Definition
A change made to an aircraft's type design, structure, systems, or equipment that goes beyond routine maintenance or repair. Alterations are classified by the FAA as either major or minor, and major alterations require approved data and proper documentation (typically FAA Form 337) before the aircraft can return to service.
Plain English
A change to the aircraft itself — adding, removing, or modifying something so it is no longer exactly as the manufacturer built it. The FAA cares whether that change is small or significant, because significant changes need formal approval and paperwork.
Context Anchor
Pilots encounter this word in maintenance records, airworthiness discussions, aircraft logbooks, and FAA rules about who may make changes to an aircraft.
Derivation
From the Latin alter, meaning 'other.' To alter something is to make it 'other than' it was. In aviation, that 'other' state must still be airworthy, which is why the FAA regulates how alterations are made and recorded.
Why Pilots Care
Unauthorized or undocumented alterations can invalidate the airworthiness certificate, ground the aircraft, or create safety risks during flight.
Intuition Check
Do not read alteration as just any small change or adjustment. In this FAA context, it means a regulated change to the aircraft or its installed equipment that may affect whether the aircraft is approved and legal to fly.
Example Sentence 1
The installation of the new avionics package was a major alteration, so the mechanic completed FAA Form 337 and added the entry to the aircraft's permanent records.
Example Sentence 2
After the wingtip modification, the pilot confirmed the alteration was listed in the aircraft's maintenance records.