An airworthiness directive is federal law and you must comply with every one that applies to your aircraft, engine, propeller or appliance. A manufacturer's service bulletin is a recommendation, and for a Part 91 owner flying privately it is not legally binding unless something else makes it binding. That is the short answer to service bulletin vs airworthiness directive, and it is the version most hangar conversations stop at.
The longer answer is where the money is. There are four specific situations in which a service bulletin you were told to ignore becomes just as mandatory as an AD, and plenty of owners find out about them during a pre-purchase inspection or an insurance claim. This article walks through who each document binds, what the deadlines really mean, what happens when you skip one, and how each shows up when you sell.
What the Two Documents Actually Are
An airworthiness directive is a rule issued by the FAA under 14 CFR Part 39. It is published in the Federal Register and it carries the same legal weight as any other federal aviation regulation. The FAA issues one when it finds an unsafe condition in a product and determines that the condition is likely to exist in other products of the same type design. Section 39.7 is blunt about the consequence: no person may operate a product to which an AD applies except in accordance with the requirements of that AD.
A service bulletin comes from the manufacturer — Textron, Piper, Lycoming, Continental, Hartzell, Garmin — and it is a technical communication, not a regulation. Manufacturers use a ladder of names: service letter, service information letter, service instruction, service bulletin, alert service bulletin, and mandatory service bulletin. Those labels describe how strongly the manufacturer feels. They do not describe your legal obligation. The word "mandatory" on the cover page is the manufacturer's word, not the FAA's.
Keep in Mind: The FAA cannot make a service bulletin binding by wishing it so, and a manufacturer cannot write regulations. When the FAA agrees that a bulletin addresses a real unsafe condition, it writes an AD that incorporates the bulletin by reference — at which point the bulletin's procedures become the legally required method of compliance.
That conversion happens often. The PA-28 and PA-32 wing spar inspection is a good example: Piper issued Service Bulletin 1345 after a 2018 in-flight wing separation, and the FAA later folded it into AD 2020-26-16, which requires owners to calculate factored service hours and inspect the lower main spar bolt holes. Before the AD, compliance was voluntary. After it, it was the law for every affected airframe on the U.S. registry.
Who Each Document Binds
The private, non-commercial Part 91 owner
If you own a Skyhawk, a Bonanza or a Cherokee and fly it for yourself, ADs are mandatory and service bulletins are not. Under 14 CFR 91.403(a) you, the owner or operator, are primarily responsible for maintaining the aircraft in airworthy condition, including compliance with Part 39. Nothing in Part 91 requires you to perform an un-AD'd service bulletin, no matter what the cover page says.
Lycoming's Service Instruction 1009 is the classic illustration. It publishes recommended time between overhaul figures, and plenty of owners treat those hours as a hard wall. They are not a legal limit for private Part 91 operation — we dig into that in Is Lycoming TBO a Legal Limit for Part 91?. Lycoming's ADs, on the other hand, are not optional at all, and there is a long list of them covered in Lycoming Airworthiness Directives.
The four exceptions that make a bulletin binding
A service bulletin stops being optional when any of these apply:
One, the FAA incorporated it into an AD. The AD text will name the bulletin and revision level, and that revision is what you must follow.
Two, it lives in the Airworthiness Limitations section. Under 14 CFR 91.403(c), if your aircraft's maintenance manual or instructions for continued airworthiness contain an airworthiness limitations section, the mandatory replacement times and inspection intervals in it must be complied with. Section 43.16 puts the same duty on the mechanic. This is how turbine life-limited parts and some airframe life limits become hard numbers — see Life Limited Parts Explained.
Three, a service bulletin contains inspections incorporated into your selected inspection program. Under 14 CFR Section 91.409(f)(3), an operator who selects the manufacturer's recommended inspection program must follow its required inspections, including inspection requirements contained in service bulletins incorporated into that program when it was adopted. However, this does not automatically make every manufacturer-recommended repair, modification or equipment upgrade mandatory. Other maintenance actions become legally required when an applicable AD, airworthiness limitation or other regulatory requirement mandates them.
Four, an operating requirement or private agreement applies. A Part 135 operator's approved maintenance program or operations specifications may require particular service bulletin actions. Separately, a lease, lender agreement, warranty or insurance policy may establish contractual obligations. Part 145 repair stations must follow their applicable regulatory and approved procedural requirements, but those requirements do not automatically make every service bulletin mandatory for an aircraft owner. Regulatory violations and breaches of private contracts have different consequences.
Heads Up: If you put your airplane on a leaseback with a flight school that operates under Part 135, you have changed the rulebook that applies to it. Bulletins that were advisory on Monday can be required by the operator's opspecs on Tuesday.
Flying411 keeps aircraft listings, specifications and ownership guidance in one place, so you can compare how two candidate airframes stack up on open directives before you make an offer.
Deadlines, Relief and What Compliance Costs
Every AD states its own compliance time. Some read "before further flight." Some give you a window such as the next 50 hours time in service, or the next annual inspection, or a calendar date. Recurring ADs then repeat on an interval, and tracking that interval is on you. Our explainer on one-time versus recurring AD compliance covers how to keep that status current.
Service bulletins carry recommended compliance times instead — "at next overhaul," "within 100 hours," "at owner's convenience." Miss one and nothing legally happens.
If an AD is genuinely impractical for your aircraft, you are not stuck. Section 39.19 lets you request an alternative method of compliance, approved by the FAA office named in the AD itself. And if the airplane is out of compliance where it sits, a special flight permit under 21.197 may let you ferry it to a shop — unless the AD specifically forbids further flight. Both routes take paperwork and time, so start them before the deadline, not after.
Good to Know: Every AD published in the Federal Register includes the FAA's own estimate of the cost of compliance, broken into labor hours and parts. It is a useful sanity check when a shop quote looks high, though the FAA figure assumes nothing goes wrong once the panel is off.
What Skipping One Actually Costs You
An overdue AD makes the aircraft unairworthy. That one fact drives everything else. Under 91.7 the pilot in command is responsible for determining the aircraft is in condition for safe flight, and flying with an open AD is a violation of both 39.7 and 91.403. The FAA can pursue certificate action against the pilot and civil penalties against the operator.
Your insurer is the second problem. Most policies condition coverage on the aircraft holding a valid airworthiness certificate and being maintained in airworthy condition. An open AD discovered after a claim gives an underwriter a reason to argue, and that argument is expensive even when you eventually win it.
Your IA is the third. At annual, the inspector must determine AD compliance status before signing the aircraft as airworthy. If an AD is overdue, the inspection can still be completed, but the sign-off becomes a list of discrepancies rather than an approval for return to service. An open service bulletin does not force that outcome — though a good IA will tell you about it in writing, and you should keep that note. The broader picture of who owes what is laid out in Compliance Rules: What Is the Responsibility of Aircraft Owner.
Why It Matters: Think of an AD like a recall notice on a car that also suspends your registration until it is done. A service bulletin is closer to the dealer calling to say a better part is available. Both are worth reading; only one keeps you on the ground.
Records and Resale
Section 91.417(a)(2)(v) requires your maintenance records to show the current status of applicable airworthiness directives, and for each one: the method of compliance, the AD number and revision date, and — if it recurs — the time and date when the next action is due. Those records transfer with the aircraft when you sell it.
That is why a sloppy AD list costs real money at sale. A buyer's mechanic will build an AD report against the airframe, engine, propeller and appliances, then compare it line by line with your logs. A missing method-of-compliance entry is treated as non-compliance until proven otherwise, and the fix is usually to redo the work. Our aircraft owner maintenance guide walks through how to keep that paperwork defensible.
Open service bulletins behave differently in a negotiation. They are not a legal defect, so they rarely kill a deal — but a well-known bulletin that a buyer expects to see done, such as a crankshaft or fuel-system inspection on a popular engine, becomes a price adjustment. Sellers who complete the headline bulletins and keep the invoices usually recover most of the cost in a smoother sale.
Flying411 keeps maintenance, ownership and valuation articles in one place, so you can compare what a clean logbook is worth against what an open directive takes off the price.
Key Takeaways
Airworthiness directives are regulations under 14 CFR Part 39 and apply to every U.S.-registered aircraft they name, with no Part 91 exemption and no shop-owner discretion.Service bulletins are generally advisory for private Part 91 operations unless applicable requirements are incorporated into an AD, an approved Airworthiness Limitations section or another binding regulatory requirement. Inspection tasks incorporated into a selected manufacturer inspection program may also become mandatory, while contracts, warranties and insurance policies can create separate obligations. The word "mandatory" printed on a bulletin changes nothing about federal law, but it changes a great deal about what a buyer, an underwriter and an overhaul shop will expect to see in your logs. When an AD is genuinely unworkable, 39.19 gives you an alternative method of compliance and 21.197 may give you a ferry permit — both of which take lead time. The practical rule: never defer an AD, and treat each bulletin as a business decision about safety, resale and warranty rather than a legal one.
| Dimension | Airworthiness Directive | Service Bulletin |
| Issued by | FAA (foreign authority for non-U.S. type certificates, adopted by FAA) | Type certificate holder or component manufacturer |
| Legal basis | 14 CFR Part 39; published in the Federal Register | None; technical guidance only |
| Binding on private Part 91? | Yes, always (14 CFR 39.7, 91.403(a)) | No, unless cited in an AD, in the Airworthiness Limitations section (91.403(c), 43.16), or in a selected 91.409(f) program |
| Binding on Part 121/135? | Yes | Often yes, through operations specifications or an approved maintenance program |
| Deadline language | Fixed: "before further flight," hours in service, or calendar date, stated in the AD | Recommended: next overhaul, next inspection, or owner's convenience |
| Record-keeping duty | Status, method of compliance, AD number, revision date and next due time required by 91.417(a)(2)(v) | No regulatory entry required; log it anyway for resale |
| Relief available | Alternative method of compliance under 39.19; special flight permit under 21.197 if not prohibited | Not applicable — compliance is voluntary |
| Effect if overdue | Aircraft is unairworthy; FAA enforcement exposure; annual signed as discrepancies | Aircraft remains airworthy; may affect warranty, insurance terms or resale price |
| Effect at sale | Buyer's AD report compares logs line by line; gaps usually mean redoing the work | Usually a price negotiation item, not a deal breaker |
Conclusion
The practical way to settle service bulletin vs airworthiness directive for your own airplane is to build one list and ask one question of each item. Pull a current AD report for the airframe, engine, propeller and appliances, confirm every entry has a method of compliance and a next-due date in the logs, and fix any gap before your next annual. Then take each outstanding bulletin and ask whether an AD, an airworthiness limitation, your inspection program or a contract attaches it to you. If none do, decide on the merits — cost, safety benefit, what a future buyer will want to see — and write down what you decided. That record is worth having either way.
Flying411 keeps aircraft listings, maintenance explainers and owner guides in one place, so you can compare candidates on paperwork quality, not just hours and paint.
When you are ready to compare listings, visitFlying411 and see what is on the market today.
Frequently Asked Questions
Is a "mandatory service bulletin" actually mandatory for a Part 91 owner?
Not by itself. "Mandatory" is the manufacturer's label and carries no regulatory force for private Part 91 operation. It becomes mandatory only if the FAA incorporates it into an airworthiness directive, it appears in the Airworthiness Limitations section of the instructions for continued airworthiness, or your operation is bound to it through an approved inspection program or operations specifications.
Can my IA refuse to sign the annual because of an open service bulletin?
An IA should not reject an aircraft solely because an otherwise advisory service bulletin remains uncompleted. However, if the inspection reveals an unsafe condition, a violation of approved airworthiness limitations or another condition that makes the aircraft unairworthy, the IA must document the discrepancy regardless of whether a service bulletin addresses it. An overdue applicable AD also prevents approval for return to service until compliance is established.
Does my insurance care about service bulletins?
Policies generally require the aircraft to be airworthy, which makes an open AD a live problem at claim time. Bulletins usually matter only if your specific policy or a lender's agreement names them. Read the endorsements — some underwriters do attach bulletin compliance to coverage on particular models.
What if I cannot comply with an AD by its deadline?
Request an alternative method of compliance under 14 CFR 39.19 from the FAA office named in the AD, or apply for a special flight permit under 21.197 to ferry the aircraft to a shop, unless the AD prohibits further flight. Both take time to process, so file early rather than waiting for the deadline to pass.
Do ADs on my engine follow the engine or the airplane?
They follow the product. An AD written against an engine, propeller or appliance applies wherever that unit is installed, which is why a mid-time engine bought from another airframe brings its own AD history with it. Check the engine and prop logs separately from the airframe logs.
Who is legally responsible for AD compliance — me or my mechanic?
You are. Under 91.403(a) the owner or operator is primarily responsible for maintaining the aircraft in airworthy condition, including Part 39 compliance. The mechanic is responsible for the work performed and its record entry, but the duty to know what is due and to get it done sits with you.
