Suitable and appropriate alternate aerodrome at which an aircraft would be able to land after experiencing an engine shutdown or other abnormal or emergency condition while en route in an ETOPS operation.
Since these en-route alternate aerodromes serve a different purpose than the destination alternate aerodrome special attention should be paid to fulfill the following:
• The landing distances required as specified in other OMs (e.g. AOM/OM-B) taking into account; wind and runway surface conditions, permit the aircraft to be stopped within the Landing Distance Available (LDA) as declared by the aerodrome authorities.
• The aerodrome services and facilities are adequate to permit the conduct of an instrument approach to the runway expected to be used while complying with the applicable aerodrome operating minima.
Source: ICAO Annex 6