Originally Posted by Pierre Argh
"more accurate, more relevant pressure setting"... of course QNH is more accurate, but "relevant"... only in certain circumstances? If you departed from the Isles of Scilly for, say, White Waltham, transitting below 3000ft what pressure setting would you use... QNH, which would be OK for about the first 20-30 miles but become increasingly less accurate as you progressed along your route. RPS has a built in safety factor, and is available in advance (so you could even obtain pressures for your entire trip before departure)
So's a chart with isobars and the QNH for your destination! In the very unlikely event of being unable to update your setting with real, observed QNHs due to comms failure, it's not hard to do rather better than the RPS as an estimate.
But that's beside the point -- if you want to write down RPSs for emergency purposes in advance of a flight, go ahead. Just don't ask
me to set it on my subscale when there's a perfectly good QNH available!
Originally Posted by Pierre Argh
It also means that in airspace populated by several airfields ... is flying on the same setting...
That would be "clutch QFE" then?
If a group of airfields in proximity want to use a common QNH for separation (e.g. like, er, London), let them pick an airfield (e.g. like, er, Heathrow) and use the QNH. Why use something irrelevant like RPS?