An airworthiness directive (commonly abbreviated as AD) is a notification to owners and operators of certified aircraft that a known safety deficiency with a particular model of aircraft, engine, avionics or other system exists and must be corrected. Compliance with Airworthiness Directives is mandatory.
ADs usually result from service difficulty reporting by operators or from the results of aircraft accident investigations. They are issued either by the national civil aviation authority of the country of aircraft manufacture or of aircraft registration. When ADs are issued by the country of registration they are almost always coordinated with the civil aviation authority of the country of manufacture to ensure that conflicting ADs are not issued.
In detail, the purpose an AD is to notify aircraft owners:
- that the aircraft may have an unsafe condition, or
- that the aircraft may not be in conformity with its basis of certification or of other conditions that affect the aircraft's airworthiness, or
- that there are mandatory actions that must be carried out within the stated compliance time to ensure continued safe operation, or
- that, in some urgent cases, the aircraft must not be flown until a corrective action plan is designed and carried out