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.
If a certified aircraft has outstanding airworthiness directives that have not been complied with, the aircraft is not considered airworthy. Thus, it is mandatory for an aircraft operator to comply with an AD.
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 of 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 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.
ADs are mandatory in most jurisdictions and often contain dates or aircraft flying hours by which compliance must be completed.
ADs may be divided into two categories:
- Those of an emergency nature requiring immediate compliance prior to further flight, and
- Those of a less urgent nature requiring compliance within a specified period of time.
ADs are issued by most civil aviation regulatory authorities, including:
The FAA issues ADs by three different processes:
- Standard AD process: Notice of Proposed Rulemaking (NPRM), followed by a Final Rule
- Final Rule and Request for Comments
- Emergency airworthiness directives - issued without time for comment. This is only used issued "when an unsafe condition exists that requires immediate action by an owner/operator...to rapidly correct an urgent safety of flight situation."
- Transport Canada (October 2008). "Aeronautical Information Manual, LRA - 2.0 Aircraft Airworthiness, Airworthiness Directives". Archived from the original on 2011-04-17. Retrieved 2008-11-03.
- Transport Canada (January 2008). "Canadian Aviation Regulation 605.84 Aircraft Maintenance - General". Archived from the original on 7 December 2008. Retrieved 2008-11-03.
- Transport Canada (January 2008). "Canadian Aviation Regulation Standard 593.02 Airwothiness Directives". Archived from the original on 2013-05-18. Retrieved 2008-11-03.
- Pilot's Handbook of Aeronautical Knowledge. US Department of Transportations, Federal Aviation Administration. 2016. pp. 9–12.
- Federal Aviation Administration (October 2009). "Types of Airworthiness Directives". Archived from the original on 16 October 2009. Retrieved 2009-10-04.