Originally Posted by
Uplinker
You cannot work out what an aircraft's IAS was from a groundspeed readout after the event, because you need to know the aircraft's TAS, so need to know the air density and temperature up there where the aircraft was at the time, as well as an accurate windspeed of the airmass you were in. None of this can be known from the ground.
Does ADSB not provide IAS?
Only suggesting it might because FlightRadar24 has a field for IAS but I'm too poor to afford gold membership and see it unlocked!