Definition
Changes made to an aircraft's design, structure, systems, or equipment that differ from its original certificated configuration. In FAA usage, alterations are classified as either major or minor, with major alterations requiring formal approval and documentation before the aircraft can return to service.
Plain English
Any change made to an aircraft that moves it away from how it was originally built and approved. Some changes are small and routine; others are significant enough that the FAA must approve them before the aircraft is flown again.
Context Anchor
Pilots encounter this term in maintenance records, airworthiness discussions, aircraft inspections, and FAA material about who may approve changes to an aircraft.
Derivation
From the Latin alter, meaning 'other' or 'different.' An alteration makes the aircraft different from the original approved design — which is why the FAA tracks and regulates these changes.
Why Pilots Care
Improper or undocumented alterations can invalidate the airworthiness certificate, create safety risks, and lead to regulatory violations during inspections or flights.
Intuition Check
Do not read alterations as just any casual change. In this FAA context, it means a change to the aircraft or installed equipment that may affect its approved condition, records, or legal status.
Example Sentence 1
The installation of the new avionics package was logged as a major alteration and required FAA Form 337 to be completed.
Example Sentence 2
The pilot checked the maintenance records to confirm no unapproved alterations had been performed on the flight controls.