I have found a great flight from LAX to Copenhagen/ return Stockholm to LAX --it's about $1000 on BA and American airlines and on Finnair it is less than $600 (carry-on only)--I have been reading some about code sharing where airlines will allow another airline to sell tickets on their planes-- but I am seeing flight numbers AY4013, AY5910, BA 775 and AY5459 on the 4 legs of this flight on the Finnair website....now my question is am I flying on FINNAIR or British airline planes???? Can anyone help with this info?? Thanks

What site are you looking at? AA, BA and Finnair belong to the same alliance. I checked the AA site and it indicates exactly which airline is operating the flights it offers, not that it matters much. When you buy your ticket, it includes all flights. The departure airport should issue boarding passes for each segment to your destination and your luggage should be checked through. Ditto on return. I can't get the Finnair site to search for a multi-destination route, perhaps because my computer is not located in the US. I am also handicapped by not knowing your travel dates, but for winter I can see extraordinarily cheap flights (considering the distance) on AA/BA combos without involving Finnair.

Looking at Finnair site LAX to Copenhagen on 8/25/19 and return from Stockholm to LAX on 9/23-- this site doesn't show which airline only the AY or BA flight numbers-- I think my concern is legroom and thinking BA and AA have better planes than Finnair which might mean more leg room for 10hr.+ flights..not sure if that is correct...also the BA and AA airlines have better reviews than Finnair on line...have lots of time to figure this out so thanks for all your help

<<I checked the AA site and it indicates exactly which airline is operating the flights it offers, not that it matters much >> It does matter which airline operates the flight, so you know which terminal to go to and which flight to look for and which gate to go to. The codeshare flight nos are also displayed, but there can be several codeshare flight nos for the same flight.

<<The departure airport should issue boarding passes>> Airports don't issue boarding passes, airlines do and on a connection, you always get checked in for both or all flights on that connection

<<I can't get the Finnair site to search for a multi-destination route, perhaps because my computer is not located in the US.>> What has the location of your computer have to do with what search options you can see. What matters is which Finnair site you land on. At the top of the flight search screen in the middle you will see a flag, if this is not the correct country (in this case it should be US), change the flag. Then you need to click on Other Options in order to see the Multiple Destination button

The Finnair site clearly shows in two places which airline is operating the flight. Not sure why the OP can't see it.
AY4013 is operated by AA - AA flight no is AA108 (777) into LHR T3
AY5910 is operated by BA - BA flight no is BA818 (A321) from LHR T5.
BA775 is operated by BA (A319) into LHR T5
AY5459 is operated by BA - the BA flight no is BA269 (A380) from LHR T5.

The AY website tells you the operating airline on the fares matrix itself where it shows you the flights times and there is a further link that you can click on that says Click to Open Details where again it tells you who the operating airline is.

Thanks Odin-- your information is just what I was looking for--also you listing the Terminals is of great help to make sure my Layover is long enough if I have to change terminals....knew someone on this site would be able to help as usual!!