Originally Posted by
Vengabus
Thank you for the replies. I will be using BA-earned miles and transferring them to AA to make the booking. The reason for asking was that the booking I am looking at has 3 legs and only the first has First class, whereas the others will be business class only. I was hoping to use miles book business for all and then upgrade the first leg to first, subject to availability. But if that is not possible due to the booking being made with miles in the first place, then I will just book First for all and take the hit that it won't be available on 2 of the legs.
What you're trying to do is not possible. You cannot upgrade an award flight booked with avios (or AA miles) with more avios (or AA miles).
And as noted above, it is not possible to just transfer avios to AA, if that is what you meant. You can book AA flights directly with avios, but you cannot transfer avios to AA.