Guys,
You are right about c/s abbreviation- if you have a company designator you should never abbreviate the c/s!
With regards to the alpha numeric callsigns (eg BAW797b/BAW74PL etc..) these are used where timetable scheduling means that two(or more) similar callsigns are likely to be on the same frequency, usually in en-route sectors, at the same time in an attempt to prevent callsign confusion.
Crossair were one of the worst offenders regarding similar callsigns. CRX827, 837, 857, 867, and 887 all used to hit UK airspace at the same time in the same sector and non of the pilots bothered using their full c/s when replying to ATC instructions. I understand they spent several thousand pounds trying to sort out the problem and came up with...yes you guessed it alpha numeric callsigns!
As atcos, we can file a similar callsign report and then NATS then goes to the airline and asks them to change the callsign to one which is less likely to cause confusion.
Sorry Brum guys, but as long as the airlines keep putting on flights at the same time with similar callsigns (in your case BAW797B is so called instead of BAW1797 cos there is also BAW 1793 and at the same time), the alphanumerics are here to stay!!
[This message has been edited by atcomatic (edited 22 November 2000).]