Originally Posted by
SpringHeeledJack
Talking of flight numbers, whilst looking at various flights at various times these last weeks, I've noticed that there seems to be a reasonable proportion of them flying between point 'A' and 'B', but the flight tracker lists them as from/to other airports completely different to the route shown. These aren't 4-digit special flights btw.
Is it that flight numbers have been re-allocated and the system still has them in the previous iteration ?
Yes.
The flight trackers always struggle in April and November of every year, when the airlines switch between Summer and Winter schedules.
The reason is that, while the trackers pick up the ATC callsign for a flight, the route is derived by converting the callsign into the IATA flight number. That works fine for airlines that use wholly numeric callsigns (for example US carriers), but most major European carriers use alphanumeric callsigns which typically change every season for a given flight number. To make matters worse, the new alphanumeric callsign for a particular flight number may have been used in the past for a completely different flight, so the conversion that the flight trackers are using may be out-of-date.
For example, Lufthansa has used DLH1LA in the past for LH3383 (Heathrow-Dusseldorf) and then subsequently for LH2477 (Heathrow-Munich).