Selecting a destination alternate
 

Hi bodies.can any body answer that is there any regulation which specifies the min distance for an aerodrome to be selected as a destination alternate. In my company I have seen that while going to DUBAI if forcasted weather is fair then SHARJA is taken as an alternate, is it legal?

As far as I know, under parts 91 and 121 in the US, there's no minimum or maximum distance for the destination alternate. At my old airline, it'd be common to see a destination alternate that was 20nm away, with the same TAF. It was legal though, and there was ample chance to go elsewhere- provided you made the decision early enough.

There is no minimum distance from destination requirement but alternate itself is not required in certain conditions.
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)

It's a matter of sanity rather than regulation...

If the alternate airport is close enough to the destination that it will generally have the same weather, then it is not a good idea to use that airport as the alternate.

In my old operation the filed alternate was often not the one we were expected to use. There was some program used by dispatch for filing that was far beyond the understanding of pilots.

Still a common problem...