What Is Alternate Airport? Definition & Meaning in Aviation
An alternate airport is a backup airport where a flight can land if it cannot land at its destination.
In plain language
Flight plans must name an alternate when weather or other conditions make a diversion possible, and the aircraft must carry fuel to reach it.
Example
A flight to a fog-prone airport will often carry fuel for a nearby alternate airport.
Why it matters
The alternate is the plan B written into every flight plan. When your flight diverts, the alternate is usually where it lands, so it shapes how disruption plays out.