Originally Posted by
Time traveller
It would vary by the day of the week, but it was my understanding that JFK-LHR usually has the most availability as that route has the most number of flights amongst AA and BA TATL flights.
And just to add further confusion to the mix, I've been on the late arriving AA 91 (LHR-ORD, last flight) a couple times in J with about a 75% load. You may have to overnight in ORD though.