It can't be done. AA upgrade instruments can only be used on AA marketed and operated flights.
Some BA and IB flights can be upgraded with AA miles, but only if they are in the most expensive fare classes. - e.g. Y or B to World Traveller Plus (Premium Economy), or W to Club World, or CW C, J, D or R to First (yes, only one class of service for an upgrade, and there are four classes of service including WT+). See
here. Also in the FAQ with links to FT threads.
Originally Posted by
blaknail
Are you able to use 500 Mile upgrades on AA flights booked other than through AA?
I am thinking of booking an itinerary on BA which includes an AA connecting flight; if I were to do this, can I request upgrades, and if so, how would I do it.
Sorry if this is a stupid question!