Important Definitions taken from ICAO Annex 13.
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 until such time as all such persons have disembarked, in which:
a) A person is fatally or seriously injured as a result of:
1. Being in the aircraft, or
2. Direct contact with any part of the aircraft, including parts which have become detached from the
aircraft, or — direct exposure to jet blast,
Except when the injuries are from natural causes, self-inflicted or inflicted by other persons, or when the injuries are to stowaways hiding outside the areas normally available to the passengers and crew; or
b) The aircraft sustains damage or structural failure which:
Adversely affects the structural strength, performance or flight characteristics of the aircraft, and — would normally require major repair or replacement of the affected component,
Except for engine failure or damage, when the damage is limited to the engine, its cowlings or accessories; or for damage limited to propellers, wing tips, antennas, tires, brakes, fairings, small dents or puncture holes in the aircraft skin; or
c) The aircraft is missing or is completely inaccessible.
Note 1.For statistical uniformity only, an injury resulting in death within thirty days (30 days) of the date of the accident is classified as a fatal injury by ICAO.
Note 2. An aircraft is considered to be missing when the official search has been terminated and the wreckage has not been located.
Serious incident. An incident involving circumstances indicating that an accident nearly occurred.
Note. The difference between an accident and a serious incident lies only in the result.
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 which includes the gathering and analysis of information, the drawing of conclusions, including the determination of causes and, when appropriate, the making of safety recommendations.