Originally Posted by
RYFQB
In my experience, the personal/hobbyist ADS-B receivers will silently carry over data from a previous packet if it receives an incomplete packet. I often see only one parameter change when I observe an aircraft at the limit of my range, say altitude may be changing while lat/lon is fixed for a while.
What you are describing is of course a function of the software that's displaying the received data, not the receiver itself.
And it's not necessarily related to "incomplete packets".
Those analysing the FR24 data will have noted that every row in the table contains a complete set of values for lat/lon. altitude, track, groundspeed and VS. But that's not what actually happens - the aircraft
never sends all those parameters simultaneously as the DF17 squitter packet isn't long enough to accommodate them all.
Instead, they get sent in separate packets and FR24 simply carries over the last received values for those parameters that aren't part of a received packet. That's why, for example, the lat/lon values at 04:13:12 and 04:13:13 are identical, which is impossible unless we're talking about a helicopter or a vertical dive/climb with zero groundspeed.
So, essentially, the only values that can be taken at face value are those that have actually changed compared to the previous row in the table.
And even some of those are suspect - I have yet to see any explanation of the apparent 5g deceleration at 04:13:00 other than the timestamps being out of sync, GPS/NTP notwithstanding.