An aerodrome to which an aircraft may proceed when it
becomes either impossible or inadvisable to proceed to or to land at the
aerodrome of intended landing where the necessary services and facilities are
available, where aircraft performance requirements can be met and which is
operational at the expected time of use.

Take-off alternate. An alternate aerodrome at which an aircraft would be able to
land should this become necessary shortly after take-off and it is not possible to
use the aerodrome of departure.

En-route alternate. An alternate aerodrome at which an aircraft would be able to
land in the event that a diversion becomes necessary while en route.

Destination alternate. An alternate aerodrome at which an aircraft would be able
to land should it become either impossible or inadvisable to land at the
aerodrome of intended landing