The Aircraft Flight Manual is the one document on the airplane that is simultaneously a legal limitation, an operating reference, and a moving target. It defines what you are allowed to do with the aircraft — and the moment someone installs new avionics, a cargo door, a winglet kit, or an auxiliary fuel system, a piece of that manual is supposed to change with it. The AFM you are required to have aboard is not a static binder; it is the baseline plus every supplement that matches what is actually bolted to the airframe.
That is where operators get tripped up. The supplemental type certificate gets installed, the work gets signed off — and the AFM Supplement that should have gone into the cockpit manual either never makes it in, or goes in and then lingers after the equipment is removed. Either way the manual no longer describes the airplane. The recordkeeping that keeps this honest lives across a handful of CFR sections: 14 CFR §21.5 (the manual furnished with the aircraft), §91.9 (operate within it, and keep a current approved copy aboard), §21.113 (the STC behind most supplements), §43.9 (the alteration entry that installs it), and §91.417 (the Form 337 that becomes a life-of-aircraft record).
This guide walks each layer in order: when an AFM is required and what must be aboard, the difference between the baseline AFM and an AFMS, how an STC alteration drives a supplement and a maintenance entry, and the records you have to keep to prove the two agree. It is a companion to our master index of what records a Part 135 operator must keep and to the broader Part 91 aircraft records requirements guide.
Why the AFM Is a Recordkeeping Problem, Not Just a Binder in the Seatback
Most pilots think of the Aircraft Flight Manual as reference material — the place you look up a V-speed or an emergency checklist. That is true, but it understates what the manual is doing legally. The operating limitations in the approved AFM are binding: under §91.9(a), operating outside them is a violation in itself, independent of whether anything went wrong. And under §91.9(b)(1), the manual that has to be aboard is the current, approved one — which means it has to reflect the airplane's actual configuration today, not the day it left the factory.
The two most common failure modes are mirror images of each other. First, an orphaned modification: an STC was installed and signed off, but the AFM Supplement that documents its limitations and procedures never made it into the cockpit manual — so the crew is operating modified equipment against the unmodified baseline. Second, a stale supplement: an AFMS sits in the binder for equipment that was later removed, so the manual carries limitations and procedures for hardware that is no longer on the airplane. In both cases the manual aboard no longer matches the aircraft, and the records cannot reconcile the two.
Two Documents That Have to Agree
- In the cockpit — the current, approved AFM = baseline + every applicable AFMS §91.9(b)(1)
- In the records — the §43.9 alteration entry + Form 337 for each major modification §43.9 / §91.417
- On the airplane — the equipment actually installed, which both of the above must match
The rest of this guide takes each layer in turn. If you only remember one thing: the AFM aboard, the alteration records, and the installed equipment all have to tell the same story — one STC modification, one AFMS in the manual, one §43.9 entry (and Form 337 if major) in the records.
When an AFM Is Required and What Must Be Aboard: §21.5 and §91.9
Two sections set the frame. §21.5 is the furnishing rule — it puts a Flight Manual into the owner's hands at delivery. §91.9 is the operating rule — it binds you to the manual's limitations and requires the current approved copy to be available in the aircraft.
"With each airplane or rotorcraft not type certificated with an Airplane or Rotorcraft Flight Manual and having no flight time before March 1, 1979, the holder of a type certificate (including amended or supplemental type certificates) or the licensee of a type certificate must make available to the owner at the time of delivery of the aircraft a current approved Airplane or Rotorcraft Flight Manual."
— 14 CFR §21.5(a)
The practical effect of §21.5(a) is that essentially every airplane and rotorcraft certificated and delivered since that March 1, 1979 cutoff comes from the manufacturer with an FAA-approved Flight Manual. Older type designs and many smaller aircraft were certificated without a formal AFM and instead rely on approved manual material, markings, and placards. That distinction is exactly why §91.9 has two branches:
§91.9(b)(1) — AFM required
For a U.S.-registered civil aircraft for which an Airplane or Rotorcraft Flight Manual is required by §21.5, no person may operate it unless there is available in the aircraft a current, approved Flight Manual (or the manual material provided for in §121.141(b)). This is the branch that covers virtually all post-1979 turbine and modern aircraft.
§91.9(b)(2) — AFM not required
For a U.S.-registered civil aircraft for which a Flight Manual is not required, no person may operate it unless there is available in the aircraft a current approved Flight Manual, approved manual material, markings and placards, or any combination thereof. This is the branch that covers many older and smaller aircraft.
And sitting above both branches is the limitation itself. §91.9(a) provides that no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards. So the chain is: §21.5 puts the manual in your hands, §91.9(b) requires the current approved version to be aboard, and §91.9(a) makes its limitations binding on every flight.
"Current" means current with the airplane's configuration
The word that does the work in §91.9(b)(1) is current. A Flight Manual is not current just because it is the latest revision the manufacturer published for the baseline type — it is current when it reflects the airplane as configured, including every AFMS for the modifications actually installed. An airplane with an STC'd avionics suite whose AFM lacks the matching supplement is, in practice, flying without a current approved Flight Manual for that equipment. This is the kind of configuration-driven currency a records system that knows what is installed helps you keep straight.
Worth noting on content: §21.5(b) specifies what the furnished Flight Manual must contain — the operating limitations and information required by the applicable regulations, the maximum ambient atmospheric temperature for engine cooling where the performance section does not otherwise require it, and, where applicable, documentation of compliance with part 38 (the fuel-efficiency certification standard). For day-to-day operations, the operative point is simpler: the limitations portion is the FAA-approved part, and that is what §91.9(a) binds you to.
AFM vs. AFM Supplement: Baseline and the Layers on Top
The cleanest way to think about it: the AFM is the airplane as type certificated, and each AFMS is a layered modification documented on top of it. The baseline AFM carries the operating limitations, normal and emergency procedures, and performance data for the certificated aircraft. An AFM Supplement adds or revises those items to account for a specific alteration — and the most common source of an AFMS is a supplemental type certificate.
The baseline AFM
- Documents the aircraft as type certificated
- Operating limitations (the FAA-approved part)
- Normal, abnormal, and emergency procedures
- Performance data for the certificated configuration
An AFM Supplement (AFMS)
- Documents how one modification changes the baseline
- Revised limitations or procedures for that equipment
- Typically supplied with the STC that authorizes the change
- Inserted into the manual when the modification is installed
Approved vs. informational — handle carefully
Not every page added to a Flight Manual is an FAA-approved limitation. The portion that carries operating limitations is the approved part — that is what §91.9(a) binds you to, and what an AFMS from an STC typically revises in an FAA-approved manner. Manufacturers and STC holders also issue informational and guidance material (pilot operating handbook content, supplementary procedures, reference data) that supports operations but is not, by itself, the approved limitation. When the status of a particular supplement is unclear, the approval block on the document itself, and your A&P or IA, is the authority — not a general assumption. We describe the approved/informational distinction here cautiously because it turns on the specific document, not a blanket rule.
The records consequence is the one that matters: the current, approved AFM §91.9(b)(1) requires aboard is the baseline manual plus every AFMS that applies to the modifications actually installed — never the baseline alone once the airplane has been modified, and never a binder that still carries supplements for equipment that has been removed.
Does Your AFM Match Your Airplane?
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Run the FAA Readiness Score — FreeHow an STC Alteration Drives a Supplement — and a Maintenance Entry
This is the layer that sits at the seam between maintenance and operations, and the one operators most often get wrong. A supplemental type certificate is the FAA approval for a major design change to a type-certificated product that does not require a brand-new type certificate. When that approval is installed on a specific aircraft, two separate records have to come into existence — and they have to agree.
§21.113 — The STC behind the supplement
Under §21.113, a person who holds the type certificate for a product and makes a major design change that does not require a new TC must apply either for a supplemental type certificate or to amend the original type certificate; a person who does not hold the TC must apply to the FAA for an STC. The application must be made in the form and manner prescribed by the FAA. The STC is what authorizes the modification — and the FAA-approved AFMS that documents the modification's limitations and procedures is typically issued as part of that STC.
The AFMS gets inserted into the manual
When the STC is installed, the technician inserts the matching FAA-approved AFM Supplement into the aircraft Flight Manual. From that point, the limitations and procedures for the modified equipment live in the AFMS, layered on the baseline AFM. This is the step that makes the manual current for the new configuration under §91.9(b)(1) — and the step most often skipped, leaving an orphaned modification.
§43.9 — The alteration entry that records the install
Installing an STC is an alteration, and §43.9(a) requires the maintenance record entry to contain: a description of (or reference to data acceptable to the Administrator for) the work performed; the date of completion of the work; the name of the person performing the work if other than the person approving it; and the signature, certificate number, and kind of certificate held by the person approving the work for return to service. (Inspections are recorded separately — §43.9 does not apply to persons performing inspections under the parts and sections listed in §43.9(c); those entries follow the §43.11 inspection-entry rules.)
§43.9(d) — A major alteration goes on FAA Form 337
If the STC installation is a major alteration, §43.9(d) requires it to be entered on a form and the form disposed of in the manner prescribed in Appendix B to Part 43 — the FAA Form 337. Form 337 is the document that records the major alteration and references the approved data (the STC) under which it was performed. Most equipment-installation STCs are major alterations, so a Form 337 is the norm, not the exception.
§91.417(a)(2)(vi) — The Form 337 is a record that follows the airplane
Under §91.417(a)(2)(vi), a copy of the forms prescribed by §43.9(d) — the Form 337 — for each major alteration to the airframe and the currently installed engines, rotors, propellers, and appliances is part of the records the owner or operator must retain. And under §91.417(b), those §91.417(a)(2) records are transferred with the aircraft when it is sold. So the STC modification's paper trail isn't transient: the Form 337 (and the approved data behind it) travels with the airplane. See our full airworthiness records guide for how this slots into the permanent-record set.
The trap: the modification and the manual drift apart
The failure mode is quiet. The STC gets installed, the §43.9 entry gets made, the Form 337 gets executed — but the AFM Supplement never goes into the cockpit manual, so the airplane is flying modified equipment against the unmodified baseline AFM. Or the reverse: a modification is removed and its §43.9 removal entry is made, but the AFMS is left in the binder, so the manual carries limitations for hardware that is gone. The fix is procedural and pairs the two records: every modification that gets a §43.9 entry should trigger a matching AFMS action (insert on install, remove on removal), and every AFMS in the manual should have a §43.9 entry and, if major, a Form 337 behind it. The reconciliation — manual against records against installed equipment — is exactly what an inspector can do, so it is what you should do first.
One clarification worth making: §43.9 governs the alteration record entry and §43.9(d) the form for a major alteration — neither section uses the phrase "AFM supplement" in its operative text. The reason an STC drives an AFMS is that the STC's approved data includes the supplement, and inserting it is what keeps the Flight Manual current for the modified configuration under §91.9. The two documents are created by different rules and different people — the AFMS by the STC/approved data, the §43.9 entry and Form 337 by the installer — which is precisely why they have to be reconciled rather than assumed to match.
Where the AFM Records Live — Cockpit vs. Permanent File
AFM-related records split across two homes, and conflating them is a common mistake. One set has to be aboard the aircraft; the other set lives in the permanent maintenance records that follow the airplane. Knowing which is which is half the battle in an inspection.
Aboard the aircraft
- The current, approved AFM — baseline plus every applicable AFMS (§91.9(b)(1))
- Or, where an AFM is not required, approved manual material, markings, and placards (§91.9(b)(2))
- A supplement set that matches the equipment actually installed — nothing missing, nothing orphaned
In the permanent records
- The §43.9 alteration entry for each STC installation
- A Form 337 for each major alteration (§43.9(d) / Appendix B)
- The STC and its approved data / instructions for continued airworthiness
- Retained and transferred with the aircraft on sale (§91.417(a)(2)(vi) / §91.417(b))
For Part 135 operators: the manual question is layered
Part 135 operators carry the same §91.9 obligation for the AFM aboard each aircraft, but they also maintain a separate operational layer — the company general operations and maintenance manuals, and operations specifications, that govern how the operator runs. Those are different documents from the per-aircraft AFM and its supplements. See the Part 135 GOM/GMM manual requirements and the full Part 135 records index for how the company manuals sit alongside each aircraft's Flight Manual. Aircraft maintained under a continuous airworthiness maintenance program have their inspection and records framework set by the program rather than the §91.409 default — but the AFM-aboard requirement of §91.9 still applies.
The through-line: the AFMS itself rides in the cockpit Flight Manual, and the paper trail that proves it was properly installed — the §43.9 entry and the Form 337 — rides in the permanent records. A pre-purchase buyer or an FAA inspector will pull both and check that they describe the same airplane. The connection to weight and balance is worth flagging too: an alteration that changes operating limitations or flight data also drives a weight-and-balance recomputation, so an AFMS, a Form 337, and a revised W&B can all originate from a single modification.
The AFM & AFMS Records Checklist
Pulling the layers together, here is what a complete Flight Manual records picture looks like. An inspector or a pre-purchase reviewer will work down a list like this — reconciling the manual aboard, the alteration records, and the installed equipment — and so should you, before they do.
1. The Manual Aboard (§91.9 / §21.5)
- A current, approved Airplane or Rotorcraft Flight Manual available in the aircraft where an AFM is required (§91.9(b)(1))
- Or, where an AFM is not required, current approved manual material, markings, and placards (§91.9(b)(2))
- The baseline AFM at the correct revision for the type
- Every AFM Supplement that applies to a modification actually installed — present and matching
- No supplements in the binder for equipment that has been removed
2. STC & Supplement Documentation (§21.113)
- The supplemental type certificate (or amended TC) authorizing each major design change
- The FAA-approved AFM Supplement supplied with each STC, inserted into the Flight Manual
- The STC approved data and instructions for continued airworthiness retained in the records
- Clear status on whether each supplement page is an approved limitation or informational material
3. Alteration Records (§43.9 / §91.417)
- A §43.9 maintenance record entry for each STC installation (work performed, date, name, signature/certificate number/kind of certificate of the approver)
- An FAA Form 337 for every major alteration (entered and disposed of per §43.9(d) and Appendix B to Part 43)
- Each Form 337 retained as a §91.417(a)(2)(vi) record and transferred with the aircraft on sale (§91.417(b))
- Removal entries for any modification taken off the airplane, paired with removal of the matching AFMS
4. Reconciliation
- A one-to-one match: every installed STC modification has its AFMS in the manual and its §43.9 entry (and Form 337 if major) in the records
- No orphaned modifications (installed but no supplement) and no stale supplements (supplement but no installed equipment)
- Any limitation- or flight-data change also reflected in weight and balance where applicable
- Operating limitations honored on every flight per §91.9(a)
How FileFlo Sits in the AFM Records Stack
FileFlo is a compliance document intelligence platform — a read-only proof layer that sits alongside your existing maintenance-tracking and records workflow and keeps the documents audit-ready. It classifies 600+ document types against the governing CFR section, so an STC and its approved data get tagged to the alteration record set, a Form 337 gets recognized as a §91.417(a)(2)(vi) life-of-aircraft record, and an AFM Supplement gets indexed alongside the modification it documents. It tracks the documents that carry dates, surfaces what is missing, and generates inspector-format audit binders on demand.
FileFlo does not maintain your Aircraft Flight Manual, insert or remove AFM Supplements, perform alterations, file your Form 337, or substitute for your DOM, A&P, IA, or maintenance-tracking system — and the current, approved AFM still has to be aboard the aircraft under §91.9(b)(1). It keeps the documents that prove your AFM and modification status — the STC paperwork, the AFMS revisions, the §43.9 entries, and the Form 337 copies — organized, indexed against the relevant CFR, and ready for an FAA inspector or a buyer's pre-purchase review.
Related Aviation Compliance Guides
What Records Must a Part 135 Operator Keep?
The master index of every Part 135 record, CFR cite, and retention period
Part 91 Aircraft Records Requirements
Permanent vs temporary records and the §91.417 / §91.419 framework
FAA Form 337: Major Repair & Alteration Records
How the Form 337 documents an alteration and why a copy lives forever
§43.9 Maintenance Record Entry Requirements
What every maintenance and alteration entry must contain
Aircraft Weight & Balance Records
How an alteration drives a W&B recomputation and a Form 337
ARROW Documents Aboard the Aircraft
Airworthiness, Registration, Radio, Operating limits, Weight & balance
Airworthiness Directive Compliance Records
How Part 39 AD tracking works and what gets operators cited
Prepare for a Part 135 FAA Surveillance Audit
What inspectors ask for and how to be ready
Frequently Asked Questions
What does 14 CFR §91.9 require for the Aircraft Flight Manual to be aboard?
14 CFR §91.9 has two parts. Section 91.9(a) prohibits operating any civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards. Section 91.9(b) then addresses what must be physically available in the aircraft: under §91.9(b)(1), for a U.S.-registered civil aircraft for which an Airplane or Rotorcraft Flight Manual is required by §21.5, no person may operate it unless there is available in the aircraft a current, approved Flight Manual (or the manual material provided for in §121.141(b)); under §91.9(b)(2), for a U.S.-registered civil aircraft for which a Flight Manual is not required, no person may operate it unless there is available in the aircraft a current approved Flight Manual, approved manual material, markings and placards, or any combination thereof. In plain terms: you must operate within the AFM, and where an AFM is required it has to be current, approved, and on board.
When is an aircraft actually required to have a Flight Manual under §21.5?
14 CFR §21.5(a) provides that with each airplane or rotorcraft not type certificated with an Airplane or Rotorcraft Flight Manual and having no flight time before March 1, 1979, the holder of the type certificate (including amended or supplemental type certificates) or the licensee of a type certificate must make a current approved Flight Manual available to the owner at the time of delivery. The practical effect is that essentially every airplane and rotorcraft certificated and delivered since that 1979 cutoff comes with an FAA-approved Flight Manual, and §91.9(b)(1) requires that manual to be aboard. Many older type designs and smaller aircraft were certificated without a formal AFM and instead rely on approved manual material, markings, and placards — which is exactly the situation §91.9(b)(2) covers. The §21.5(b) Flight Manual content also includes the operating limitations and information required by the applicable regulations and, where applicable, documentation of compliance with part 38.
What is the difference between an AFM and an AFM Supplement (AFMS)?
The Aircraft Flight Manual (AFM) is the baseline manual that documents the aircraft as it was type certificated — its operating limitations, normal and emergency procedures, and performance data. An AFM Supplement (AFMS) is an addition or revision to that baseline that documents how a specific alteration changes those limitations, procedures, or performance. The most common driver is a supplemental type certificate (STC): when an STC adds equipment or modifies the aircraft, the STC typically comes with an FAA-approved AFMS that the installing technician inserts into the aircraft Flight Manual. So the AFM describes the certificated airplane and each AFMS describes a layered modification on top of it. From a records standpoint, the current, approved AFM required aboard under §91.9(b)(1) is the baseline plus every AFMS that applies to the modifications actually installed — not the baseline alone.
How does an STC alteration drive an AFM Supplement and a maintenance record entry?
An STC is the FAA approval for a major design change that does not require a new type certificate. Under 14 CFR §21.113, a type-certificate holder making such a change applies for an STC or to amend the type certificate, while a person who does not hold the TC applies for an STC. When that STC is installed on a specific aircraft, the installation is an alteration that must be recorded under 14 CFR §43.9: §43.9(a) requires the entry to contain a description of (or reference to data acceptable to the Administrator for) the work performed, the date of completion, the name of the person performing the work if different from the approver, and the signature, certificate number, and kind of certificate held by the person approving the work for return to service. If the STC installation is a major alteration, §43.9(d) requires it to be entered on a form and the form disposed of in the manner prescribed in Appendix B to Part 43 — the FAA Form 337. The AFMS supplied with the STC is the document that updates the limitations and procedures; the §43.9 entry (and Form 337 for a major alteration) is the document that proves the modification was installed and approved. They are two different records that have to agree.
Is every AFM Supplement FAA-approved, or are some informational?
Not every supplement to a Flight Manual is an FAA-approved limitation. The portion of an AFM that carries operating limitations is the approved part — that is what §91.9(a) binds you to and what an AFMS supplied with an STC typically revises in an FAA-approved manner. Manufacturers and STC holders also issue informational or guidance material — pilot operating handbook sections, supplementary procedures, and reference data — that is helpful but is not, by itself, the FAA-approved limitation. The cautious way to treat it: the FAA-approved AFM and any FAA-approved AFMS for an installed modification set the limitations you must operate within and must be current and aboard; informational material supports operations but does not replace the approved limitations. When a document is ambiguous, the approval status on the supplement itself, and your A&P or IA, is the authority — not a general assumption.
What AFM records does the operator have to keep, and where do they live?
Three things. First, the current, approved AFM (baseline plus every applicable AFMS) has to be available in the aircraft per §91.9(b)(1) where an AFM is required — that is an aboard-the-aircraft requirement, not a back-office file. Second, the alteration records that put each AFMS there live in the aircraft maintenance records: the §43.9 entry for each modification, and an FAA Form 337 for each major alteration. Third, under 14 CFR §91.417(a)(2)(vi), a copy of each Form 337 for a major alteration to the airframe and currently installed engines, rotors, propellers, and appliances is part of the records the owner or operator must retain, and under §91.417(b) those §91.417(a)(2) records are transferred with the aircraft when it is sold. So the AFMS itself rides in the cockpit manual, while the paper trail proving it was properly installed rides in the permanent records that follow the airplane.
What goes wrong with AFM and AFMS records in a Part 135 or Part 91 inspection?
The recurring findings are mismatches and staleness. An STC was installed but the matching AFMS was never inserted, so the cockpit manual does not reflect the modification flying on the airplane. Or the reverse: an AFMS is in the binder for equipment that was later removed, leaving limitations that no longer apply. Or the baseline AFM revision aboard is superseded. Or there is an AFMS but no §43.9 entry and no Form 337 to back it, so the records cannot prove the modification was approved. Because the AFM has to be current and aboard under §91.9(b)(1), and the alteration paperwork has to exist under §43.9 and §91.417, an inspector can cross-check the two against each other and against the equipment actually installed. The clean state is a one-to-one match: every installed STC modification has its AFMS in the manual and its §43.9 entry (and Form 337 if major) in the records, and nothing is in the manual that is not on the airplane.
Does FileFlo manage the Aircraft Flight Manual or keep my AFM current?
No. FileFlo is a compliance document intelligence platform — a read-only proof layer. It does not maintain your Aircraft Flight Manual, insert AFM Supplements, perform alterations, or substitute for your A&P, IA, or maintenance-tracking system, and the current, approved AFM still has to be aboard the aircraft per §91.9(b)(1). What FileFlo does is keep the document trail audit-ready: it classifies the records that prove your AFM and AFMS status — the STC paperwork, the AFMS revisions, the §43.9 alteration entries, and the FAA Form 337 copies — against the governing CFR section, indexes them, tracks the documents that carry dates, and generates inspector-format binders on demand. It proves the records are organized; it does not run the airplane.
Keep Your AFM & Supplement Records Audit-Ready
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Written by Chad Griffith, Founder, FileFlo — compliance document intelligence · Reviewed June 11, 2026 · Primary sources: 14 CFR §21.5, §91.9, §21.113, §43.9, Appendix B to Part 43, §91.417