Definition
A legally enforceable rule issued by the FAA when an unsafe condition is found to exist in an aircraft, engine, propeller, or appliance, and that condition is likely to exist or develop in other items of the same type design. Compliance with applicable Airworthiness Directives is mandatory before the aircraft may be flown.
Plain English
An official FAA order that tells owners and operators they must fix a known safety problem on a specific type of aircraft or part. The aircraft is not legal to fly until the required action is done.
Context Anchor
You will see ADs during aircraft ownership, maintenance planning, preflight document checks, and discussions about whether an aircraft is legal and safe to fly.
Derivation
"Airworthy" combines "air" with "worthy," meaning fit or suitable for flight. A "directive" is an authoritative instruction. Together: an order that brings an aircraft back to a fit-to-fly condition.
Why Pilots Care
Compliance is legally required; failure to follow an AD can ground the aircraft and result in enforcement action.
Intuition Check
Do not read directive as friendly advice here. An AD is a mandatory FAA requirement, not a recommendation.
Example Sentence 1
Before the flight, the pilot reviewed the maintenance records to confirm that all applicable Airworthiness Directives had been complied with.
Example Sentence 2
The owner scheduled the required inspection to comply with the AD on the elevator control system.