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Major vs minor repair and FAA Form 337: Part 43 Appendix A explained

Before any work on an FAA-registered aircraft, you need to know whether it is a repair or an alteration, major or minor, and what data and paperwork it requires. The assistant answers these questions from 14 CFR Part 43, its Appendices A and B, and the FAA AMT General Handbook.

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Answers are written by a language model solely from this base's documents, with numbered sources. They can be wrong and aren't legal, medical or financial advice: check the sources before any important decision.

Repair or alteration, major or minor

The AMT General Handbook explains that a repair returns the aircraft to its previous condition (replacing magnetos, an exhaust system, tires or brakes), while an alteration always changes it, such as installing winglets, new avionics or an engine not listed in the TCDS.

A major action is typically one that might appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics or other airworthiness qualities, and that is not done according to accepted practices or cannot be done by elementary operations.

Appendix A lists examples. Airframe major repairs include strengthening, reinforcing, splicing or fabricating primary members such as spars, spar flanges, wing ribs and compression members, engine mounts, fuselage longerons, landing gear brace struts, axles and wheels.

Acceptable data, approved data and field approvals

Minor repairs and alterations only need acceptable data, such as manufacturer maintenance manuals or AC 43.13-1, and can be recorded as a logbook entry.

Major repairs and alterations need approved data: AD notes, STCs, TCDS, DER-specific delegations or FAA-approved manufacturer service bulletins. Without approved data, the technician may request a field approval by completing Form 337 and submitting it to the local FSDO for review by an aviation safety inspector.

Frequently asked questions

Who receives the Form 337 after a major repair?

Under Appendix B of Part 43, the person performing the work executes Form 337 at least in duplicate, gives a signed copy to the owner and forwards a copy to the FAA Aircraft Registration Branch in Oklahoma City within 48 hours after approval for return to service.

Can a repair station use a work order instead of Form 337?

For major repairs made under a manual or specifications acceptable to the Administrator, a certificated repair station may use the customer's work order, give the owner a signed copy and a maintenance release, and keep a duplicate for at least two years.

What can a pilot owner do without a mechanic?

Section 43.3(g) lets a pilot certificate holder (other than a sport pilot) perform preventive maintenance on an aircraft they own or operate that is not used under Part 121, 129 or 135. The allowed tasks in Appendix A include tire removal and repair, servicing wheel bearings, replacing defective safety wire or cotter keys, and replacing safety belts, provided there are no complex assembly operations.

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