Don't know about that one, 2 sheds, it's a long time since I penetrated a MATZ. However, judging by the posts, things might have changed, in which case I am out of date (I'm not flying in the UK at the moment). But, if my memory serves me well, which it probably does not, QFE was only ever used for circuit traffic. Airfield QNH was used for transitting, and having transitted, RPS was reset.
For a while, I remember the RAF decided not to use QFE. New man at the top, I believe. During that time I always asked for, and was given, QFE. After a while there was a new new man at the top, and common sense prevailed once more. It makes life easier, believe me.
Originally Posted by Chilli Monster
Working on the basis that a) the UK is not a large country (if the pressure difference is that big you wouldn't be flying); and b) you're going to have to call an ATC unit for that regional pressure; then why not dial up a nearby ATIS and use that airports QNH? Might also have the added benefit of not busting CAS when the lower level is defined as an Altitude. (RPS in this situation having the effect of putting you inside CAS when you think you're outside).
I agree totally, Chilli, in that the UK is not a large country - could not disagree with you less on that one. However, it is still big enough for a depression to constitute a potential danger if flying into it; and it is still big enough to have areas remote enough and wild enough to be out of VHF coverage. Put those together, and I cannot recommend too strongly that you use the correct altimeter setting. You might have the option of not flying in those circumstances, but you would need to be pretty convincing to persuade an employer or a client.
Please allow me to try another tack: we are talking here about flight safety, in particular being able to ensure you are flying at a safe altitude over a remote area.
The greatest difference I can remember between airfield and regional pressures was equivalent to over 500ft. Obviously, a depression was approaching, but flying continued unabated, without any undue problem. If I were to fly over high ground, with RPS set, in my example that would give me an extra 500ft of safety margin, and I would have that extra margin for the next hour. Clever people work out this pressure for me, and I am grateful to them for the service.
On the other hand, you would presumably set airfield QNH and set off into an area of lower pressure. Immediately, your altimeter starts overreading, and your safety margin is reduced. Not by much, I grant you, but by a finite amount, while mine has increased. And how often are you going to update your setting, or more importantly, just how, if you lose VHF coverage?
Safe flying.