There are some justifiable reasons for setting standard pressure on the second altimeter: should your flight altitude be close to the base of an airway/controlled airspace, which is designated as a flight level, because it could act as a valuable heads up. Similarly when flying using regional pressure (UK) then having the aerodrome QNH set on the second altimeter does a similar job when flying below the base of controlled airspace which is designated as an altitude. For those who land using QFE then having the aerodrome QNH set on the second altimeter is a common practice, ready for a go around and diversion.
But, once again we return to the possible folly, in the minds of QNH people, of fiddling about with altimeters at a critical point in the flight. QNH, QNH and only QNH is the normal standard of IFR pilots and also for those who regularly fly internationally. Outside of the UK and France QFE is rarely found. It was a common practice for commercial transport flights to land at one place using QNH and another using QFE, whatever was provided locally. This could happen many times on the same day and was a recipe for disaster. I can remember a number of tragedies with a considerable loss of life owing to the miss-setting of the altimeter by the pilots during the approach to land.
Last edited by Fl1ingfrog; 5th Aug 2020 at 09:51.