Definition
Airworthiness Directives (ADs) are legally enforceable regulations issued by the FAA to correct an unsafe condition that exists in an aircraft, engine, propeller, or appliance. Compliance with applicable ADs is mandatory, and the work performed must be recorded in the aircraft's maintenance records.
Plain English
An AD is an official FAA order telling owners and mechanics that something on the aircraft must be checked, fixed, or modified because a safety problem has been identified. You are not allowed to fly the aircraft legally unless the required action has been done.
Context Anchor
Pilots encounter ADs when checking aircraft maintenance records, confirming an aircraft is airworthy, or teaching students how to verify that an aircraft is legal to fly.
Derivation
From 'airworthy' (fit and safe to fly) and 'directive' (an authoritative instruction). Together it means an authoritative instruction required to keep the aircraft safe to fly.
Why Pilots Care
Compliance is mandatory to keep the aircraft legally airworthy; failure to address an AD can ground the airplane and create liability.
Intuition Check
ADs are not suggestions or general advice. They are mandatory safety requirements when they apply to the aircraft or part you plan to use.
Example Sentence 1
Before the flight, the mechanic confirmed that all applicable ADs had been complied with and signed off in the logbook.
Example Sentence 2
Before a cross-country flight the instructor checked for any new ADs that applied to the training fleet.