Alphanumeric Callsigns

[Localiser Green]

Just how do airlines like British Airways, bmi and others come up with their Alphanumeric Callsigns? OK I know it's a real "spotter question", but I just like to know where the planes I hear on my scanner are going, and if indeed there is any way to work it out.

I haven't been able to find any source (on the net at least) of a directory or listing of these callsigns. Presumably they must be assigned reasonably well in advance for someone to be able to construct a database?

Finally what is the purpose of the alphanumeric callsign, why can't the flight number simply be used like most carriers? Thanks.

[chiglet]

Several years ago, BAW had "bounce" flights.
EG, Paris-Brum-Glasgow.
The LFPG-EGBB leg was BAWxxx. The EGBB-EGPF leg was BAWxxxD [for Domestic}
Then they [BAW] started "Intelligent" callsigns...BAW34AM inbound Amsterdam, 44G, inbound Glasgow, but 72YZ inbound Brussels????
Short answer is "some" make sense, others don't :eek:
we aim to please, it keeps the cleaners happy

[Gonzo]

Localiser Green.

Often you'll find BA's alphanumerics were thought up because of the original flight number conflicting with a similar callsign somwhere along it's route.

ie. BAW482 and BAW462 depart LHR within 10 mins of eachother usually, and last year the 482 was changed to 48LB

Gonzo