Originally Posted by
glenbrook
To get a handle on the error we need to know where and how the ping transmit/receive time was measured and the total round trip time.
Someone said earlier that the messages are sent in well-defined timeslots, so you wouldn't necessarily have to look at the round-trip delay, but the difference between the time the message was received from the aircraft and the 'ideal' start of the timeslot if the aircraft was directly below the satellite. That's assuming it's fairly well synchronized to the satellite, which you could determine by looking at previous flights that sent position reports.