Definition
An airport at which an aircraft may land if a landing at the intended airport becomes inadvisable. Under instrument flight rules, an alternate airport must be filed in the flight plan when weather conditions at the destination are forecast to be below specified minimums, and the alternate must itself meet weather and approach criteria established by regulation.
Plain English
A backup airport you plan to fly to if you can't land where you originally intended. On instrument flight plans, you're often required to name one in advance, and it has to meet certain weather standards so you know it will actually be usable when you get there.
Context Anchor
You will see this term in flight planning, especially when weather, runway closures, fuel planning, or instrument flight rules make a backup landing airport important.
Derivation
From the Latin alternare, meaning 'to do by turns.' An alternate is the 'other choice' you turn to when the first one isn't workable. The aviation use keeps that everyday sense — the second option held in reserve.
Why Pilots Care
Required for most IFR flights when destination weather is marginal; ensures a safe landing option remains available.
Intuition Check
Do not read “alternate airport” as just any airport nearby. In aviation, it means a backup airport considered in advance for use if the planned destination is not a good option.
Example Sentence 1
With marginal weather forecast at the destination, the pilot filed an alternate airport thirty miles to the south where conditions were expected to remain well above minimums.
Example Sentence 2
Because the destination forecast showed low ceilings, the crew added a suitable alternate airport with better weather to the flight plan.