The operator shall select at least one destination alternate and specify it in the OFP for each IFR flight 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 no suitable alternate is available, in which case a point of no return (PNR) shall be determined.