Definition
An airport listed in an IFR flight plan as a place to divert to shortly after takeoff if the departure airport's weather is below landing minimums and the aircraft cannot safely return there. A takeoff alternate is required when the weather at the departure airport is below the operator's authorized landing minimums. The takeoff alternate must be within a specified distance from the departure airport (typically 1 hour at normal cruise speed in still air for two-engine aircraft, or 2 hours for aircraft with three or more engines, under Part 121/135 rules) and must have weather at or above its own alternate minimums at the estimated time of arrival.
Plain English
A nearby airport you plan to fly to right after takeoff if the weather at your departure airport is too poor to come back and land. You only need one when the airport you are leaving is below landing minimums.
Context Anchor
Seen in instrument departure planning, especially when checking takeoff minimums and deciding what to do if the aircraft has a problem soon after liftoff.
Derivation
“Alternate” comes from a root meaning “the other one.” In aviation, an alternate is not just any different airport; it is a specific backup airport chosen for a planned purpose.
Why Pilots Care
It ensures a viable landing option exists if an emergency occurs shortly after departure in marginal weather.
Intuition Check
Do not read “alternate” here as simply “another choice.” A takeoff alternate is a specific backup airport planned for the first part of the flight, in case returning to the departure airport is not safe or not allowed by the weather.
Example Sentence 1
Because visibility at the departure airport was below landing minimums, the dispatcher filed a takeoff alternate 40 miles away with clear skies.
Example Sentence 2
After an engine issue on climb-out, the pilot diverted to the takeoff alternate instead of attempting a return.