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Accidents: Absent defenses


In recent years a revolution has occurred in the way we look at human error in aircraft accidents. Many organizations (military, civilian, and medical for example) have adopted a version of the human factors analysis classification system (HFACS), originally developed by Douglas A. Wiegmann and Scott A. Shappell.

This system of error classification is somewhat unique in that it is a comprehensive analysis tool that considers the organizational, physiological, behavioral, ergonomic, psychosocial, and cognitive perspectives of human error together.

Generally these perspectives are considered somewhat separately and so individually lack analytical power to explain why human error has occurred. And while each perspective has certain benefits, none consider all the aspects of human error completely.

HFACS strives to fill this need by looking at all the various perspectives using a single human error analysis tool.

The model is elegant but also simple to understand, which facilitates its use in deciphering the often ambiguous nature of human error.

A four-tiered hierarchical structure looks at the organizational factors, supervisory issues, preconditions for unsafe acts, and the unsafe acts that frequently precede the accident.

It is sometimes the case that the organization is ultimately at fault for an accident but it is often difficult to directly link failure at the administrative level to failure in the cockpit.

The supervisory level of an organization, generally associated with the management of day-to-day operations is also suspect in many accident cases. Failure to provide adequate supervision can easily lead to unsafe operations. But these two levels of the hierarchy assume the pilot(s) operate within an organization and as general aviation pilots we tend not to fall under such jurisdictions.

It is at the level of preconditions for unsafe acts and the unsafe acts themselves that we’ll focus on in this, and next month’s articles.

Preconditions for unsafe acts

Although the pilot may commit an unsafe act with no precondition, in many cases, these preconditions represent the focal point for potential accidents.

By "precondition" Wiegmann and Shappell refer to environmental and personnel factors that impact the condition of the operator (pilot).

The environment quite obviously presents many potential traps for the pilot. Specifically, the physical environment offers bad weather, poor lightning, noise, heat, pollutants, etc., that all effect the ability of the pilot to act correctly.

The emotional reaction to bad weather encounters notwithstanding, the physical environment is frequently distracting to the pilot. In addition, the technological environment sometimes offers equipment and controls that are not nearly as intuitive as they should be - automation complexity, poor procedure design with poor manuals or checklists, and complex avionics interfaces and displays.

For example, if you’ve ever used a GPS unit and found it difficult to set up or use correctly, then you had a precondition for an unsafe act lurking in the shadows.

Personnel factors can also impact the condition of the pilot through failed CRM or personal readiness for the mission at hand. Of course single pilot flying tends not to refer to CRM but the failed interaction with ATC certainly qualifies under this overarching concept of personnel interaction.

More importantly perhaps is our own readiness for flight. Common violations of personal readiness include inadequate rest prior to flight, bottle-to-throttle rule infractions, and self-medicating.

Also, we see poor judgment being exercised frequently. Poor dietary practices and/or physical exertion lead to physiological problems that can easily impact the safety of flight.

So both environmental factors and personnel factors influence the condition of the pilot. More specifically, as a result of either, or both, the pilot can experience adverse mental states, adverse physiological states, or even physical or mental limitations.

Adverse mental states more commonly appear as a loss of situational awareness, complacency, overconfidence, mental fatigue, distractions, etc. It is clear that personal readiness has a direct impact on mental preparedness for a flight.

Anything from a bad night sleep, medication, to having a fight with the spouse, can easily create one of these adverse mental states.

Medicine is also often to blame for adverse physiological states such as spatial disorientation, hypoxia, and visual illusions. But of course a medical illness all by itself is quite capable of rendering a pilot physiologically unfit to fly.

Physical and mental limitations are probably less of a problem for airline pilots and more of a problem in the general aviation world. These are things like eyesight limitations, lack of medical currency or qualifications, physical capabilities that are incompatible with the mission, and intelligence or aptitude incompatibilities.

As to the later, people ask me all the time how they could possibly be a pilot and not be intelligent enough or not have the aptitude required to fly.

My reply is a simple one; sometimes pilots take on missions that are beyond their skill and knowledge level. The accident briefs are full of fine examples of pilots who thought they had the "right stuff."

Physical limitations are also somewhat rare, but occur often enough to warrant caution. Pilots flying without proper eyesight correction is frequently cited as a problem, and other more serious physical deficiencies are not unheard of.

So we see that there is more to an accident than the simple act of having one. Something leads to that accident and it is frequently a "precondition" of a bad environmental factor or personnel factor that precipitates the adverse condition of the pilot.

This is not always the case, but often times. On occasion, the pilot just does something stupid with no real precondition for it, and it is these unsafe acts that pilots commit that we will delve into next month.

This month’s Pilot Primer is written by Donald Anders Talleur, an Assistant Chief Flight Instructor at the University of Illinois, Institute of Aviation. He holds a joint appointment with the Professional Pilot Division and Human Factors Division. He has been flying since 1984 and in addition to flight instructing since 1990, has worked on numerous research contracts for the FAA, Air Force, Navy, NASA, and Army. He has authored or co-authored over 180 aviation related papers and articles and has an M.S. degree in Engineering Psychology, specializing in Aviation Human Factors.