Which Airworthiness Directives Apply to Your Aircraft — and How Applicability Is Really Decided

You already get the free EASA and FAA alerts. A new Airworthiness Directive is published, an email lands, and — technically — you know about it. But knowing an AD exists is not the same as knowing whether it applies to your fleet. That second question is the one that grounds an aircraft or produces a finding in an audit, and it's the one no alert answers for you.

This article walks through how AD applicability is actually determined: what "applicable" means, the aircraft-level inputs that decide it, how an AD scopes itself down to specific tails, and the cross-authority trap that catches mixed EASA/FAA fleets. It's written for the CAMO team that has to turn a stream of directives into a defensible, per-aircraft answer.

The question that grounds an aircraft — or fails an audit

An Airworthiness Directive is a legally mandatory instruction from an airworthiness authority to correct an unsafe condition on a type, model, or appliance. When one is issued, the obligation isn't "read it" — it's to determine, for each aircraft you manage, whether the condition it addresses is present, and if so, to comply by the stated deadline and keep the evidence.

The determination is deceptively hard because it depends on the specific state of each aircraft, not just its type. Two aircraft of the same model can have different answers to the same AD — because of a different serial number, a different modification history, or a different engine variant. Get the determination wrong in the permissive direction and you have an undetected non-compliance flying. Get it wrong in the conservative direction and you've grounded or reworked an aircraft for nothing. Either way, the auditor will want to see how you decided.

"Applicable" is not the same as "an AD exists"

It helps to separate three things that alerts blur together:

• Published — the AD has been released by an authority. This is what the free email tells you.
• Applicable — the AD's conditions match a specific aircraft's actual configuration and state.
• Complied — the required action has been performed (or the aircraft is confirmed not to need it), with evidence.

The middle step is the product of continuing-airworthiness work. It's where type, serial, configuration, and directive language all have to line up. Alerts hand you "published"; audits ask about "applicable" and "complied." The gap between them is the job.

The inputs that decide applicability

To determine whether a given AD applies to a given aircraft, you're matching the directive's applicability statement against a handful of aircraft facts:

• Type certificate / TCDS. Every aircraft is certified under a type certificate, described by its Type Certificate Data Sheet (TCDS). Anchoring an aircraft to the correct TCDS and type designation is the foundation — because ADs are written against types, models, and the appliances installed on them. An aircraft anchored to the wrong type will inherit the wrong AD set.
• Model / variant. Within a type, ADs frequently target specific models or variants only.
• Serial number (MSN). Many ADs apply only to a range of serial numbers — typically the aircraft built before a fix was incorporated on the production line.
• Modification and configuration state. Whether a particular modification, service bulletin, or STC has been embodied — and which part numbers are actually installed — can put an aircraft inside or outside an AD's scope.
• Engine and propeller variant. Engines and propellers carry their own type certificates and their own ADs. The engine variant fitted to an airframe changes which powerplant ADs apply, independent of the airframe itself.

Miss or mis-record any of these and the applicable-AD list shifts. This is why a spreadsheet keyed only on "aircraft type" tends to over- or under-state applicability: the type is only the first of several inputs.

Effectivity: how an AD scopes itself down

Every AD contains an applicability (or effectivity) statement that narrows it from "this type" to "these specific aircraft." In practice that scoping is expressed as some combination of:

• a serial-number range (e.g., aircraft up to a certain MSN),
• installed part numbers (the AD applies only if a specific part or component is fitted),
• prior modification state (applies unless a particular mod or SB has been embodied, or applies only if it has),
• optional-equipment conditions (applies if a certain configuration is present),
• and sometimes operational conditions (flight-hour or cycle thresholds that bring an aircraft into scope).

Reading effectivity correctly is exact work, not fuzzy matching. "Close enough" is exactly how a fleet ends up with a directive on the wrong aircraft — or, worse, off an aircraft it belongs to. The right posture is deterministic: if the aircraft's state clearly matches, it's in; if it clearly doesn't, it's out; and if the data needed to decide is missing or ambiguous, that's an explicit "unknown to be resolved" — never a silent assumption in either direction.

The cross-authority question: is it the same directive twice?

Most fleets aren't single-authority. As soon as you operate across EASA and FAA — or manage aircraft whose State of Design differs from their State of Registry — you hit a second layer: the same underlying unsafe condition can be mandated by two authorities under two different AD numbers.

Typically one authority is the State of Design and issues the original AD; the other adopts it as mandatory continuing-airworthiness information (a "foreign AD" or MCAI). The comply-once principle means that satisfying the original generally satisfies the adopting authority's version — but only if you know the two are the same directive. If you don't link them, two failure modes appear:

• Double-counting — the same action tracked as two open items, inflating workload and confusing the record.
• Missed cross-jurisdiction AD — an aircraft on one register that's subject to a directive issued by the other authority, never picked up because you were only watching one source.

Deduplicating and cross-linking equivalent directives across authorities is therefore part of getting the applicable list right — not a nice-to-have.

Why alerts and spreadsheets leave the hard part to you

Free authority alerts are genuinely useful for one thing: telling you an AD was published. They don't know your fleet. They can't read effectivity against your serial numbers, your mod states, or your engine variants, and they can't reconcile an EASA number against its FAA twin. So every alert still resolves to the same manual task — open the directive, and check applicability by hand, tail by tail.

A spreadsheet helps you store the result, but it doesn't compute it, and it quietly rots: a mis-typed serial, an un-updated mod state, a superseded AD still marked open, a recurring inspection that silently came due again. The work — and the risk — stays with the person maintaining the sheet.

How Aviagent determines applicability

Aviagent takes the same published directives and does the applicability determination against your actual fleet. Each aircraft is resolved to its type and TCDS, its MSN, its configuration, and its engine variant. Every EASA, FAA, TCCA, and ANAC AD is then matched against that state — reading effectivity deterministically, deduplicating comply-once directives across regulators, and flagging exactly which aircraft and parts are affected, by when.

Two principles are deliberate. First, the matching is exact, not fuzzy — where the data needed to decide is missing, the result is an explicit "unknown" to be resolved, never a fabricated empty answer. Second, engineering judgement stays with your team — Aviagent proposes the applicable set and shows its reasoning; your engineers confirm every determination and sign off. The output isn't just a number; it's a documented, timestamped evidence chain from the directive to the decision, ready to defend in your next audit.

That's the difference between an alert and an answer: an alert tells you an AD exists; the answer tells you what it means for your fleet — and proves it.

FAQ

Does every AD for my aircraft type apply to my aircraft? No. An AD written against your type still has to match your specific aircraft's serial number, modification state, installed part numbers, and — for powerplant ADs — engine variant. Effectivity narrows a type-level directive down to specific tails.

What decides whether an AD applies? The directive's applicability/effectivity statement matched against the aircraft's type certificate (TCDS), model/variant, serial number (often within a range), configuration and mod state, and engine/propeller variant.

If I comply with an EASA AD, do I still need the FAA one? Usually the two are the same underlying directive and the comply-once principle applies — but only if you've correctly linked them. Track them as equivalents so you neither double-count nor miss a cross-jurisdiction AD.

Isn't a free AD email alert enough? An alert tells you a directive was published. It can't read effectivity against your fleet's serial numbers, mod states, or engine variants, so it can't tell you whether the AD applies to any specific aircraft. That determination is the actual work.

Does software make the applicability decision for me? Aviagent computes the applicable set and shows its reasoning, but every determination and sign-off is confirmed by qualified airworthiness engineers. It's a decision-support tool — engineering judgement stays with your team.

See which ADs apply to your fleet — free, in about 30 seconds. Try the free AD lookup, or book a 20-minute walkthrough.

Related reading: EASA vs FAA ADs — comply-once and cross-references · AD deadlines: flight hours, cycles and calendar limits · Building an audit-ready AD evidence chain.

About the author — Satya Neerupudi is Founder & CEO/CTO of Aviagent and an aeronautical engineer with 25 years in continuing airworthiness at SAS, GE Aviation, Pratt & Whitney, and HAL.