In an attempt to find a more timely indication of the effects of programs in improving safety or the impact of developments that might lead to a degradation of safety, analysts have turned to other events that they hope might elucidate changes in aviation safety. One approach has been to monitor and study incidents—events involving damage to an aircraft and/or injury, but in which the levels of damage or injury do not meet the NTSB thresholds that define an accident6—in the hope of more quickly detecting changes that could potentially affect safety. For example, the FAA Accident/Incident Data System (AIDS) contains reports of collisions between aircraft and birds while flights are on approach to or departure from an airport. Most of these collisions have not resulted in sufficient aircraft damage to be considered an accident by the NTSB. Nonetheless, the rate at which such collisions have occurred can be valuable safety information that might reveal an increase in the presence of birds around airports and suggest potential value in establishing programs to deter birds from nesting in areas adjacent to airports. One important problem, however, is that none of these other indices or events that analysts have turned to have been proven to be precursors to accidents or indicators of a pending increase in fatality rates or fatal accident rates. Even changes in the rates of nonfatal accidents or incidents have not been shown to be predictive of or associated with changes in the rates of fatal accidents. Thus, a link between any of these other indicators and the safety of the aviation system is at best uncertain.

Another complicating factor in understanding and improving aviation safety is that accidents rarely have a single cause.7 Rather, they are typically the result of a sequence of events involving several malfunctions and/or mistakes. Consider a situation in which an event initiates a sequence of other events that result in damage to an aircraft and/or injury. The same event might occur in another flight but not lead to an accident or injury because something else was done to interrupt the sequence of events. By studying the circumstances and learning how the sequence of events was interrupted, it might be possible to incorporate such information into training or aircraft design and to reduce rates of future accidents. Consider, for example, a flight in which an engine fails during takeoff. With a modern passenger jet aircraft, an engine failure during takeoff should not result in an accident if the pilot takes the correct actions quickly. However, an engine failure places considerable pressure on the pilot, who may not react quickly enough to assess the situation and take the correct action. If one could identify, study, and learn from flights during which actions were taken in time to prevent an accident, it might be possible to improve pilot training so as to reduce the chances of such failures resulting in accidents in the future.


The accident and incident data available from NTSB and FAA are not the only sources of safety data. Two other sources on reports of potentially unsafe events are the Aviation Safety Reporting System (ASRS) and airlines’ Aviation Safety Action Programs (ASAPs). ASRS receives, processes, and analyzes voluntarily submitted incident reports from pilots, air traffic controllers, dispatchers, flight attendants, maintenance technicians, and others. ASRS grew out of the FAA’s Aviation Safety Reporting Program (ASRP), started on April 30, 1975. The FAA determined that the effectiveness of ASRP would be enhanced if the receipt, processing, and analysis of raw data were done by NASA—an independent third party with no enforcement responsibility—rather than by the FAA. This practice would ensure the anonymity of all parties involved, including the reporter, and would increase the flow of information. Accordingly, NASA designed and administered ASRS through a Memorandum of Agreement executed by the FAA and NASA on August 15, 1975, and subsequently renewed periodically.8 In 1996, ASAPs were introduced in the flight domain with the hope of encouraging pilots to disclose their errors and, more importantly, the factors


Following is the definition of incident from International Civil Aviation Organization (ICAO) Annex 13 and FAA Order 8020.11b: “an occurrence other than an accident associated with the operation of an aircraft, which affects or could affect the safety of operations.” For more information on thresholds between an accident and an incident, see National Transportation Safety Board (NTSB), Form 6120.1 Pilot/ Operator Aircraft Accident/Incident Report, NTSB, October 2006, available at, accessed June 11, 2009.


James Reason, Human Error, Cambridge University Press, Cambridge, United Kingdom, 1990.


See FAA, Advisory Circular 00-46D, Washington, D.C., February 26, 1997, available at$FILE/AC00-46D.pdf, accessed July 15, 2009.

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