FAA Form 337, Major Repair and Alteration, is the form on which major repairs and major alterations to a US-registered aircraft, engine, propeller or appliance are recorded under 14 CFR 43.9(d) and Appendix B to Part 43. The person who did the work gives a signed copy to the owner and sends a copy to the FAA within 48 hours of return to service.
Why it matters when licensing company data
A major repair or alteration is one that could appreciably affect weight, balance, structural strength, performance or other qualities affecting airworthiness, as defined in 14 CFR 1.1. A certificated repair station may instead record a major repair on the customer's work order and keep a duplicate for at least two years, so not every major repair produces a Form 337.
Each completed form ties a described piece of work to its approved data and to the person who approved it, which makes years of them a structured history of major work. Owners must keep copies for major alterations, and those records move with the aircraft when it is sold, so a repair station's archive often includes records that relate to customers' aircraft.
See the filled-out Form 337 example and records repair stations keep.
Example
A repair station installs an avionics upgrade that counts as a major alteration on a customer's aircraft. The technician completes Form 337 with the approved data, the inspector signs the approval for return to service, one copy goes to the owner and one to the FAA registry. Years later, when the station describes its archive for a data license, it separates its own work orders from owners' copies and asks which customers must consent before any form leaves the company.
Source
14 CFR Part 43, Appendix B (eCFR). Definition reviewed November 9, 2026 by Origin Data Partners.