Originally Posted by
Nemrytter
Nor does it exclude the possibility that, as with most other accidents, the Flightradar data is unreliable.
This might be a good opportunity to put this canard to rest.
FR24 data (and that from FlightAware, etc) is indeed unreliable, but only if you fail to understand its limitations. Don't forget that ADS-B in the cornerstone of many nations' (including the USA's) future ATM strategy, so it's got to have something going for it.
Yes, it was never designed for accident investigation purposes, but that's not to say that it's incapable of at least providing a pointer to what happened (though obviously not how or why). Nowadays it's not uncommon to see ADS-B GE plots in AIBs' accident investigation reports.
There are a number of reasons why FR24 needs to be treated with caution, some apparent in the Lion Air data.
Firstly there are still a handful of airliners with inertial-, rather than GPS-derived ADS-B (but that clearly doesn't apply here).
Secondly, because data is typically captured from multiple receivers for a single flight, timing issues arise. Those are readily apparent in the Lion Air data - most, if not all, of the "outliers" in the graphs we have seen in this thread are actually data which is genuine, but which is displayed in the wrong position in the timeseries.
Thirdly, and again it's obvious in the data, is the fact that FR24 typically displays both position and velocity data as if they have been received simultaneously (i.e. with the same timestamp), which isn't how ADS-B works. So, for example, a lat/lon value that hasn't changed between successive records with different timestamps doesn't mean we are looking at a helicopter, the coordinates have simply been copied over from the last genuine position transmission.
So, for example, if you look carefully at this GE plot you can see instances of these issues, which I'm still working on resolving, but to suggest that it therefore bears no relation to what actually happened is, I suggest, being somewhat perverse:
