Definition
An airport designated on an IFR flight plan to which a flight may proceed and land if a landing at the intended destination becomes inadvisable, typically due to weather below approach minimums or other operational issues. The selected airport must meet specific FAA weather and approach criteria at the estimated time of arrival.
Plain English
A backup airport listed in your flight plan in case you can't land where you originally planned.
Context Anchor
Seen when reviewing an instrument approach, checking weather requirements, and deciding whether a backup airport must be listed for the flight.
Derivation
From Latin alternatus, meaning 'one after the other.' In aviation it carries the sense of a second, prepared option held ready when the first cannot be used.
Why Pilots Care
Ensures a safe landing option exists when primary airport conditions are inadequate.
Intuition Check
Alternate does not mean just any other airport nearby. In this context, it means a planned backup airport that must be suitable for the aircraft, weather, fuel, and type of flight.
Example Sentence 1
Because the forecast at the destination showed possible low ceilings, the pilot filed an alternate fifty miles to the south.
Example Sentence 2
Reviewing the approach includes confirming whether an alternate airport is required.