If I'm not booked first class, I upgrade at the airport all the way since AA now charges for bags to JA. I would occasionally before when there was no extra baggage fee, just because it's nice. You have to upgrade each leg if you do it in the airport. Always do this if I'm flying domestic. I've never not been able to get a seat. It can't be done @ the airport coming back from JA unless that's changed. I make sure I'm flying first class on my return when I book (FF miles) for this reason so haven't checked for a while. It's nice for avoiding loong check in lines in MoBay.