De International Civil Aviation Organisation classificeert voorvallen afhankelijk van de ernst, in een vijftal categorieën.

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;

Major Incident: an incident associated with the operation of an aircraft, in which safety of aircraft may have been compromised, having led to a near collision between aircraft, with ground or obstacles (i.e., safety margins not respected which is not the result of an ATC instruction);

Significant Incident: an incident involving circumstances indicating that an accident, a serious or major incident could have occurred, if the risk had not been managed within safety margins, or if another aircraft had been in the vicinity;

No safety effect: an incident which has no safety significance;

Not determined: insufficient information was available to determine the risk involved or inconclusive or conflicting evidence precluded such determination.