Definitions of key terms

The NTSB, FAA, and the airline industry use definitions for accidents and incidents that are described below. While the FAA, NTSB, and airline industry are focused on accidents, takes a broader approach that includes events that are not due to accidental causes, and that approach is reflected in the definitions used on the site.

FAA and NTSB definitions

Both the NTSB and FAA use terminology that is defined in US federal statutes, specifically in the Code of Federal Regulations (CFR), Title 49, section 830.2. These terms may change as the CFR is updated, so refer to the most current CFR for the latest version of these terms. Below are a summary of the most important terms:

Aircraft accident: An occurrence associated with the operation of an aircraft which takes place between the time any person boards the aircraft with the intention of flight and all such persons have disembarked, and in which any person (either inside or outside the aircraft) suffers death or serious injury, or in which the aircraft receives substantial damage.

Aircraft incident: An occurrence other than an accident that affects or could affect the safety of operations.

Fatal injury: Any injury which results in death within 30 days of the accident.

Serious injury: Any injury which requires hospitalization for more than 48 hours, commencing within seven days from the date of the injury. Also includes other injuries, including fractures of any bones (except simple fractures of the toes, fingers, or nose), severe bleeding, internal organ injuries, and severe burns.

Substantial damage: Damage or failure which adversely affects the structural strength, performance, or flight characteristics of the aircraft, and which would normally require major repair or replacement of the affected component.

Industry definitions

The airline industry uses additional terminology to describe aviation events, particularly accidents. Boeing is one of the airline industry's leaders when it comes to safety, and the following terms are taken from their publication Statistical Summary of Commercial Jet Airplane Accidents.

Accident rates: In general, this expression is a measure of accidents per million departures.

Hull Loss: A situation where the airplane is totally destroyed or damaged and not repaired. Hull loss also includes, but is not limited to, events in which the airplane is missing, the search for wreckage has been terminated without the airplane being located, or the airplane is completely inaccessible. definitions

The FAA, NTSB, and airline industry focus on accidents, and exclude events that involve the deliberate action of one or more people. Examples include hijacking, sabotage, and military action. Also, explicitly defines some concepts that are not defined at all, or that are not defined in a consistent manner by the FAA, NTSB, and airline industry. Key definitions include the following:

Deliberate event: A fatal event or significant event that was caused by the deliberate or planned actions of one or more people. This would include events such as hijacking, sabotage, or military action. A crew member or passenger involved in a deliberate event would be subtracted from the number of crew members or passengers on that aircraft, and if killed would not be included in the number of deaths associated with the event.

Ditching: An event where the flight crew intentionally lands an aircraft in some body of water such as a lake, a river, or the open ocean. In addition, the event would have to meet the following conditions or criteria:

  • The water landing has to be intentional. Accidental or unintentional landings or excursions onto water are excluded, such as runway overruns or controlled flight into water.
  • Uncontrolled impacts with water are excluded.
  • The body of water must be deep enough so that if the aircraft sinks, some or all of the occupants would have to evacuate the aircraft cabin to avoid drowning.

Fatal event: Any circumstance involving a particular aircraft where one or more passengers die during a flight from causes that are directly related to a civilian airline flight. The fatal event may be due to an accident or due to a deliberate act by another passenger, a crew member, or by one or more persons not on the aircraft.

These events include sabotage, hijacking, or military action and exclude cases where the only passenger deaths were to hijackers, saboteurs, or stowaways. If there are two or more aircraft involved in the event, and there are passenger fatalities from more than one aircraft, then each aircraft with a passenger fatality would constitute a separate fatal event.

The flight can be either scheduled or unscheduled, but it must be one where members of the general public are allowed to be passengers. Also, the aircraft model must be of a size and type that is typically used in airline service.

Fatal event rate: The number of numbered events for a particular category of aircraft, for example a particular aircraft model, divided by the number of flights made by that aircraft category.

Fatality: A death of any person inside or outside of an aircraft, spacecraft, or other aerospace vehicle that occurs during a flight operation or other operation involving that vehicle. In the case of a significant event, a fatality could also include situations that do not involve an aerospace vehicle. All events with one or more fatalities would be considered a fatal event, except where the only deaths were to stowaways, hijackers, or saboteurs.

Full loss equivalent (FLE): The proportion of passengers killed in a numbered event. For example, 50 out of 100 passengers killed on a flight results in an FLE of 0.50, 1 of 100 would result in an FLE of 0.01.

Full loss equivalent (FLE) rate: The FLE rate for a particular aircraft model would be found by dividing the sum of the individual FLE values by the number of flights made by that aircraft model.

Numbered event: This is either a fatal event or a significant event that is included in a risk-based statistic in a particular context.

On the site, the context is related to the subject of a particular page, and the nature of the relationship is typically described on that page. For example, pages about particular aircraft models would have as a numbered event only fatal events where one or more passengers were killed.

The context may be different on other types of pages. For example, on pages summarizing fatal and significant events for a particular year, all events resulting in passenger deaths on jet airliners would be numbered events. Also counted would all events involving passenger deaths on turboprop-driven aircraft models with a capacity of 10 or more passenger seats, which are certified for passenger service in the US.

This requirement for turboprop-driven aircraft is based on FAA requirements that airlines using passenger aircraft with 10 or more passenger seats operate under a similar set of regulations. As a result of this requirement, non-turboprop aircraft and turboprop aircraft models that are not certified for passenger service in the US would not be numbered events. Aircraft certified in the US are typically also certified to operate in Canada, North America, Japan, Australia, and the European Community, countries which collectively account for a majority of the world's airline flights.

Passenger: A person on board of an aircraft who is not a crew member, saboteur, hijacker, or stowaway.

Passenger flight: A scheduled or unscheduled flight on an aircraft that is operated as an airline flight where the general public has an opportunity to be a passenger.

Risk: A combination of a specific hazard and the likelihood that the hazard occurs (probability)x(hazard) = risk. That likelihood may be expressed as a rate or a probability. For example the risk of an aircraft accident (hazard) can be expressed as one accident per million flights (likelihood).

Risk assessment: The process of analyzing potential losses from a given hazard using a combination of known information about the situation, knowledge about the relevant underlying processes, and judgments about aspects of the situation that are not well understood.

Risk management: The process of combining a risk assessment with decisions on how to address that risk, and doing so in ways that consider the technical and social aspects of the risk assessment.

Significant event: An event that is of interest to airline passengers and the aviation safety community, but that in the context of where it appears on the site, is not a numbered event. Characteristics of significant events include, but are not limited to, the following:

  • The event received significant attention from the news media.
  • There was a fatality associated with the event.
  • The event had either caused significant changes to airline safety or security policy, or has the potential to lead to future changes.
  • The event was associated with one or more hazards that may lead to a future fatal event.
  • The event was an accident or deliberate act that resulted in the deaths of people who were not occupants of an aircraft.
  • The event involved a prominent political figure or celebrity.
  • The event was a non-fatal aerospace related event that is, or was, the subject of an official civil or military accident investigation.

Related resources
Risk assessment basics method for computing fatal event rates

Definitions of key terms -- Revised: 2 July 2017