(i)  
1 hour flying time at an OEI cruising speed according to the AFM in still air standard conditions based on the actual take-off mass; or

(ii)  
the ETOPS diversion time approved in accordance with SPA.ETOPS, subject to any MEL restriction, up to a maximum of 2 hours, at the OEI cruising speed according to the AFM in still air standard conditions based on the actual take-off mass; 

(2)  
for three and four-engined aeroplanes, 2 hours flying time at the OEI cruising speed according to the AFM in still air standard conditions based on the actual take-off mass.

If the AFM does not contain an OEI cruising speed, the speed to be used for calculation shall be that which is achieved with the remaining engine(s) set at maximum continuous power.
(b)  
The operator shall select at least one destination alternate aerodrome for each instrument flight rules (IFR) flight unless the destination aerodrome is an isolated aerodrome or:

(1)  
the duration of the planned flight from take-off to landing or, in the event of in-flight replanning in accordance with CAT.OP.MPA.150(d), the remaining flying time to destination does not exceed 6 hours; and

(2)  
two separate runways are available and usable at the destination aerodrome and the appropriate weather reports and/or forecasts for the destination aerodrome indicate that, for the period from 1 hour before until 1 hour after the expected time of arrival at the destination aerodrome, the ceiling will be at least 2 000 ft or circling height +500 ft, whichever is greater, and the ground visibility will be at least 5 km.

(c)  
The operator shall select two destination alternate aerodromes when:

(1)  
the appropriate weather reports and/or forecasts for the destination aerodrome indicate that during a period commencing 1 hour before and ending 1 hour after the estimated time of arrival, the weather conditions will be below the applicable planning minima; or

(2)  
no meteorological information is available.

(d)  
The operator shall specify any required alternate aerodrome(s) in the operational flight plan.

CAT.OP.MPA.181 Selection of aerodromes and operating sites — helicopters
(a)  
For flights under instrument meteorological conditions (IMC), the commander shall select a take-off alternate aerodrome within 1 hour flying time at normal cruising speed if it would not be possible to return to the site of departure due to meteorological reasons.

(b)  
For IFR flights or when flying under VFR and navigating by means other than by reference to visual landmarks, the commander shall specify at least one destination alternate aerodrome in the operational flight plan unless:

(1)  
the destination is a coastal aerodrome and the helicopter is routing from offshore; 
　
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本文鏈接地址：Annexes to the draft Commission Regulation on ‘Air Operations - OPS’(84)