Airworthiness directives are legally enforceable FAA rules that correct an unsafe condition in an aircraft, engine, propeller or appliance. This guide explains how FAA airworthiness directives are issued, how AD applicability works by serial number and modification status, how one-time and recurring ADs differ, where an alternative method of compliance fits, and how an AI agent checks fleet applicability and drafts each determination for an engineer to sign off.
The FAA issues an AD when an unsafe condition exists in a product and is likely to exist or develop in other products of the same type design, under 14 CFR Part 39. Operating a product that fails to meet an applicable AD is a violation of the same part. The owner or operator carries the responsibility: 14 CFR 91.403(a) makes them primarily responsible for keeping the aircraft in an airworthy condition.
For a planner at an MRO shop or a records lead at a charter operator, the hard part is rarely reading one directive. It is answering the same question across a fleet: does this AD apply to this tail, this engine serial and this component, given everything already done to it? That question is where the reading time goes, and it is where AI earns its place.
What Airworthiness Directives Are and How the FAA Issues Them
ADs are published in full in the Federal Register as amendments to 14 CFR 39.13, so the regulation itself holds only the framework while each directive lives in its own Federal Register entry. Electronic copies are also available through the FAA’s Dynamic Regulatory System, as the FAA explains on its AD issuance and publication page.
The FAA uses three routes to issue an AD, described on its AD types page:
- NPRM followed by a final rule. The standard process. The FAA proposes the AD, takes public comments, then issues the final rule.
- Immediately adopted rule. Published in the Federal Register with a request for comments, for unsafe conditions that call for faster action than a full comment cycle.
- Emergency AD. Issued when an unsafe condition requires immediate action by an owner or operator. It applies to those who receive actual notice, and a final rule follows in the Federal Register.
FAA Airworthiness Directives: One-Time vs Recurring
Some ADs require a single action, such as replacing a part or incorporating a modification, and the record closes once the work is signed off. Others require repetitive or periodic inspection. FAA Advisory Circular 39-7D describes compliance times set as before further flight, or in flight hours, cycles or calendar time. One-time is industry shorthand for directives with no repeat interval, and the FAA treats it as a description rather than a formal category.
Recurring ADs drive most of the tracking effort. Each one carries a next-due value per aircraft or component, and that value moves every time the inspection is done, the part is swapped or a terminating action is incorporated. Under 14 CFR 91.417(a)(2), the operator keeps the current status of applicable ADs, including the method of compliance, and those records transfer with the aircraft when it is sold.
How AD Applicability Works: Serial Numbers and Modification Status
An AD’s applicability section names the products it covers. AC 39-7D notes that applicability can be limited by serial number, and that when an AD gives no serial numbers, all serial numbers are affected. Many ADs also scope by configuration: a directive may cover only units without a given modification, or only those with a particular part number installed.
Two rules in Part 39 make applicability harder than reading a list:
- Modified products stay in scope. Under 14 CFR 39.15, an AD applies even if an individual product has been changed by modifying, altering or repairing it. A modification takes a unit out of scope only when the AD itself says so.
- Incorporated bulletins become part of the AD. When an AD incorporates a service bulletin by reference, the bulletin’s instructions become part of the directive, and under 14 CFR 39.27 the AD’s requirements govern wherever the two conflict.
A complete applicability check needs four inputs: the AD text and every bulletin it incorporates, the aircraft or component serial number, the installed part numbers, and the modification and repair history. The answer is often conditional. For example, a directive might apply with compliance due at the next heavy check unless a specific bulletin revision is already incorporated.
Alternative Methods of Compliance (AMOCs)
An operator can propose a different way to meet an AD if it provides an acceptable level of safety, under 14 CFR 39.19. The request goes to the principal inspector and then to the manager named in the AD, and the alternative can be used only once that manager approves it. An approved AMOC belongs in the compliance record next to the directive it answers, because it changes the method of compliance and often the next-due calculation as well.
AD vs SB vs SIL: How the Documents Differ
Airworthiness directives sit alongside several other documents that technicians and planners read every week. The table sets out who issues each one, whether it is mandatory, and how an AI system treats it.
| Document | Issued by | Mandatory? | What it does | How AI handles it |
|---|---|---|---|---|
| Airworthiness directive (AD) | FAA, under 14 CFR Part 39 | Yes, a legally enforceable rule | Requires action to correct an unsafe condition | Parses applicability and compliance times, drafts a status per serial number |
| Service bulletin (SB) | Manufacturer | Advisory for Part 91 operators unless an AD or other rule requires it | Describes an inspection, modification or repair | Reads effectivity, links bulletins that ADs incorporate by reference |
| Service information letter (SIL) | Manufacturer | Informational | Shares service experience, clarifications and tips | Indexed for search next to the manuals |
| Special airworthiness information bulletin (SAIB) | FAA | Non-regulatory | Alerts, educates and recommends on an issue that falls below the AD threshold | Flagged for engineering review by fleet type |
The SB row follows a 2015 FAA Chief Counsel interpretation, and the SAIB row follows the FAA’s SAIB page. Operators under Parts 121 and 135 should also check how their own maintenance program treats bulletins.
How AI Checks Fleet Applicability for Airworthiness Directives
An AI agent built for AD work handles the reading and cross-referencing, and an engineer makes the call. A typical workflow runs in five steps:
- Ingest the directive. The agent pulls the new or revised AD with every bulletin it incorporates, then extracts the applicability statement, compliance times and any terminating actions.
- Match the fleet. It queries your maintenance tracking system for each candidate aircraft, engine or component by model, serial number and installed part numbers.
- Check modification status. It searches work orders, logbook entries and incorporated bulletins for modifications that change applicability or count as a terminating action.
- Draft the determination. For each serial number it writes a draft status, such as applies, excluded, or applies with a condition, and cites the AD paragraph and the record entries it relied on.
- Route for sign-off. The draft goes to the responsible engineer, who accepts, edits or rejects it. The compliance record changes only after a person signs.
The value sits in the citations. An engineer reviewing a draft sees the applicability paragraph next to the work order that shows a modification was incorporated, so the review becomes a check of evidence instead of a fresh search. Retrieval over your own documents keeps every answer tied to a source, and the agent’s reasoning is logged so auditors can follow how each determination was reached.
What an AD Compliance Record Holds
Every determination ends up in the AD status record that 14 CFR 91.417(a)(2) requires. A complete entry for each directive and each affected serial number usually holds:
- The AD number and revision date, plus any earlier AD it supersedes.
- The applicability determination and the evidence behind it, such as a serial number range or an incorporated modification.
- The method of compliance, including any approved AMOC.
- The date, hours and cycles at compliance, and for recurring ADs the hours, cycles or date when the next action is due.
- The signature and certificate number of the person approving the work, as 91.417(a)(1) requires for maintenance records.
These records move with the aircraft at sale or lease return, where the buyer’s team reviews them line by line. An entry that cites its evidence gives that reviewer the same trail the engineer used, and it gives your own auditors a quicker path through the file.
Where an Agent Fits With AD Compliance Software
AD compliance software and maintenance tracking systems store AD lists, compliance status and next-due dates, and many operators subscribe to AD research services that flag new directives for their fleet types. That system of record stays in place. An agent adds a reading and drafting layer on top of it: it reads the directive text and your records together, writes the reasoning, and passes back only what the engineer approves.
Our aircraft maintenance software copilot runs this workflow with a read-only connection to your tracking system, so airworthiness directive software you already pay for keeps doing its job while the agent handles the cross-referencing.
Keeping AD Data and Records Private
ADs are public documents, and the records they are checked against are private. Tail histories, customer aircraft data and OEM-licensed manuals all carry confidentiality or licence terms, so the agent, its index and its logs run on servers inside your network or in your own cloud tenant. Many shops start AD work as one part of a wider AI in aviation program that also covers manual search and records digitization.
Getting Started With AI for Airworthiness Directives
A pilot on one fleet type gives you evidence before you scale. Export the AD list and compliance records for that fleet, then run the agent in shadow mode on directives your engineers have already dispositioned. Compare each draft with the signed determination, review every disagreement with the engineer who made the call, and set the agreement level you need before the agent drafts live determinations. Once the shadow results meet that bar, add the next fleet type.
Checking AD applicability by hand across a mixed fleet? NeuralChainAI builds private aircraft maintenance software with an AD agent that drafts each determination for your engineer to sign. Book a strategy session to scope a pilot on one fleet type.
