In Flight
I wonder why they keep using local & global air pressure-based altitude measurements instead of GPS. Is it just inertia, or does GPS have serious technical limitations when used in an airliner?I can understand relying on airspeed instead of GPS-measured groundspeed, because airspeed is important. But I can't think of a justification for not using true altitudes, especially during takeoff and landing. What happens if the pilots punch in a wrong number for the destination air pressure?