Handle same callsign, new flightplan

[AndyTWF]

• Aircraft stays connected, but files a new flightplan
• These aircraft should be force assigned a new squawk

[hazzas-99]

I will need to check for sure, but I also believe that even with a change of callsign and flightplan, if someone logs off and on again in a short amount of time it sometimes leaves them with the same squawk assignment.

[hazzas-99]

@AndyTWF just to say, I think this is still the case. Aircraft flies into EGNX as ANDY123 with squawk 7431. They disconnect, refile a new flightplan under the callsign GHAZA but forget to reset their squawk to 2000 before connecting. Me (as a controller using Mode C, in case that makes a difference) assigns them 7431 in their next clearance as it hasn't reassigned it!

Is that because the allocation method doesn't see there being a problem as long as ANDY123 has disconnected, since the squawk is effectively now available?