Originally Posted by
FlightDetent
When discussing Mike Pence's 737 over-run at LGA, with the report an unexpected bias was found in the FR24 ADS-B data. Their recording showed a hard 0 for a few hundred yards where the actual aircraft was still floating above the pavement.
The connection I am making is what if the EK321's assumed late lift-off was also just an ADS-B mis-transmission, were they not airborne much sooner than indicated in the public domain? Bug or feature, to default for 'ground' below some small altitude. The FDM people already know.
I'm not familiar with the Pence incident but you are correct in that, given the reported QNH at DXB, ADS-B pressure altitude once airborne would have been negative until the aircraft reached approximately 150 ft AMSL (90 ft AAL).
FR24 always displays negative pressure altitudes as zero, and so should be treated with caution.
Edit: Just checked the Pence/Eastern thread, and the same FR24 issue applies there as a result of the QNH. In fact, it would appear that I mentioned it at the time.
