aa.com is fairly clear
http://www.americanairlines.co.uk/i1...EuropeToUs.jsp
AA extends AAdvantage Platinum benefits to OW Sapphire members (BA Silver)
AAdvantage Executive PlatinumŽ, PlatinumŽ And GoldŽ Members
Two checked bags free of charge - maximum 23kgs / 50lbs each.
This applies to both US Domestic and Transatlantic flights.