14 CFR Part 39 — Airworthiness Directives: Compliance and Documentation

What Is an Airworthiness Directive?

An Airworthiness Directive (AD) is a legally enforceable regulation issued by the FAA under the authority of 14 CFR Part 39. When the FAA determines that an unsafe condition exists in an aircraft, engine, propeller, or appliance — and that the condition is likely to exist or develop in other products of the same design — it issues an AD to require corrective action. Compliance with an applicable AD is not optional. Operating an aircraft out of AD compliance makes the aircraft unairworthy, and a certificated mechanic who knowingly approves such an aircraft for return to service may face certificate action.

ADs are published in two forms: Final Rules (the binding regulation) and, when time is critical, Emergency ADs that take effect immediately. Many ADs also go through a Notice of Proposed Rulemaking (NPRM) stage, giving the public an opportunity to comment before the rule is finalized.

Structure of 14 CFR Part 39

Part 39 is short. It establishes the FAA's authority to issue ADs, defines what compliance means, and states that the person operating the aircraft is responsible for ensuring all applicable ADs are complied with. The actual technical requirements for each unsafe condition appear in the individual AD documents themselves, not in the body of Part 39.

Each individual AD contains these standard sections:

• Docket Number and AD Number — uniquely identifies the document (e.g., 2023-XX-XX)
• Applicability — the specific makes, models, and sometimes serial number ranges affected
• Unsafe Condition — a plain-language description of the hazard and its cause
• Compliance — the time limit within which the action must be completed (for example, within a certain number of flight hours, calendar days, or cycles after the effective date)
• Actions Required — the specific inspection, modification, replacement, or operational limitation required
• Alternative Methods of Compliance (AMOC) — the procedure for requesting FAA approval to use a different but equally safe method
• Related Information — references to manufacturer service bulletins or other documents

Finding Applicable ADs

The FAA's Regulatory and Guidance Library at rgl.faa.gov is the official, free, publicly accessible database for ADs. You can search by aircraft make, model, and series, or by engine or propeller type. The FAA AD Search function returns a list of all ADs that have ever applied to that product type. It is your responsibility to then read each one and determine whether the specific serial number in front of you falls within the applicability statement.

A best practice during a compliance check is to print or save a copy of every applicable AD, note the compliance time required, and then compare that to the aircraft's logbooks and maintenance records to determine whether each AD has already been accomplished and whether any recurrent actions are coming due.

Determining Compliance Status

After identifying all applicable ADs, you must check the aircraft's maintenance records — typically the airframe, engine, and propeller logbooks — to verify compliance. Look for a logbook entry that references the specific AD number and revision. If no entry exists, the AD may not have been accomplished, and the aircraft may be unairworthy.

For one-time ADs, a single completed entry closes out the requirement permanently, assuming the aircraft's total time at compliance was within the required window.

For recurrent ADs (those requiring repeated action at specified intervals), you must calculate the next due time by adding the recurrence interval to the total time or date at which the last action was performed.

Writing the Logbook Entry

A compliant AD logbook entry must contain, at minimum:

1. The AD number and revision letter (e.g., AD 2022-14-10, Amendment 39-XXXXX)

2. The method of compliance (inspection, replacement, modification, or reference to a specific service bulletin)

3. The date the work was performed

4. The aircraft or component total time at the time of compliance

5. The next due time or date (for recurrent ADs)

6. The signature and certificate number of the certificated mechanic or repairman performing or supervising the work

Incomplete entries are a common finding during FAA inspections. An entry that omits the AD revision, the total time, or the mechanic's certificate number does not satisfy the regulatory requirement and could be treated as if no compliance was recorded.

Safety Considerations

Many ADs involve work on fuel systems, flight control systems, or rotating components where improper technique creates immediate hazards. Before performing any AD-required maintenance:

• Review all applicable safety precautions in the referenced service bulletin or manufacturer instructions.
• Apply lockout/tagout procedures any time you are working on systems that could energize unexpectedly — electrical, hydraulic, or pneumatic.
• Use the correct PPE for the task: safety glasses for inspections involving debris or fluids, gloves when handling solvents or sharp structural components.
• Never return an aircraft to service until all required inspections, measurements, and sign-offs are complete and the logbook entry is written and signed.

Remember: an aircraft with an open, uncorrected AD is legally unairworthy. No maintenance release or return-to-service approval may be issued until compliance is achieved or a valid AMOC is in effect.