Upvote:0
EDIT : Apparently what I showed you was not the best fit to what you requested. Best way if you cannot find where to eter yout British airways club number information it is to get in touch with American Airlines direclty ( call +44 (0)844 3699 899 if you are in the UK ) and check with them on how you can insert your club number when booking a flight with them.
I think you can find the whole procedure here that is appliable to your case. This procedure explains how you can use your AVIOS points in order to book an american airline ticket.
Upvote:3
Select "British Airways" under the "Program" dropdown, and input your British Airways Executive Club number into the "Frequent Flier Number" field.