Definition
Legally binding notices issued by the FAA when an unsafe condition is found to exist in an aircraft, engine, propeller, or appliance. They specify the inspections, repairs, modifications, or operating limitations required to correct the condition, and compliance is mandatory for the aircraft to remain airworthy.
Plain English
Official FAA orders that tell owners and operators they must fix or check something on their aircraft because a safety problem has been identified. Until the work is done as required, the aircraft is not legal to fly.
Context Anchor
Pilots most often encounter Airworthiness Directives in aircraft maintenance records, during aircraft ownership, rental checkout, annual inspections, and preflight questions about whether an airplane is legal to fly.
Derivation
Airworthiness' comes from 'air' plus 'worthy' (Old English 'weorth' meaning 'having value or fitness'), so literally 'fit to fly.' A 'directive' is an authoritative instruction that must be followed. Together: a binding instruction needed to keep the aircraft fit to fly.
Why Pilots Care
Compliance is required to maintain a valid airworthiness certificate; ignoring an AD can ground the aircraft and create serious safety or legal liability.
Analogy
An Airworthiness Directive is similar to a mandatory safety recall on a car, but for aircraft it carries FAA legal force and directly affects whether the aircraft may be flown.
Intuition Check
Do not read “directive” as friendly advice or a suggestion. In this FAA use, an Airworthiness Directive is mandatory when it applies.
Example Sentence 1
Before the flight, the pilot reviewed the maintenance logs to confirm that all applicable Airworthiness Directives had been complied with.
Example Sentence 2
During the preflight, the owner verified that the most recent Airworthiness Directive for the propeller had been complied with on schedule.