How the AGL altitude changes with changed QNH? I'd like only to confirm or correct my intuition..
Airplane is maintaining certain FL with some QNH, its instruments are showing some AMSL. Now the airplane enters area with lower air pressure, but keeping the same set QNH. How the real AGL altitude changes?
My intuition is that altimeter is effectively showing certain pressure. If the atmospheric pressure drops (e.g. from 1013 to 990), to show the same measured pressure (altitude) the airplane has to descend. Then the airplane is having lower real AMSL than displayed on instruments.
Is my intuition correct?