airsmiles
AlphaNumeric callsigns are not to make sense if the use of them is to work. Over 10 years ago, I worked with 'coded' AlphaNumeric callsigns. There are many Airlines operating the same routes, using 'predefined' flight numbers, ie, ABCxxx1 being the first flight, ABCxxx2 being the return. Now code a London-Paris for example 01LP and the return 02PL.......Multiple users of AlphaNumeric on a large network have the same idea. 0600 at LHR you have BAW01LP and 0605 you have AFR01LP, clipped transmittion and you should be seeing the point. It is all about ATC and callsign confliction as a previous poster said, so random works best. As long as the Airlines have a method of identifying the commercial flight number v the ATC call, the jobs a fish.
Now look at a base like STN for RYR, a lot of flights may leave on the same initial routing, for 100 miles.............. Forget other carrries in adjacent airspace, there is a problem.
Now for the carriers that attempt to corrupt XYZx370 to XYZ370 as my carrier did, the use of headings or levels is frowned on too.
MINE FIELD and random allocation is the key.
Bored