Originally Posted by
DCtoLondonFlyer
I am not sure, but I think you can then use your AA miles to redeem/upgrade on BA, just not on TATL itineraries. Maybe someone else can respond that knows for sure.
AA miles may be used to redeem on any BA flight EXCEPT between the US and Europe. So, for instance, LHR-YVR, LHR-MEX, LHR-GRU... (all tatl but not involving the US) are redeemable using AAdvantage miles.