If all of us can just upgrade our pressure altimeters into rad alt then we can scrap this QNH thing altogether.
Mmmm, so if I instruct one pilot to maintain 5000' on his radalt, and the other 6000' on his, are they going to enjoy the constant changing of the aircrafts attitude to follow the contours of the terrain beneath ?
And when the guy at 5000' is flying 1000' below them and triggers the radalt, are they going to do a zoom climb to ensure the 6000' based on the radalt is complied with ?
QNH is primarily used for terrain clearance, but there is also a secondary and important use in providing separation from other aircraft as part of an airspace system.