Genuine query which has puzzled me for years -
Why are multiple flight numbers assigned to certain flights? Now I'm not talking codeshares here - those are clear enough. I'm referring to a flight having several different callsigns/flight codes issued by the operator.
For example - in the good old days way back the BA shuttles inbound to Belfast used to have a callsign of "Shuttle 4 Alpha/Bravo/Charlie/etc" with the Heathrow bound ones being "Shuttle 5 A/B/C/etc". The actual flight numbers were BA9999 where the 9999 differed per flight. Same idea for all the other Shuttle destinations.
Today I'm tracking my daughter's flight from ZRH to LHR which is BA711, but it also comes up, and is displayed as, BAW5ZL on Flightradar24. Why have these two? Can the flight not be published as BA711 and the callsign also be "Speedbird 711"? What benefits are derived from the two code system, and who benefits? I'd guess ATC wouldn't have any difficulty just using "Speedbird 711". Interestingly the BA712 also now en route LHR to ZRH doesn't appear to have any alternative at all!! Curiouser and curiouser.
Similar with most airlines of course, not just BA. See flybe and easyJet flight numbers and callsigns.
Many thanks in advance for your responses
