General (ICAO)

ICAO Annex 13 — Aircraft Accident and Incident Investigation, Chapter 1 (Definitions) defines key investigation terms:

Accident — An occurrence associated with the operation of an aircraft which, in the case of a manned aircraft, takes place between the time any person boards the aircraft with the intention of flight until such time as all such persons have disembarked, and in which:

a) a person is fatally or seriously injured as a result of: being in the aircraft, or direct contact with any part of the aircraft (including detached parts), or direct exposure to jet blast. Excluding: natural causes, self-inflicted or inflicted by others, and injuries to stowaways outside normal passenger/crew areas, or
b) the aircraft sustains damage or structural failure that adversely affects structural strength, performance or flight characteristics and normally requires major repair or replacement of the affected component. Excluding: engine failure or damage limited to a single engine (including its cowling or accessories), damage to propellers, wing tips, antennas, tyres, brakes, fairings, small dents or holes in the skin, or
c) the aircraft is missing or completely inaccessible.

Fatal injury — Injury resulting in death within 30 days of the accident.

Serious injury — Injury in which a person:

is hospitalised for more than 48 h within 7 days of the injury, or
has fractures of any bone (except fingers, toes, nose), or
has extensive lacerations causing severe haemorrhage, nerve/muscle/tendon damage, or
has internal organ injury, or
has 2nd or 3rd degree burns or burns over >5% body surface, or
has been exposed to infectious substances or injurious radiation.

Serious incident — An incident involving circumstances indicating that there was a high probability of an accident. Examples in Annex 13 Attachment C: near collision, loss of control, collision during taxi/take-off, engine fire, CFIT narrowly avoided, severe structural damage, emergency landing with or without success, etc.

Incident — An occurrence (other than an accident) associated with the operation of an aircraft, which affects or could affect the safety of operation.

Investigation — A process conducted for the purpose of accident prevention, comprising the gathering and analysis of information, drawing of conclusions including the determination of cause(s) and/or contributing factors and, when appropriate, the making of safety recommendations.

Europe (EASA / EU)

The ICAO Annex 13 definitions are adopted into EU law verbatim via Regulation (EU) 996/2010 on the investigation and prevention of accidents and incidents in civil aviation, Article 2 (Definitions).

Germany (national)

Direct application of EU 996/2010. The competent investigation authority is the Bundesstelle für Flugunfalluntersuchung (BFU) in Braunschweig (see "Investigation objective" lesson). Definitions adopted unchanged via the Flugunfall-Untersuchungs-Gesetz (FlUUG).