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. Alternate aerodromes may be designated as Take-off , En-route, or Destination alternates.
ICAO defines each of these as follows:
🟢 Take-off alternate – An alternate aerodrome at which an aircraft can land should this become necessary shortly after take-off and it is not possible to use the aerodrome of departure.
🟢 En-route alternate – An aerodrome at which an aircraft would be able to land after experiencing an abnormal or emergency condition while en route.
🟢 Destination alternate – An alternate aerodrome to which an aircraft may proceed should it become either impossible or inadvisable to land at the aerodrome of intended landing.
The aerodrome from which a flight departs may also be an en-route or a destination alternate aerodrome for that flight.
REFERENCES
ICAO Annex 2
