flyme273:
A more reasonable pilot would oblige ATC and accept an extra 1,000 ft
Yes, lots of pilots would - including piperboy, who asked the question in the first place. But the point is, can ATC give that clearance to climb? You have (in piperboy's example) two aircraft on reciprocal headings heading for the same NDB, one climbing from 2000 to 4000, the other descending from FL250 or some such to 3000ft, and with a closing speed of perhaps 6 miles a minute. MATS Part 1 says that the lateral separation standard between aircraft on reciprocal tracks is 40nm, and also that "separation based on DME is not to be used when aircraft are within 15 miles of the overhead of the facility". That means that the vertical separation (light aircraft level at 4000, inbound CAT level at 3000) must be achieved, at the very least, before either aircraft gets within 20nm of Dundee.
From a higher altitude the commercial can expedite descent i.e. use speed brakes, on the outbound heading to be level per procedure at the turn.
You seem to be suggesting that the CAT inbound can descend below the level of something in the hold while descending outbound. SCAREEEEE!
If this became a sticky situation ATC would give the intruder priority.
Well, no actually. Other way round. If the controller had any doubt about the "intruder"'s ability to get to 4000 in time to achieve vertical separation from the CAT inbound, he would tell the "intruder" to remain VMC, give him a Basic Service and tell him to remain clear of the approach and report at a specified point. Otherwise he'd have to limit the intruder to 3000ft and the CAT inbound to 4000ft in the hold, and the CAT would be going round and round there till the light aircraft was on short final to land.
I never suggested flying below MSA.
So what was that "direct to D4 Garmin approach" thing then?
NS