Originally Posted by
DaveReidUK
The aircraft didn't have GPS when it flew for CityJet, and I'd be surprised if it had been retrofitted, so the ADS-B position reports will be from an inertial source.
That's supported by the fact that the coordinates sent as it turned onto the runway at Viru Viru were offset by approximately 1 nm SSE, so it's likely that at least that much error will apply to the subsequent ADS-B track.
Are you sure? I thought ADS-B positions had to be satellite based.
From a Boeing article:
Navigation satellites send precise timing information that allows airplanes equipped with global navigation satellite system (GNSS) or GPS receivers to determine their own position and velocity. Airplanes equipped with ADS-B out broadcast precise position and velocity to ground ADS-B receivers and to other airplanes via a digital datalink (1090 megahertz) along with other data, such as the airplane’s flight number and emergency status.
http://www.boeing.com/commercial/aer..._article02.pdf
From an FAA page on ADS-B installations:
An ADS-B Out transmitter alone will not be sufficient to meet the requirements outlined in 14 CFR 91.227. To comply with the requirements for the ADS-B Rule, the aircraft must be equipped with a Version 2 ADS-B Out transmitter and a compatible GPS Position Source.
https://www.faa.gov/nextgen/equipadsb/installing/
I realize that this wasn't a Boeing flown under FAA rules but I've flown with legacy airliner installations where the ADS-B and TCAS had GPS but the FMS did not.