Originally Posted by Upgraded!

Exactly, and I believe that would defeat the purpose; to my knowledge one cannot upgrade a BA flight with Avios if a TA is involved (unless that's changed). And I would't need one; AA will sell me this ticket with AA marketed/operated flights US-LHR, BA marketed/operated flights LHR-EU-LHR and IB marketed/BA operated flights LHR-US, which would be great except I cannot upgrade a BA/IB I fare with AA miles.

AA has a nice feature on its website allowing one to select AA flights, AA and OW flights and All Carriers' flights.