Note that the Flightradar24 data we are being shown above are from the actual ADS-B outputs from the plane.
https://twitter.com/flightradar24/st...840256/photo/1
The times and positions are as broadcast from the a/c. However, the time data is actually given to millisecond precision (not just to the second).
In that last minute up until 23:12:04Z (when the data stopped being able to be collected) the plane was flying in a straight line at about 32000 ft, at about 480 knots, in a NW bearing.
Thus we can get pretty accurate estimates of the speed data by calculating across several successive data points instead of using just one and the next one. Also use the milliseconds. This seems to show a sudden slow down at the end of the minute: down to say 300 knots.
I will publish the calculations when I get a moment if no-one else does first.
Note also that there is apparently some separate radar data gathered for a little while after 23:12.