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.
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.
A Take-off alternate aerodrome shall be located within the following distance from the aerodrome of departure:
•Aircraft having 2 engines: Not more than a distance equivalent to a flight time of 1 HR at the single-engine cruise speed; and
•Aircraft having 3 or more engines: Not more than a distance equivalent to a flight time of 2 HRs at the one-engine inoperative cruise
Source: EU-OPS