Rt Hon Jim Hacker MP
Very good point. I never realized that actually. I always preset the destination airport QNH early during the flight to minimize this kind of mistake. At least when approaching the TL and ATC gives us the QNH, I know it will be close to the one I inserted earlier and it’s unlikely to set a wrong QNH of 10hpa. I guess a crosscheck with the RA is the last line of defense assuming the ground is relatively flat below. But just to confirm: If airport QNH is 1013 but the crew set by mistake QNH 1003, they will fly 300 feet too high and not too low.