Human Factors in Fatal Aircraft Accidents

Introduction

This analysis was conducted on the 75 fatal aeroplane accidents which occurred in the period 1 January 1988–31 December 1990. Seventy-four accidents involved general aviation aircraft and one accident involved a regional airline aircraft. One hundred and sixty-two deaths resulted from the accidents. Most of the accidents (57 of 75) involved single-engine aircraft. Accidents to rotary wing aircraft, gliders and sport aviation aircraft were excluded.

Type of operation

The largest proportion of accidents occurred on flights categorized as private or business. One accident in the sample occurred on a regional airline flight (low capacity airline).

Type of occurrence

Many accidents involve a sequence of events. The following graph indicates the first event in the accident sequence. Each event may have been followed by further events not reported here. For example, an aircraft which sustained an engine failure may have then been involved in a hard landing. The most frequent first event leading to fatal accidents was loss of control. The next most frequent first event was collision with terrain, control unknown where the investigation could not determine whether the pilot was in full control of the aircraft. Controlled impact with terrain refers to accidents in which the aircraft struck terrain while apparently under the control of the pilot. Such accidents typically occur in conditions of reduced visibility. Collided with object (not wires) includes cases in which an aircraft collided with trees, buildings or other obstructions. Collision with power lines is treated separately under wire strike.

Broad accident factors

Seventy-two per cent of the accidents were judged to involve pilot factors. Weather was a factor in 17% of the accidents. Other personnel contributed to 12% of the accidents. Other personnel refers to people other than the pilot of the aircraft, and includes air traffic controllers, other flight crew and maintenance workers. Note that accidents may be assigned multiple factors.

Pilot factors

Figure 4 indicates the most frequent pilot factors in the sample of accidents. The most commonly assigned factor was poor judgement. Other common factors were in-flight decisions or planning and attempted operation beyond experience or ability. These results are consistent with
the general worldwide finding that inadequate decision making contributes to a large proportion of accidents in general aviation and airline operations. Examples of inadequate decision making or poor judgement are knowingly continuing a flight into adverse weather, engaging in unauthorized low flying and continuing a flight with a known low fuel state. Medical factors were relatively rare. These factors included mismanagement of fuel system and selected unsuitable area for landing or takeoff.

Further detail on human factors terminology

Poor judgement

For many years it was assumed that good judgement was an inevitable by-product of flying experience. However, the data that BASI has accumulated indicates that errors of judgement are made by experienced and less-experienced pilots alike. Airlines around the world recognized in the 1970s that even experienced crews could make serious errors of judgement. For example in 1979, the crew of a United Airlines DC8 were distracted for so long by a landing gear problem that they eventually ran out of fuel1. Many major airlines have now introduced crew resource management (CRM) training to ensure that flight crew apply principles of judgement and teamwork. However, for general aviation and regional airline operations, pilot judgement continues to be a significant accident factor. In the 1980s, the Australian Department of Aviation and equivalent bodies in the USA and Canada sponsored the development of judgement training courses for pilots. The results indicated a significant reduction in aircrew errors 2)In 1987, the US Federal Aviation Administration (FAA) released a series of manuals oriented to the decision-making needs of general aviation pilots. 3)The FAA later released an advisory circular on the subject of aeronautical decision making.

Diverted attention

Pilots may divert their attention from the operation of the aircraft for a variety of reasons. Diverted attention is particularly likely when the pilot is under time pressure or stress. For example, a minor abnormality such as a landing gear warning may distract a pilot from other aspects of the flight. In the following example, an experienced pilot collided with powerlines which he was aware of. The investigators believed that his attention had been distracted.

In-flight decisions or planning

Problems with in flight decisions or planning include situations where a pilot elects to continue a flight with a known deficiency, continues a visual flight into adverse weather or makes a poorly planned approach to an airfield. The following example illustrates how inadequate in-flight decisions or planning can lead to an Accident.

Inadequate pre-flight preparation or planning

In many cases, the origins of the accident began well before the aircraft left the ground. Pre-flight preparation or planning includes the pre-flight check of the aircraft, flight planning and weather briefing. The fuel gauges of light aircraft can be unreliable and pilots are expected to
visually check the amount of fuel in the tanks before flight. The following example illustrates how a minor error during this pre-flight inspection apparently led to an in-flight fuel loss.

Conclusion

In conclusion, the largest proportion (36%) of fatal aircraft accidents occurred on private/ business flights. The three most frequent first events in accidents were loss of control, collision with terrain (control unknown) and wirestrike. Most accidents had more than one contributing factor, although pilot factors were involved in over 70% of fatal accidents. The most common pilot factors related to poor judgement and decision making. BASI experience has shown that errors of judgement can be made by experienced and inexperienced pilots. This report deals mainly with the human factors which relate to pilots. In recent years however, BASI has recognised that while pilot factors are of great importance, accidents frequently have their origins in the aviation system as a whole. Organisational factors such as training, supervision, regulation, commercial pressures and licensing are involved in a significant proportion of accidents. The investigation of these organisational or systemic factors now forms the basis of much of BASI’s investigation and research effort.

References
1. NTSB (1979). Aircraft accident report-United Airlines, Inc., McDonnell-Douglas DC-8-61, N8082U, Portland, Oregon, December 28, 1978.
2. Diehl A (1990). The effectiveness of aeronautical decision making.
3. FAA (1990). US Department of Transportation Advisory Circular - A series of Aeronautical decision making training manuals.
4. FAA (1990). US Department of Transportation Advisory Circular – Aeronautical Decision Making.

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