Originally Posted by newyorkgeorge

In that case there's more risk. If you're late due to mechanical problems AA would look at putting you on BA. If it's weather you're going to have a hard time other than being put on standby for the next AA flight to LHR, which would likely mean an overnight in MIA. I've noticed AA will have a cheaper (Main Cabin) fare but it often involves a tight connection. How long is your layover in MIA? I think the greater risk here is the MIA portion, if it's the same day. BNA doesn't get too impacted unless there's extreme weather.