Flight Numbers - why have more than one?

[Dee747]

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 Can the flight not be published as BA711 and the callsign also be "Speedbird 711"?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

[Skipness One Echo]

They're not flight numbers, there's one flight number per airline on each flight, don't add codeshares as that just overcomplicates the question(!)
The BA123 will have a callsign used by ATC which may or may not be "Speedbird123" writtenas BAW123. However it may also have an aplha numeric random callsign like BAW1TC if the BA133 and BA123 are likely to be on the same frequency at the same time.

This is good practice but not universal as Emirates have a lot of similar sounding traffic in Dubai at the same time. I think the kick off was British Midland which had BMA1, BMA51, BMA81, BMA331 and BMA441 all in or around the Bovingdon stack in the first wave....

So it's not a benefit, more of a precaution. Most BA flights use the flight no as the callsign, most easyJet flights don't, however some do. Even some Virgin flights now carry a letter suffix on the *ATC callsign* for the same reason, i.e. VS901 / VIR901V.

[Dee747]

So basically it's belt and braces in case of ATC transmissions being misheard or misinterpreted with similar sounding flights in the same area at the same time? I can see the logic in that. Just seems random to those not in the industry.

Thanks for the explanation.

[DaveReidUK]

So basically it's belt and braces in case of ATC transmissions being misheard or misinterpreted with similar sounding flights in the same area at the same time? I can see the logic in that. Just seems random to those not in the industry.

Eurocontrol reportedly have a computer system that identifies potential conflicts between not only flight numbers of aircraft likely to be talking to the same centre at the same time, but also other possible sources of confusion such as frequencies, runway headings, etc.

[DVR7R]

Out of interest, who decides what the alpha numeric callsign will be?
Is it the airlines own system?

[DaveReidUK]

Out of interest, who decides what the alpha numeric callsign will be?
Is it the airlines own system?

Airlines are free to choose their own alphanumerics. Some, Lufthansa for example, appear to have a system that does it for them. Others, like BA, look like they have a bloke who sticks his finger in the air and makes one up (with the exception of SHT alphanumerics, which do follow a discernable pattern).

[Dee747]

look like they have a bloke who sticks his finger in the air and makes one up

That's precisely the reason for my OP. That's how it generally looks to the spotter/FR24-user/anorak. Though I always suspected there had to be a more rational explanation hiding under the surface.

[DVR7R]

Thank you DaveReidUK

[Skipness One Echo]

Only the legacy SHT callsigns are intuitive, "man with finger" wrote the new BHD and LBA ones.

[GT3]

Occasionally some are quite clever.

The BA to Seattle became BAW5EA a while back.