Originally Posted by
DaveReidUK
Nothing so complicated.
The aircraft simply transmits either a Ground Position ADS-B message, which for obvious reasons doesn't need to contain an altitude, or an Airborne Position, which does.
So how does a 737-MAX 8 or a 738NG or any other late model aircraft know when to transmit via ADS-B that it has become airborne? And if it does, and gets it wrong at 93kts groundspeed, against what are all its subsequent pressure altitude reports calibrated?