The short answer
An Airworthiness Directive (AD) is a legally enforceable rule issued by the FAA to correct an unsafe condition found in an aircraft, engine, propeller, or appliance. Compliance is mandatory: each AD specifies which serial numbers or models it applies to, what must be done, and by when.
How ADs work
ADs are issued under 14 CFR Part 39 when the FAA finds an unsafe condition likely to exist in other products of the same design. Each AD defines its applicability (models, serial ranges, configurations), the required action (inspection, modification, replacement, or operating limitation), and a compliance time — hours, cycles, calendar date, or before further flight.
Some ADs are one-time; many are recurring (for example, an inspection every 100 hours until a terminating action is performed). Owners are responsible for maintaining a record of AD compliance status, including the method of compliance and the date and time at which each was accomplished.
Tracking compliance
AD status is checked at every annual inspection, but the list changes year-round as the FAA issues new directives. Keeping a current AD compliance record — what applies, what's been done, and when recurring items come due — is one of the core disciplines of maintenance recordkeeping.
Related terms and reading
Keep every hour and inspection straight
Maggneto tracks engine times, inspections, and ADs from your actual logbooks — so terms like these become numbers you can act on. Browse the full maintenance glossary.
Frequently asked questions
Are Airworthiness Directives mandatory?
Yes. ADs are regulations issued under 14 CFR Part 39, and no person may operate a product to which an AD applies except in accordance with that AD's requirements.
What is the difference between an AD and a service bulletin?
A service bulletin is issued by the manufacturer and is generally advisory for Part 91 operators; an AD is issued by the FAA and is legally binding. ADs frequently reference or mandate a manufacturer's service bulletin, which is what makes that bulletin's actions required.