Originally Posted by
DaveReidUK
The fact that the ADS-B data being sent was subject to inertial drift doesn't necessarily imply that the crew didn't know exactly where they were. I haven't seen any suggestion that while they were flying the hold, prior to it all going quiet, they didn't have a working VOR/DME. (Well OK, the RNG DME could theoretically have been sending duff data, but Occam's Razor applies here).
It's analogous to an observer using ADS-B to monitor the height of an aircraft on approach, forgetting that it's displaying QNE whereas the crew will be seeing QNH-adjusted height on their altimeter.
ADS-B tells its own version of the truth.
Hi DaveReidUK,
I apologize for my wording. I assume the pilots were talking stock in the moving map as their source of position. My concern is whether the map may have shifted, putting the map position about 10nm north of the actual position. This would explain the decision to descend so rapidly and early landing configuration.
I think the ADS-B data is accurate to a couple of nm. I have looked at four flights on this airplane and can confirm its performance. It was disappointing that the IRS was not aligned at takeoff, with a 2000 meter offset evident.
Of course there is more information available to the investigation that should end any speculation. I have no other insight other than an apparent map shift to explain all the data we have released.