error distinct from human error?
The term pilot error is a statement of liability or causal factor in
the occurrence. Finding that the pilot was a fault can infer skill deficiency and
suggests that further training is required.
Pilot error can often overshadow human error (e.g., maintenance)
Pilot error can preclude the fixing of a faulty system, rather than a skill
deficiency; it may be required to fix a faulty system.” The occurrence could have
been the result of inadequate training or “improper” maintenance.
The causal factor being pilot error usually terminated the investigation. It
didn’t threaten the administration, and often shut the door to addressing the real
fault or problem.
There was a time in the investigation of aircraft accidents and near-accidents
when the cause would often be attributed to “pilot error.” Even correct, this
diagnosis wasn’t very helpful in preventing other accidents. It wasn’t until
recently that investigators began to ask why the pilot erred in the first place.
It didn’t take long to notice that bad decisions were often the cause and to
realize that if pilots could be taught to make better decisions, they would be
safer pilots. Pilot error is not the cause of an accident. The cause is to be
found in whatever it was that interfered with the pilot’s decision at a critical
moment, the outcome of which was pilot error.
Human errors contribute significantly to aviation accidents. Stressors like
overwork, boredom, noise, heat distractions, deadlines, and fatigue are not the
whole story, although they expose weaknesses in procedures, documentation,
communication, and decision-making processes, to name a few.
Even the most competent and well-motivated individuals make errors.
Aren’t some people prone to error?
Some people are more prone to make certain kinds of errors or are more
vulnerable to particular risk factors, but nobody is perfect. It is unrealistic
to rely on those who are less vulnerable to always avoid error; it is only a matter
of degree. So if to err is human isn’t error inevitable? You don’t have to learn by
trial and error, or just hope for the best. A lot of good practices that can reduce
the risk of human error exist, such as PDM. Just identify what is relevant to your
work and apply it.
What is a good practice?
Working practices and procedures designed to account for natural human
performance limitations and vulnerabilities.
Creating working conditions that minimize the effects of those limitations and
vulnerabilities. |