Major or Minor Repair? A Field Guide for A&P Mechanics and Light-Aircraft Owners Under 14 CFR Part 43 Appendix A

A repair is major when 14 CFR Part 43 Appendix A lists it. For airframes, that means repairs that strengthen, reinforce, splice or manufacture primary structural members (spars, engine mounts, longerons, wing main ribs and more), plus specific cases such as skin damage exceeding six inches in any direction or three or more adjacent ribs. Major repairs need approved data and an FAA Form 337. Minor repairs can rely on acceptable data such as AC 43.13-1 and a logbook entry.

Getting the classification wrong is costly either way: paperwork you didn't need, or an aircraft returned to service on data that was never approved. This guide works from the regulation's own wording (14 CFR Part 43, eCFR current text) and from Chapter 2 of the FAA AMT General Handbook (FAA-H-8083-30B). You can query both, plus AC 43.13-1B and AC 43.13-2B, in the Kopik AC 43.13 base.

The three questions to ask before any job

The AMT General Handbook frames every maintenance action around three questions: what you are going to do, how the FAA classifies that work, and what documentation is needed to support it.

1. Repair or alteration? A repair returns the aircraft to its previous condition (the handbook's examples: replacing magnetos, an exhaust system, tires or brakes; even replacing an entire engine, if it is the one properly specified for that aircraft). An alteration always changes the aircraft from its previous state (winglets, new avionics, an engine not listed in the TCDS).
2. Major or minor? In the handbook's words, a major action is typically one that "might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness" and that is not done according to accepted practices or cannot be done by elementary operations. For examples, it sends you to 14 CFR part 1 and Part 43 Appendix A.
3. What data? Minor repairs and alterations need only acceptable data, "such as manufacturers' maintenance manuals or AC 43.13-1", recorded as a logbook entry. Major repairs and alterations require approved data, for example ADs, STCs, TCDS, DER-specific delegations and FAA-approved manufacturer service bulletins.

Airframe major repairs: what Appendix A actually lists

Appendix A, paragraph (b)(1), covers repairs "involving the strengthening, reinforcing, splicing, and manufacturing of primary structural members or their replacement, when replacement is by fabrication such as riveting or welding." The parts listed include box beams; monocoque or semimonocoque wings or control surfaces; wing stringers or chord members; spars and spar flanges; members of truss-type beams; thin sheet webs of beams; keel and chine members of hulls or floats; wing main ribs and compression members; wing or tail brace struts; engine mounts; fuselage longerons; members of the side truss, horizontal truss or bulkheads; main seat support braces and brackets; landing gear brace struts; axles; wheels; skis and ski pedestals; and control system parts such as columns, pedals, shafts, brackets or horns.

Then come the repair types that catch people out:

• Repairs involving the substitution of material.
• Repair of damaged areas in metal or plywood stressed covering exceeding six inches in any direction.
• Repair of portions of skin sheets by making additional seams, and the splicing of skin sheets.
• Repair of three or more adjacent wing or control surface ribs, or the leading edge between such ribs.
• Repair of fabric covering involving an area greater than that required to repair two adjacent ribs.
• Replacement of fabric on fabric-covered parts such as wings, fuselages, stabilizers and control surfaces.
• Repairing, including rebottoming, of removable or integral fuel and oil tanks.

Worked examples from the shop floor

AC 43.13-1B adds its own flags. For wing and tail ribs, repair schemes developed by the aircraft manufacturer are acceptable, "but any other methods of reinforcement are major repairs and require approved data" (paragraph 4-58c). For fabric, recovering or repairing with any type of fabric or coating other than the type used by the original manufacturer is considered a major alteration (paragraph 2-5). For sheet metal repairs to the airframe, the use of blind rivets must be authorized by the airframe manufacturer or approved by an FAA representative (paragraph 7-2j). On welded engine mounts, if the manufacturer stress-relieved the mount after welding, it should be re-stress-relieved after weld repairs.

Form 337: who signs, who gets copies

Part 43 Appendix B(a) requires each person performing a major repair or major alteration to execute FAA Form 337 at least in duplicate, give a signed copy to the aircraft owner, and forward a copy to the FAA Aircraft Registration Branch in Oklahoma City within 48 hours after approval for return to service. Note that the AMT General Handbook describes the copy as going to the local FSDO; the regulation text is the reference, so check the current eCFR.

• Item 3 is for FAA use: it is completed when there is no existing approved data and an inspector grants a field approval after reviewing your data. Often it stays blank because you used data already approved.
• Item 7 (approval for return to service) must be completed by the IA or an authorized individual from the repair station, according to the handbook.
• Item 8 describes the work and must reference the approved data used.
• A certificated repair station may instead use the customer's work order plus a signed maintenance release for major repairs made under a manual or specifications acceptable to the Administrator (Appendix B(b)).

Who may do what: A&P, IA and owner

• A&P mechanics perform maintenance, preventive maintenance and alterations as provided in Part 65 (§ 43.3(b)) and may approve return to service as provided there (§ 43.7(b)).
• Annual inspections: the AMT General Handbook cites 14 CFR 65.95(a)(2): "an IA must perform an annual inspection." The checklist is the same as for a 100-hour inspection; the difference is who may perform it and approve return to service.
• Supervised helpers may do work their supervising mechanic is authorized for, but this does not cover required inspections or "any inspection performed after a major repair or alteration" (§ 43.3(d)).
• Pilot-owners (except sport pilots, who have their own provision) may perform preventive maintenance on aircraft they own or operate that are not used under parts 121, 129 or 135 (§ 43.3(g)), limited to the Appendix A(c) list, provided it doesn't involve complex assembly operations. A private pilot may then approve that work for return to service (§ 43.7(f)).

Part 43 itself does not apply to aircraft holding an experimental airworthiness certificate, unless the FAA previously issued a different kind of airworthiness certificate for that aircraft (§ 43.1(b)).

A five-step decision routine

1. Write down precisely what you will do and on which part.
2. Check Appendix A (a) for alterations and (b) for repairs, line by line, including the size and count thresholds.
3. If it is on the list, identify the approved data (or plan a field approval) before cutting metal.
4. If it isn't, identify the acceptable data: manufacturer's manual first, then AC 43.13-1B where it applies.
5. Record it: logbook entry under § 43.9 for minor work; Form 337 under Appendix B for major work.

The base handles questions like "Does welding a crack in an engine mount count as a major repair I need to document on FAA Form 337?" or "How many adjacent wing ribs can I repair before it becomes a major repair?" with the citation. The regulation is on eCFR, 14 CFR Part 43.