Wouldn't the easy solution be to use two sets of letters for IATA coded flights for the same airline?
Something like "DL1234" and "DZ1234" for Delta?
I know a lot of the two-letter codes are claimed too, and I'm sure there must be some reason this wouldn't work OK, but it would seem like they they would each have at least one code left over from the various airlines they've acquired over the years?
If an American Airlines regional flight started with "TW1234" again, for example, I don't think it would break the world.
It almost certainly would completely break thousands of functions that have those magic letters hard coded into them in fortran, cobol, C or whatever. You might even find that clever people back in the 70s used other ways of representing those letters so you can't even search for them.
I've worked on codebases like this -- I've seen it take a team of engineers years to add a single digit to an ID number in a multi-million LOC mixed language codebase that was written in the 60s.
It's not that it can't be done, it's that it costs millions of dollars and takes years and you're never sure it's actually done because nobody has ever written a single test for the system and if you tried that would take years as well.
In prior roles, I've worked at 2 of the largest US airlines that have gone through mergers. There are lots of hard-coded letters in decades-old code that help identify what's mainline, regional, and OA (other airline). We're talking everything from reservations (booking) to revenue recognition (flight departure).
It would be no simple feat to upgrade the tech stack. Hell, some of the mergers are still lingering within the systems because airlines wanted to complete it quickly for the passengers. The backend, however, has band-aids all over the place.
And there is so much functional testing that needs to occur on systems boundaries. I'm just thinking of crazy things that happen often enough like luggage getting put on the wrong flight and shipped via another carrier via agreement.
I get the appeal (and the 60 years of accumulated technical skeletons, and the business and legal necessity) of keeping all of the airline’s segments coded as the same carrier and notionally able to connect to one another. I do wonder, though: in your scheme with a notional “DL” range and a notional “DZ” range, would it be feasible to partition the real-world flight networks in a way that keeps all the tickets as “same-carrier” according to the legacy logic?
That is, could you partition the flight network such that nobody has purchased or ever will purchase a single ticket that spans flights from both ranges? Assuming maybe that a significant number of “backbone” flights (e.g. between hubs) can themselves be “codeshared” between the new DL and DZ ranges. If so, how much new flight number space could you buy, considering the tradeoff between “codeshare all the new DL/DZ flights” and “free up the most new flight numbers”?
That's not such a great solution, it kicks the can down the road and it's super confusing to humans to have the same airline be represented different ways.
As a traveler, I already know the airline name because it's printed on my boarding pass, so I don't really care what two-letter prefix they use; to me it's just another part of the opaque handle they call a flight number.
It's common in Asia, with regional affiliates like the different AirAsia, LionAir, and VietJet companies having virtually identical branding but different flight prefixes.
I can confirm for AirAsia and Lion Group, and IIRC Ryanair also do this with their UK subsidiary with different flight prefixes and different aircraft registration numbers.
Something like "DL1234" and "DZ1234" for Delta?
I know a lot of the two-letter codes are claimed too, and I'm sure there must be some reason this wouldn't work OK, but it would seem like they they would each have at least one code left over from the various airlines they've acquired over the years?
If an American Airlines regional flight started with "TW1234" again, for example, I don't think it would break the world.