There's a "Terraces" lounge wich is open "3 hrs before departure".
http://www.oneworld.com/ffp/lounge-access/
It is listed as a "3rd Party Lounge", so AA access is not likely.
http://www.britishairways.com/travel...lic/en_gb#saac
Aside from that, opening time might not align with many AA flights.