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CHAPTER 14. HUMAN FACTORS IN AVIATION
- -deals with the
- - physiological,
- -social, and
- -safety issues of the human and the system that he/she works in.
The International Civil Aviation Organisation (ICAO) states:
?Human Factors is about people: it is about people in their working and living environments, and it is about their relationship with equipment, procedures, and the environment. Just as importantly, it is about their relationships with other people?. Its two objectives can be seen as safety and efficiency.jQuery110107450981708473836_1488025881037 ?(ICAO Circular 227)
The human element includes pilots, non?pilot aircrew, maintenance workers, management and all others in the aviation community. It is the most flexible, adaptable and valuable part of the aviation system, but it is also the most vulnerable to influences that can adversely affect its performance.
Issues that should be included as part of a study of Human Factors includes:
- a) Health,
- b) Skill level,
- c) Decision making,
- d) Fatigue, and
- e) Emotional well being.
BECOMING A COMPETENT AIRCREW MEMBER
- dependent upon a combination of learning and training.
- Factors that may interfere with the success of the training include:
- a) Level of general health,
- b) Fatigue or discomfort,
- c) Emotional well being,
- d) Level of motivation,
- e) Quality of instruction
- f) Suitability of instructor,
- g) Skill level,
- h) Learning techniques,
- i) Communication styles, and
- j) Accident statistics.
Human actions are cited as causal factors in the majority of aircraft accidents and incidents.
- Over the past 60 years, 70?80% of accidents and incidents have been associated with the human element.
- Large proportions of these accidents and incidents could have been prevented through the proper application of Human Factors principles. Figure 14?1 graphically shows the impact of Human Factors on aircraft accidents.
- If the accident or incident rate is to be decreased, human factors must be better understood and the knowledge more broadly applied.
- The expansion of human factors awareness presents the international aviation community with the single most significant opportunity to make aviation both safer and more efficient.
It is difficult to improve on the ICAO description of the SHELL model which is clear and concise, so Figure 14?2 below is a replication from the ICAO Human Factors Digest No. 1.
The SHELL concept (the name being derived from the initial letters of its components: Software, Hardware, Environment, Liveware) was developed by Edwards in 1972 with a modified diagram to illustrate the model developed by Hawkins in 1975. For those familiar with the concept of ?man?machine?environment?, the following interpretations are suggested:
S: software (procedures, symbology, etc),
- H: hardware (machine),
- E: environment (the situation in which the L?H?S system must function), and
- L: liveware (human).
This building block diagram does not cover the interfaces that are outside Human Factors (hardware?hardware, hardware?environment and software?hardware), and is only intended as a basic aid to understanding Human Factors.
In the SHELL Model the match or mismatch of the blocks (interface) is just as important as the characteristics of the blocks themselves. A mismatch can be a source of human error. The model neatly ties back to the ICAO definition of Human Factors
- - hub of the SHELL model of Human Factors and is
- - identified as the person,
- -the most critical and most flexible component in the system.
- -In spite of this, humans are subject to considerable variations in performance and suffer many limitations, most of which are now predictable in general terms.
- -The remaining components must be adapted and matched to this central component.
This interface is the one most commonly considered when speaking of human?machine systems, some of which are:
- a) design of seats to fit the sitting characteristics of the human body,
- b) design of displays to match the sensory and information processing characteristics of the user,
- c) design of controls with proper movement, and
- d) coding and location.
The user may never be aware of a Liveware?Hardware deficiency, even where it finally leads to disaster.
- This is because the natural human characteristic is one of adapting to Liveware?Hardware mismatches, masking such a deficiency; this however will not remove its existence.
- This constitutes a potential hazard to which designers should be alert.
This encompasses humans and the non?physical aspects of the system such as:
- b) manual and checklist layout,
- c) symbology, and
- d) computer programs.
The problems are often less tangible in this interface and are consequently more difficult to resolve (for example, misinterpretation of checklists or symbology).
- The human?environment interface was one of the earliest recognised in flying.
- Initially, the measures taken all aimed at adapting the human to the environment (helmets, flying suits, oxygen masks, anti?G suits).
- Later, the trend was to reverse this process by adapting the environment to match human requirements (pressurisation and air?conditioning systems, soundproofing etc.).
Today, new challenges have arisen,
- - notably ozone concentrations
- -radiation hazards at high altitudes and
- -the problems associated with disturbed biological rhythms (sleep disturbance and deprivation as a consequence of the increased speed of trans?meridian travel).
Since illusions and disorientation are at the root of many aviation accidents the Liveware?Environment interface must consider perceptual errors induced by environmental conditions (eg, illusions during approach and landing phases).
The aviation system operates within the context of broad political and economical constraints, with those aspects of the environment interacting in this interface. Although the possibility of modifying these influences is beyond Human Factors practitioners, their incidence is central and should be properly considered and addressed by those in management with the possibility to do so.
- - interface between people.
- -Aircrew training and
- -proficiency testing have traditionally been done on an individual basis.
If each individual crewmember was proficient and effective, then it was assumed that the team consisting of these individuals would be proficient and effective also. This is not always the case however, and for many years, attention has increasingly turned to the breakdown of teamwork.
Flight crews function as groups and group influences play a role in determining behaviour and performance. In this interface, areas of concern are:
- a) leadership,
- b) crew cooperation, c) teamwork, and
- d) personality interactions.
The ICAO Human Factors Digest No. 2 describes current industry approaches to deal with this interface and covers Cockpit Resource Management (CRM) and Line Oriented Flight Training (LOFT) programs. Staff/management relationships are also within the scope of this interface, as corporate climate and company operating pressures can significantly affect human performance. Digest No. 2 also demonstrates the important role of management in accident prevention.
ADDITIONAL COMPONENTS OF THE ?SHELL? MODEL
The edges of this block are not simple and straight. As such, the other components must be carefully matched if stress in the system and eventual breakdowns are to be avoided.
In order to achieve this matching, an understanding of the characteristics of this central component is essential. Some of the more important characteristics include:
Physical size and shape: In the design of any workplace and most equipment, a vital role is played by body measurements and movements which will vary according to age, ethnicity and gender groups. Decisions must be made at an early stage in the design process with data being obtained from anthropometry and biomechanical measurements.
Physical Needs: The physical needs required by humans such as oxygen, food and water are obtained from physiology and biology.
Input Characteristics: Humans have sensory systems that collect information from their environment enabling them to respond to external events and carry out required tasks. All senses are subject to degradation for one reason or another and the sources of knowledge here are physiology, sensory psychology and biology.
Information Processing: These human capabilities have severe limitations. Poor instrument and warning system design has frequently resulted from a failure to take into account the capabilities and limitations of the human information processing system. Short and long?term memories are involved as well as motivation and stress. Psychology is the source of background knowledge in this area.
Output Characteristics: Once information is sensed and processed, messages are sent to the muscles from the brain to initiate the desired response, whether it be a physical control movement or the initiation of some form of communication. Acceptable control forces and direction of movement have to be known, and biomechanics, physiology and psychology provide such knowledge.
Environmental Tolerances: Temperature, pressure, humidity, noise, time of day, light and darkness can all be reflected in performance and well being. Enclosed spaces, heights and a boring or stressful working environment can also be expected to influence behaviour and performance. Information provided here is through physiology and psychology.
CLASSIFYING HUMAN FAILURES
- - unsafe acts involving the ?active? participation of the front line operators (aircrew, air traffic controllers, etc.) that have an immediate impact.
- -quite common
- - may, or may not, cause an accident or incident.
- Statistically, millions of crew errors are made before a major aircraft accident occurs.
- -are those errors that are made at some distant time/place before the accident or incident;
- -thus having a delayed impact on the operation.
- -Often managers, supervisors, decision?makers, etc, make this type of mistake.
- They can cause an accident or incident without involving active errors.
- -arise primarily from informational problems, such as forgetting, inattention, or incomplete knowledge, and are unintended.
- -reduced by improving the quality and availability of necessary information.
RULE BASED ERRORS
Humans are very good at making rapid and automatic assessments of complex situations by matching features and patterns with previously stored memories. The usual thought process is: if X then do Y. Unfortunately good rules can be misapplied, contraindications not noticed, or a bad rule may simply go uncorrected over time.
- When situations arise outside a person?s experience or training, one has to resort to slow and laborious problem? solving from first principles. Capacity for conscious thought is resource limited, attending to only one or two discreet items at a time. The mental model for the situation is often incomplete or incorrect.
- Also humans have a tendency to fixate on a particular hypothesis and select features from the world that support it. This has been termed ?confirmatory bias?.
SLIPS/LAPSES VS ERRORS.
- - failure of execution,
- -where the plan is adequate but the associated actions do not go according to plan.
- - Slips are observable actions often associated with a failure of attention,
- -while a lapse is an omission more often related to a failure of memory.
- These errors often occur during the performance of routine tasks in familiar surroundings, and may be provoked by some sort of change.
- - deliberate deviations from safe operating practices.
- - often associated with motivational problems such as low morale, poor role models, or failure to reward compliance. -often occur in a regulated social context.
James Reason proposed a model for thinking about human error in 1990, which has also become a classic way of analyzing ?organisational accidents?. The model describes four levels of human failure as shown in Figure 14?3.
Working backwards from the accident, the first level depicts the Unsafe Acts of the operators/aircrew that ultimately lead to the accident. These unsafe acts are the result of active failures on the part of the aircrew, for example failing to adequately scan instruments while flying in IMC. The importance of this model is that it does not just focus on these unsafe acts, traditionally called ?pilot error?, but rather also examines the latent failures which exist with the accident causation chain. Preconditions for unsafe acts refers to the influences that affect aircrew performance, such as fatigue, poor communication, or other environmental influences impacting physiology such as hypoxia. Performance degradation caused by these preconditions will result in the active failures which prompt unsafe acts. The third level of failure is also latent, called Unsafe Supervision. This addresses the underlying causes that set up the preconditions for unsafe acts. For example, poor management practices in maintenance may result in an aircraft system failure, which the aircrew have not been adequately trained to deal with. In a sense the operators are ?set up to fail? by latent failures of supervision. The organization and its culture can impact on performance at all levels, and this is reflected in the fourth layer of the model, Organisational Influences. The political, budgetary and regulatory environment in which an aviation system operates will determine the organisation?s policies with respect to any number of safety critical functions, such as maintenance. Thus Reason?s ?Swiss Cheese? model looks at failure and accident causation not just from the perspective of human error but also from the perspective of latent failures and conditions within an organisation that can predispose to an accident occurring.