Generally it's easier to book a trip with legs on different carriers if they have a codeshare arrangement, because you can just do it as a single itinerary through one carrier's web site. Otherwise you often need a travel agent to be able to put together the itinerary (that's not strictly necessary though, just the way they make it work so no technical reason they couldn't just offer non codeshare flight numbers)
The other thing is airline points/status - sometimes you get no status points/miles on non-codeshare partner flight numbers but you do on the codeshare flight numbers.
If it's a connecting flight, and the incoming flight is running late, then the airline "sorts you out". Basically they know sboit your connection and make a plan.
I've been on a plane out of Heathrow that waited for a 30-min late incoming flight. I've also been on a late flight where my connection has been rebooked for me because we arrived late.
If you book "2 tickets" you're basically a no-show to the first flight, and you're on your own dealing with that airline.
I did that once - book connecting flights on two different tickets - and although I ended up actually making the connection (despite the first flight running 2-3 hours late), the experience was so nerve-racking I swore I’d never do that again. It helped that the flight I was connecting to ended up running late too.
The reason I did it was it was a personal side-trip (to see family) on an international work trip, and although my employer would let me mix work and personal travel on their booking (provided I reimbursed them for the cost of the personal portion), the bureaucracy involved had put me off going down that path.
> provided I reimbursed them for the cost of the personal portion
How does that work, given that the cost of the personal portion isn't independent of the rest of the booking?
I was just looking at a flight plan on kiwi.com that they could book for $900, with the individual legs costing $250, $350, and $500 if booked through the carriers.
They price two itineraries - one with the work part only, the other with both work and personal. They book the combined itinerary and then you reimburse them the differnce
I’m not familiar with Kiwi, but I noticed a comment thread about them on travel.stackexchange.com recently, discussing whether to describe them as “fraud” or just “using booking practices that subject the client to extreme risks”. Be sure to read the fine print on that booking!
The only problem with them is that they will search for and book flights with exactly the maximum luggage allowance that you specify, and they don't make this clear or really point out that you need to specify an amount of luggage corresponding to the amount you'll be taking with you.
They will also show you itineraries that result from booking separate legs of the flight separately, which I'm guessing is what you're referring to. That's not in the fine print; you cannot possibly avoid being made aware when that's happening.
You don't need to be on a codeshare for that to work though, it just needs to be on the same itinerary - the flight numbers can be on different airlines and still on the same itinerary.
Purely speculating, but I always assumed that the rationale for code share flight numbers must have been something technical, e.g. the airline code indicating which airline’s database a given record is located (ticket, bag tracking code etc).
It’s probably not strictly necessary anymore today (as you say, I’m pretty sure I’ve had a ticket across two carries without a codeshare number), but maybe it was at some point?
I don't know about "arbitrary" but most of my travel I book with something like Expedia ends up being split across carriers without using codeshare numbers. E.g. over Christmas I visited my parents in Australia and the domestic leg to Tokyo was a JL flight number, and international leg was a QF flight number, both on the same itinerary/using the same confirmation code.
A CRS/GDS locator (PNR, the 6-digit alphanumeric code often used to identify tickets, but really only points to a GDSs database entry) and a ticket are not the same thing, though. A PNR can include non-air travel segments like hotels and rental cars too, for example.
That's something very different from a single airline issuing a ticket for a complete itinerary, which importantly makes them responsible for getting you to your final destination in case of missed connections, checking your baggage through etc.
If you still have the confirmations or boarding passes, you could check for the three-digit numeric e-ticket number prefix, which defines which carrier actually issued the ticket.
JAL (JL) and Quantas (QF) are both members of Oneworld, so they can share itineraries (and things like frequent flyer status and fare class) in a single booking regardless of codeshare.
Isn't it entirely dependent on the airlines, what counts as one itinery? How could I contractually obligate them to something they didn't agree to be contractually obligated to?
(BTW: I've had multiairline itineraries many times. I think a lot of airlines are perfectly happy to do it because they can't fly domestic in that country and the domestic airline doesn't fly international. Also, there have been times when I haven't been able to, and I've been worried about it, and I got to the airport for manual checkin, and they've said "oh, i see you have an ongoing flight to such-and-such, do you want me to check you in for the whole journey?")
Nope, they can't, either the GDS allows booking it in which case it's already possible or the GDS doesn't allow booking it and then no app can do it. There are plenty services already which allows you to book the craziest itineraries. Like, ITA Matrix Powertools can construct a clickable link into Orbitz from ITA Matrix searches and it doesn't get crazier than that. There's Bookwithmatrix too.
I guess my question is, is it easier to upgrade the carrier website flight booking engines and mileage programs to deal with the original carrier flight numbers rather than upgrading all of the systems across the industry to deal with a larger name space for flight numbers universally?
The other thing is airline points/status - sometimes you get no status points/miles on non-codeshare partner flight numbers but you do on the codeshare flight numbers.