Direct Answer — the Determination in Four Sentences
Whether a repair or alteration is "major" or "minor" is decided by the definitions in 14 CFR §1.1 and illustrated by the lists in Appendix A to Part 43 — and that one call drives the recordkeeping. Minor work is documented with an ordinary §43.9(a) maintenance record entry, and an appropriately rated mechanic may approve the return to service. Major work additionally requires the form prescribed by §43.9(d) and Appendix B to Part 43 — in practice FAA Form 337 — and a higher return-to-service authority, typically an inspection authorization holder under §65.95(a)(1), a Part 145 repair station, or an air carrier under Part 121 or 135. Retention is asymmetric: under §91.417(a)(2)(vi), the form for each major alteration is a permanent record that transfers with the aircraft at sale, while major-repair documentation sits in the §91.417(a)(1) one-year-or-superseded tier.
Sources: 14 CFR §1.1, Appendix A to Part 43, 14 CFR §43.9, 14 CFR §91.417.
Almost every maintenance-records question downstream of a wrench turn answers to one earlier question: was the work major or minor? Get it right and the paperwork follows a clean path. Get it wrong — log a major alteration as a minor entry — and you create a gap in the §91.417(a)(2) permanent record set that the seller is later required to transfer, and that a buyer's prebuy team is trained to find. FAA civil penalties for recordkeeping violations under 49 U.S.C. § 46301 reach $75,000 per violation under 14 CFR §13.301 — but the routine cost is commercial: stalled transactions, devalued airframes, and conformity questions an operator cannot answer from its own files.
This article is the determination side of the story. For the mechanics of the form itself — who executes it, where the copies go, the 48-hour FAA clock, and the repair-station work-order exception — see the companion explainer on FAA Form 337: major repair vs major alteration records. Here we focus on the call that triggers all of it.
The Test Lives in §1.1 — Four Definitions, Two Pairs
14 CFR §1.1 defines four terms. "Major" is defined affirmatively for both repairs and alterations; "minor" is defined by subtraction.
Major repair — 14 CFR §1.1
§1.1 defines a major repair as "a repair: (1) That, if improperly done, might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or (2) That is not done according to accepted practices or cannot be done by elementary operations."
The conditional is the tell: a repair is major if improper performance could appreciably affect airworthiness qualities — the test weighs downside risk, not whether the repair was in fact done well.
Major alteration — 14 CFR §1.1
§1.1 defines a major alteration as "an alteration not listed in the aircraft, aircraft engine, or propeller specifications— (1) That might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or (2) That is not done according to accepted practices or cannot be done by elementary operations."
Two differences from the repair definition: the alteration must not be listed in the product specifications, and the airworthiness-effect test is direct — there is no "if improperly done" conditional.
And the other side: minor is whatever major is not
§1.1 does not give minor repairs and minor alterations independent content. A minor repair is defined simply as "a repair other than a major repair," and a minor alteration as "an alteration other than a major alteration." That structure matters: you do not test whether something is minor. You test whether it is major, and if it fails that test, it is minor by definition. The entire determination collapses to applying the two affirmative major definitions correctly.
One distinction the §1.1 family adds is a third bucket sitting inside "minor": preventive maintenance, which §1.1 defines as simple or minor preservation operations and the replacement of small standard parts not involving complex assembly operations, with the specific tasks listed in Appendix A(c) to Part 43. Preventive maintenance is always minor work, but it carries a privilege ordinary minor repairs do not: under §43.7(f) and §43.3(g), a certificated pilot may approve for return to service the preventive maintenance they personally performed, listed in Appendix A(c), on an aircraft they own or operate that is not used under Part 121, 129, or 135. Appendix A(c) only lists the eligible items; the return-to-service authority comes from §43.7(f) and §43.3(g). A minor repair that is not preventive maintenance still takes an appropriately rated mechanic to approve.
Repair and alteration are not interchangeable words
A repair restores a product to a serviceable condition after damage or wear; an alteration changes it from its type-certificated configuration. The §1.1 definitions track that difference precisely — the alteration definition adds the "not listed in the specifications" clause because an alteration, by nature, departs from the approved baseline. Calling an alteration a "repair" in a logbook does not change which §1.1 test applies, and it can route the record down the wrong retention path under §91.417.
Appendix A to Part 43 — the Worked Lists, by Product
Appendix A converts the abstract §1.1 definitions into enumerated examples. Paragraph (a) lists major alterations; paragraph (b) lists major repairs; each is organized into airframe, powerplant, propeller, and appliance. Paragraph (c) lists preventive maintenance separately.
Major alterations
Appendix A(a)Airframe
Alterations to listed parts and types — wings, tail surfaces, fuselage, engine mounts, control system, landing gear, and the like — when not listed in the aircraft specifications.
Powerplant
Engine conversions, replacement of structural parts with parts not approved for the purpose, installation of accessories not approved for the engine, and conversions for fuels of different ratings.
Propeller
Changes in blade or hub design, governor or control-system changes, and installation of propeller de-icing or feathering systems.
Appliance
Alterations of the basic design not made in accordance with manufacturer recommendations or an FAA directive, and changes affecting equipment such as radio and navigation gear.
Major repairs
Appendix A(b)Airframe
Repairs to primary structure — box beams, monocoque or semimonocoque wings or control surfaces, wing stringers and chord members, spars, spar flanges, members of truss-type beams, and similar load-carrying members.
Powerplant
Separation or disassembly of a crankcase or crankshaft of certain reciprocating engines, and structural welding or metalizing repairs to engine parts.
Propeller
Straightening of blades, repairs to or straightening of hubs, retipping, and overhaul of certain propeller governors and controllable propellers.
Appliance
Calibration and repair of instruments, work on certain radio equipment, and overhaul of certain components such as pressure-type fuel and oil valves.
The lists are examples, not a closed universe
Appendix A illustrates the §1.1 definitions; it does not exhaust them. A job that does not appear on any list can still be major if it meets the §1.1 test — for instance, if it might appreciably affect structural strength or flight characteristics, or if it cannot be done by elementary operations. The reverse is also true: superficial resemblance to a listed item does not automatically make a trivial job major. When the call is genuinely close, operators in practice take it to their Flight Standards District Office or an IA before starting, rather than litigating it after a Form 337 should already have been disposed of.
Notice the parallel structure: both major alterations and major repairs are sorted into the same four product families — airframe, powerplant, propeller, appliance. That is not cosmetic. It maps directly onto how §91.417 records are organized and onto the "currently installed" language in §91.417(a)(2)(vi): the major-alteration record follows the specific airframe, engine, rotor, propeller, or appliance it was performed on, which is why a propeller swap can carry — or strand — an alteration 337 with it.
Do your logbook entries and your 337s agree?
The most expensive determination errors are silent — a major alteration logged as a minor entry, with no matching form on file. FileFlo classifies maintenance documents as they enter your records, indexes them to the right tail, and surfaces alterations in the logbooks that have no corresponding Form 337 — before an inspector or a buyer does. See the full Aviation compliance coverage.
Walking the Determination — a Records-Driven Way to Think About It
The classification call is a technical judgment for qualified people, and nothing here substitutes for that. But the logical structure of the determination is worth seeing plainly, because it explains why the record obligation lands where it does.
Is it a repair or an alteration?
A repair restores; an alteration changes the type-certificated configuration. The two §1.1 major definitions differ — the alteration test adds the "not listed in the specifications" clause — so naming the activity correctly is the first fork.
Apply the affirmative "major" test from §1.1.
For a repair: could improper performance appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness — or is it beyond accepted practices or elementary operations? For an alteration: is it not listed in the specifications and does it carry those same effects, or is it beyond accepted practices or elementary operations? Appendix A(a)/(b) supplies worked examples.
If it fails the major test, it is minor — by definition.
There is no separate "minor" test to run. A repair that is not major is a minor repair; an alteration that is not major is a minor alteration. If the minor work is also on the Appendix A(c) preventive-maintenance list and the pilot conditions are met, the pilot-owner return-to-service privilege may apply.
Let the classification pick the record path.
Minor: a §43.9(a) maintenance record entry, mechanic return to service. Major: the §43.9(a) entry plus the Appendix B form (Form 337), executed in duplicate, with IA, repair-station, or air-carrier return to service — and, for a major alteration, a permanent §91.417(a)(2)(vi) record that transfers at sale.
Approved data and return to service are still separate steps
Even once a job is classified major, the determination is not the end. A major repair or alteration needs FAA-approved technical data behind it — an STC, manufacturer-approved data, AD instructions, or, where none exists, a field approval. §43.5 then makes both the §43.9 (or §43.11) record entry and the executed repair-or-alteration form preconditions to approving the product for return to service, and §43.5(c) requires that any resulting change to operating limitations or flight data in the approved flight manual be revised and set forth as prescribed in §91.9. That is also the moment to refresh weight and balance records — a major alteration routinely shifts empty weight and CG, and a stale W&B sheet is the classic companion finding to an alteration 337.
Why the Call Matters — Three Records Consequences
The major/minor determination is not a labeling exercise. It changes the form, the signature authority, and the retention clock.
The form
Minor work is a §43.9(a) maintenance record entry — a logbook line with a description, date, name, and the signing person's signature, certificate number, and kind of certificate. Major work adds the Appendix B form. See the Form 337 explainer.
The signature
An A&P may approve minor work for return to service. Major work needs more: an inspection authorization holder under §65.95(a)(1), a Part 145 repair station, or an air carrier under Part 121 or 135. §65.85(a) excludes major work from the airframe-rating privilege.
The retention
A major-alteration form is a permanent record under §91.417(a)(2)(vi), transferred at sale. A major-repair form sits in the §91.417(a)(1) tier — kept until repeated or superseded, or 1 year. Minor entries live in the logbooks under the same §91.417 framework. Full schedule: aviation records retention.
The asymmetry that trips people up
§91.417(a)(2)(vi) names the form for each major alteration as part of the permanent record set that, under (b)(2), must be retained and transferred with the aircraft at sale. It does not name major repairs there — those fall under §91.417(a)(1), which (b)(1) says must be retained until the work is repeated or superseded by other work or for 1 year. So the same Form 337, executed the same way, lives forever if it documents an alteration and only a year (on paper) if it documents a repair. Sensible practice ignores the floor and keeps every 337 permanently — discarding a major spar-repair form saves nothing and erases provenance the next buyer's structures specialist will want. The records that sit in that same permanent (a)(2) tier include AD compliance status, life-limited parts status, and time since overhaul.
For a Part 135 certificate holder, the determination surface is also a surveillance surface. When an inspector works the airworthiness side of a Part 135 surveillance audit, reconciling the installed configuration against the alteration record — the 337s, the STC paperwork, the ARROW documents — is routine, and the broader Part 135 records set has to hang together. A determination error does not announce itself; it sits quietly in the logbooks until someone reconciles paper against airframe.
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Get Your Readiness ScoreFive Ways the Determination Goes Wrong in the Records
Every one of these is an administrative failure, not a maintenance failure — which is exactly why disciplined document handling prevents all five.
A major alteration logged as a minor entry
The single most consequential error. Work that meets the §1.1 major-alteration test gets written up as an ordinary §43.9(a) line, so no Form 337 is executed, no copy is forwarded to the FAA, and the permanent (a)(2)(vi) record never exists. The installed modification is real; the paperwork that should follow it for the life of the aircraft is not. It surfaces at the next prebuy, when the buyer walks the airframe and asks for a form that was never made.
A repair and an alteration confused on paper
The §1.1 tests differ, and so do the retention tiers. An alteration mislabeled as a repair can be routed down the §91.417(a)(1) one-year path instead of the permanent (a)(2)(vi) path, and a repair dressed up as an alteration invites questions about why it is in the permanent set at all. Naming the activity correctly in the first place keeps the record on the right shelf.
A mechanic signing off work that needed an IA
A&P ratings under §65.85(a) exclude major repairs and major alterations from the return-to-service privilege. When a major job is misclassified as minor, a mechanic may approve a return to service they were never authorized to approve — a §43.7 authority problem layered on top of the missing Form 337. The fix is upstream: classify correctly, and the right signatory follows.
Preventive maintenance treated as if it carried no record duty
Preventive maintenance is minor, and a pilot-owner may approve the listed items under §43.7(f) and §43.3(g) — but it still requires a §43.9(a) maintenance record entry. "Minor" is not "undocumented." A logbook with no entries for owner-performed oil changes and tire replacements is a gap an inspector reads as missing maintenance, not as work that did not need recording.
The companion records left behind
A major alteration that changes empty weight, CG, or the equipment list ripples into weight and balance records, equipment lists, and — where limitations change — the flight manual under §43.5(c). The 337 gets executed; the companion documents lag. An inspector who finds a fresh alteration form next to a five-year-old weight and balance sheet has found two findings, not one.
Where FileFlo fits — the document layer, honestly scoped
FileFlo does not make the major/minor call, approve your data, or return your aircraft to service — those are technical judgments and acts of certificated people. What FileFlo does is make the paper trail those people create stay provable: it classifies Form 337s, work orders, maintenance releases, and logbook entries as they enter your records, indexes them to the right tail, separates the permanent §91.417(a)(2) set from the one-year (a)(1) tier, and shows you — before an inspector or a buyer does — which alterations in your logbooks have no matching form on file.
When the FSDO letter or the prebuy request arrives, the answer is an organized, audit-ready export instead of a week of folder archaeology.
Frequently Asked Questions
How do you decide whether a repair or alteration is major or minor?
The decision is governed by the definitions in 14 CFR §1.1, illustrated by the lists in Appendix A to Part 43. A repair is major if it, when improperly done, might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness, or if it is not done according to accepted practices or cannot be done by elementary operations. A major alteration is an alteration not listed in the aircraft, aircraft engine, or propeller specifications that might appreciably affect those same airworthiness qualities, or that is not done according to accepted practices or cannot be done by elementary operations. Anything that is not a major repair is, by definition in §1.1, a minor repair, and anything that is not a major alteration is a minor alteration. The classification is made before the work, because it decides who may approve the return to service and whether an FAA Form 337 is required.
What is the records consequence of calling work major versus minor?
It changes both the form you owe and who must sign it. Minor repairs and minor alterations are documented with an ordinary maintenance record entry under 14 CFR §43.9(a), and an appropriately rated mechanic may approve the return to service. Major repairs and major alterations must additionally be entered on a form and the form disposed of in the manner prescribed in Appendix B to Part 43 — in practice, FAA Form 337 — and the return to service requires a higher authority such as an inspection authorization holder under §65.95(a)(1), a Part 145 repair station, or an air carrier under Part 121 or 135. So the major/minor call is not academic: it determines whether a logbook line is enough or whether a federally tracked form, executed in duplicate with a 48-hour FAA copy, is owed.
Where is the list of major alterations and major repairs?
Appendix A to Part 43 is the enumerated list. Paragraph (a) lists major alterations, broken into (a)(1) airframe, (a)(2) powerplant, (a)(3) propeller, and (a)(4) appliance. Paragraph (b) lists major repairs in the same four product categories: (b)(1) airframe, (b)(2) powerplant, (b)(3) propeller, and (b)(4) appliance. Paragraph (c) is a separate list of preventive-maintenance tasks, which are minor work that never requires a Form 337. The appendix lists are examples that flesh out the §1.1 definitions; they are not a closed universe, so a job that is not on a list can still be major if it meets the §1.1 test.
If the work is not on the Appendix A list, is it automatically minor?
No. The Appendix A lists illustrate the §1.1 definitions; they do not replace them. A repair or alteration that does not appear on the list can still be major if it meets the §1.1 definition — for example, if it might appreciably affect structural strength or flight characteristics, or if it cannot be done by elementary operations. Conversely, a job that resembles a listed item but is genuinely trivial may still be minor. When a determination is genuinely borderline, operators in practice resolve it with their Flight Standards District Office or an inspection authorization holder before the work begins, because reclassifying after the fact means rebuilding a Form 337 disposition chain that should have started at the return to service.
Is preventive maintenance the same as a minor repair?
They overlap but are not identical. Preventive maintenance is its own defined category in 14 CFR §1.1 — limited operations that do not involve complex assembly operations, with a specific list of tasks in Appendix A(c) such as replacing tires, servicing batteries, lubrication, and replacing spark plugs. All preventive maintenance is minor work, and under §43.7(f) and §43.3(g) a certificated pilot may, under conditions, approve for return to service the preventive maintenance listed in Appendix A(c) that they personally performed on an aircraft they own or operate, when the aircraft is not used under Part 121, 129, or 135. A minor repair that is not on the preventive-maintenance list is documented the same way under §43.9(a), but it does not carry the pilot return-to-service privilege — it requires an appropriately rated mechanic.
Can a mechanic without an inspection authorization approve a major alteration?
No. The airframe-rating privilege in 14 CFR §65.85(a) expressly applies to maintenance and alteration excluding major repairs and major alterations — the parenthetical is the whole point. A mechanic may perform a major repair or major alteration, but approving it for return to service is a separate authority. §65.95(a)(1) gives an inspection authorization holder the privilege to inspect and approve for return to service any aircraft or related part or appliance after a major repair or major alteration done in accordance with Part 43, if the work was done in accordance with technical data approved by the Administrator. Repair stations approve under Part 145 and air carriers under Part 121 or 135. The common small-shop pattern is two signatures: the mechanic who did the work executes the Form 337, and an IA inspects and approves the product for return to service against the approved data.
Does a minor alteration ever need a Form 337?
No. The Form 337 obligation in §43.9(d) and Appendix B to Part 43 applies only to major repairs and major alterations. A minor alteration — an alteration other than a major alteration under §1.1 — is documented with a §43.9(a) maintenance record entry and does not require a Form 337. The practical risk runs the other way: work that should have been classified as major gets logged as a minor entry, leaving no 337, no FAA-forwarded copy, and a gap in the permanent record set for alterations under §91.417(a)(2)(vi) that surfaces years later at a prebuy or a records review.
How long do the records of a major alteration have to be kept?
Under §91.417(a)(2)(vi), copies of the forms prescribed by §43.9(d) for each major alteration to the airframe and currently installed engines, rotors, propellers, and appliances are part of the records that must be retained and transferred with the aircraft at the time it is sold — effectively the life of the aircraft. Major-repair documentation falls in the §91.417(a)(1) bucket, which must be retained until the work is repeated or superseded by other work or for 1 year after the work is performed. That asymmetry is a floor, not a target: in practice operators and prebuy inspectors treat every Form 337, repair or alteration, as a permanent record, because the cost of keeping it is nothing and the cost of a provenance gap is a stalled transaction. Note that §91.417 does not apply to aircraft maintained under a continuous airworthiness maintenance program per §91.401(b); those operators keep equivalent records under their air-carrier rules.
Related Aviation Compliance Reading
FAA Form 337: Major Repair vs Major Alteration
The form the major determination triggers — who executes it, where copies go
14 CFR §43.9 Maintenance Record Entry Requirements
The data every maintenance entry — major or minor — must contain
Preventive Maintenance Records (Appendix A(c))
The minor-work category with a pilot-owner return-to-service privilege
Part 91 Aircraft Records Requirements
The full §91.417 record set and the (a)(2) permanent tier
Aircraft Weight & Balance Records
The companion document every major alteration touches
When Is a Form 337 Required?
The disposition rules, the 48-hour FAA copy, and the work-order exception
Classify it right; prove it later
FileFlo is a compliance document intelligence platform: it classifies aviation maintenance documents against the governing CFR — §43.9(a) entries, Form 337s under §43.9(d) and Appendix B, the §91.417(a)(2) permanent record set, repair-station work orders and maintenance releases — tracks what must transfer at sale, and generates inspector-format audit binders on demand. It proves your records; your A&P, IA, repair station, and FSDO still run the aviation. Starter $89/month · Professional $299/month · 5-day free trial, no credit card required.