Fri Feb 15, 2019 1:48 pm
This is an old post but as I run an aircraft tracking system based in the UK (360Radar) I can shed some light on this.
The aircraft only transmits the ICAO hex code although if it's a GA aircraft it may transmit the registration as the callsign.
All flight tracking sites (FlightAware, FlightRadar24, 360Radar etc) need a way of relating the hex code to the aircraft details and for that we turn to the relevant national aircraft register (where published, not all countries make this public).
In the UK that's G-INFO but it's illegal to scrape it automatically so it relies upon volunteers to copy the data across when they see an otherwise unidentified aircraft.
Humans errors will be introduced so it's possible that someone looked up the wrong hex code and got the wrong registration or perhaps as was suggested the transponder was secondhand and transmitting the old registration as part of the callsign.
It could be that the transponder was programmed with the wrong hex code. There are quite a few aircraft floating around in the UK airspace with the completely invalid hex codes.
For example, during the week 000001 is transmitted by a USAF F15 whilst at weekends it can be seen being transmitted by a GA aircraft. If it ever ventures near to be I'll let the pilot know ! There are also several miscoded RAF aircraft that I've seen too as well as transponder that have been salvaged from now scrapped aircraft and not reprogrammed.
At 360Radar we take our registration data from PlaneBase which is also compiled by volunteers. In general there are very few mistakes in it and they seem to have a author -> edit -> publisher model where the information is checked and rechecked before going live.
That said, many of 360Radars subscribers are obsessive aviation geeks and don't hesitate to point out any errors and discrepancies which I then fix but only where I can corroborate the details with at least two sources. These are fairly few and fair between though.
FlightRadar24 users post updates on aircraft with missing details to the FR24 forums. How vigorously these are checked before being put into the database that sits behind FR24 I don't know.