Originally Posted by
spacetracer
Folks...we can't trust to any ADS-B data from FR24.
For instance it shows around 80 kt everytime we are on the ground after landing.
Our today's flight: two landings: 10.42 and 11.00, the first landing is displayed with zero ALT and AS 79kt, the second- 1500 ft with 80 kt while on the ground. I should say the elevation of the helipads is almost the same(400 ft).
I could see no any accurate data on the FR24 and even location is wrong.
So it's better to keep that in mind when concluding the the last seconds of the flight discussed.
ADS-B data is sent from your aircraft, it is as accurate as your sensors. For example, if you're low to the ground and don't have good GPS reception, your position could be inaccurate.
To be logged by FR24, an ADS-B transmission has to be received by one of its receivers, and their coverage is not complete (and it also appears that messages drop out more in high-traffic areas). So if the last transmision FR24 receives from you is during your approach at 1500ft and 80 kts before your craft gets too low and loses radio contact, that is what it will display, because that is all it has. For the FR24 realtime tracking, there may also be programming that guesses where aircraft are when reception drops out intermittently; I expect that observed "impossible" flight maneouvres result from "bad guesses" during dropouts. And aircraft themselves are supposed to "guess" their positions between GPS updates when sending out ADS-B data.
In this case, we are looking at a completed flight, and (presumably) the exact ADS-B data as it was received from the aircraft; and here also, we know that we don't have complete coverage because the final few hundred feet down to impact altitude are missing from the data.
(I have also seen a study that suggests some ADS-B systems have hardware or software issues that could cause small errors in the data. It's always a good idea to cross-check if the data make sense.)