Originally Posted by
KARFA
AA flights on a BA ticket are upgradable with avios, but only from a very limited number of selling classes. Your AA flight would need to be in J, C, D, W, or Y selling classes in order to upgrade with avios.
I was not clear, I meant that BA will refuse to upgrade a BA leg because there is an AA segment in the itinerary. For example I wanted to UUA LHR-LAX from T to U/J but was declined because my ticket was GOT-LHR-LAX-SAN all ba legs except LAX-SAN that was AA.
Blamed it was a "married segment"