Some TATL flights on the AA/BA/AY/IB websites codeshare at comparable fares, but that's due to their joint venture. If you try to price out the same flights on the AS website, it becomes a pricey ticket. Looking at AY for next summer, the vig can be as much as $500 each way. The other problem with AS selling these flights, they don't have many codeshared connections once you get to the partner hub. On AS it's easy to book AY SEA/LAX/DFW-HEL, but nothing from HEL onward. If you look at the AY partner page on the AS website, they suggest connecting to Stockholm, amongst other places. The problem is you can't actually book that full trip on AS. You would have to book USA-HEL on the AS website, then use another site to book the connection from HEL onward. This makes the partner booking on AS somewhat worthless. I don't know about all airlines and codeshares on the AS website given I've not researched them, but for AY this is my observation.