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An alternate aerodrome is 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.
An alternate aerodrome must comply with the following conditions throughout the period for which it is nominated as an alternate aerodrome:
- The aerodrome must be open;
- The airfield condition (available runway length, strength, etc.) must be suitable for the safe operation of the aircraft type;
- The status of electronic equipment must be suitable to permit safe operation in the expected weather conditions;
- The weather conditions must be sufficient to permit safe operation of the aircraft.
The following information is taken from ICAO Annex 6, Chapter 4.
Alternate aerodromes include the following:
- 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.
- A take-off alternate aerodrome shall be selected and specified in the operational flight plan if the weather conditions at the aerodrome of departure are at or below the applicable aerodrome operating minima or it would not be possible to return to the aerodrome of departure for other reasons.
- The take-off alternate must be within a specified distance of the departure aerodrome.
- For an aerodrome to be selected as a take-off alternate the available information shall indicate that, at the estimated time of use, the conditions will be at or above the aerodrome operating minima for that operation.
- En-route alternate. An aerodrome at which an aircraft would be able to land after experiencing an abnormal or emergency condition while en route.
- ETOPS en-route alternate. A suitable and appropriate alternate aerodrome at which an aeroplane would be able to land after experiencing an engine shutdown or other abnormal or emergency condition while en route in an ETOPS operation.
- En-route alternate aerodromes, required for extended range operations by aeroplanes with two turbine power-units, shall be selected and specified in the operational and air traffic services (ATS) flight plans.
- 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.
- For a flight to be conducted in accordance with the instrument flight rules, at least one destination alternate aerodrome shall be selected and specified in the operational and ATS flight plans, unless:
- a) the duration of the flight and the meteorological conditions prevailing are such that there is reasonable certainty that, at the estimated time of arrival at the aerodrome of intended landing, and for a reasonable period before and after such time, the approach and landing may be made under visual meteorological conditions; or
- b) the aerodrome of intended landing is isolated and there is no suitable destination alternate aerodrome.
Note: The aerodrome from which a flight departs may also be an en-route or a destination alternate aerodrome for that flight.
(ICAO Annex 6: Operation of Aircraft, Chapter 4, Section 4.3.4)
ICAO Annex 6: Operation of Aircraft