I just ran into an unbelievable codeshare problem that made me think of the computer says no jokes.

I have booked HEL-LHR-SFO // DFW-JFK-HEL. HEL-LHR is AY, LHR-SFO is AA flight number, BA metal because AA doesn't fly international ex-SFO and because I need the AA segment to meet the status requirement for AAdvantage.

(DFW-JFK is AA and JFK-HEL is AA flight number, AY metal because the AY flight number would have cost me approx. €200. I don't understand how that is possible with the joint venture, where usually the price stays the same no matter whose flight number you use).

The booking has four booking references, one for AA and one for AY/Amadeus outbound and one for AY/Amadeus inbound. There is a 4th one, as well, issued by BA.

On the LHR-SFO flight I can either choose a seat by paying for it in advance, or choose it for free at check-in.

At T-36 I go to ay.com to check in. I use the AY reference. It automatically issues me a (bad) seat on the BA flight and a BP for both HEL-LHR and LHR-SFO. Calling AY doesn't help, they say they can't change the seat on the BA flight.

At T-24 for the LHR-SFO flight, I go to ba.com to change my seat. The BA booking reference works, but only allows me to reprint a boarding pass, not to change the seat since I've completed check-in. When I go to ba.com and insert the AY booking reference, it wants to redirect me to AY.com for check in. With the AA booking reference it finds no booking at all.

Calling BA, they tell me that with the BA booking reference, they can't see a ticket number and as far as they are concerned, I don't have a ticket and therefore can't check in (even if I already did). Then I give them the AY booking reference. They can see that I am checked in and want to redirect me to AY.com to change the seat. After I explain them that it doesn't work, they argue, then try for themselves and finally agree, then talk to a supervisor for a lengthy time, only to let me know that there is no way they can change the seat other than at the airport. Well, I know that at HEL they would give me the same story about not being able to change seats for a BA flight and at LHR, I would approach the desk maybe 1,5 hours before departure, so there aren't going to be any seats left.

They also tell me it's an AA flight. I tell them yes, the flight number is AA but the plane is BA. This doesn't help.

So they offered to cancel check-in completely.

I thought this is the worst suggestion to do and I would be completely crazy to agree and then thought, okay, let's go for it just to make this fun. It's still 18 hours to take-off so there's plenty of time to re-check-in if need be. So I let them cancel the check-in.

After this, I went to ba.com and typed in the BA booking reference. Now it worked and let me check in for the BA flight and choose a seat and print a BP. After this, I went to ay.com because I assumed I would need to re-check-in for the HEL-LHR as well. But on that site, it said I was already checked-in and everything seemed okay and I reprinted a BP for the AY flight + checked that also ay.com showed me the new seat for the BA flight to SFO. It did.

So in the end, it somehow worked. But for next time, I am going to follow these rules, whether there's a codeshare involved or not. Doesn't make the OW transfer a very smooth experience, though.

If you are on two separate carriers, (might only work on AY+BA combo):
- do not check in when the first flight is available for OLCI
- when the second flight is available for OLCI, go to the website of the operating carrier of this second flight AND make sure you have this airline's booking reference handy for OLCI
- do not accept if second airline tries to redirect you to first airline
- OLCI for second flight
- go to the website of the operating carrier of the first flight and OLCI