Definition
A repair or alteration to an aircraft, engine, propeller, or appliance that, if improperly done, could appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness, or that is not done according to accepted practices or cannot be done by elementary operations. Major repairs and alterations must be performed by appropriately rated personnel and documented on FAA Form 337, Major Repair and Alteration.
Plain English
A repair or change to the aircraft that is significant enough that, if done wrong, it could make the aircraft unsafe to fly. Because the stakes are high, only properly qualified people can do the work, and it has to be recorded on a specific FAA form.
Context Anchor
Pilots encounter this term when reviewing aircraft maintenance records, approving work on an aircraft they own or rent, or checking whether an aircraft is legal to fly after significant maintenance.
Derivation
‘Major’ comes from Latin maior, meaning ‘greater.’ In this context, it flags work whose consequences are greater — significant enough to affect airworthiness — as distinct from minor work that does not.
Why Pilots Care
It ensures that substantial work is properly documented and approved, preserving the aircraft's legal airworthiness and flight safety.
Intuition Check
Major does not just mean expensive or time-consuming here. In FAA use, it means the work could significantly affect the aircraft’s safety, performance, or flight characteristics.
Example Sentence 1
Replacing a wing spar is a major repair, so it had to be performed by a certificated repair station and recorded on FAA Form 337.
Example Sentence 2
Before returning the aircraft to service, the owner verified that all major repair and alteration entries were properly approved and logged.