Boeing 757-200 (N938UW)

This aircraft was flying AA Flight #663 (PHX-KOA) today returned to PHX. It was just a hundred miles or so out over the Pacific when it descended rapidly and turned around. It flew back at an altitude of approx. 9,900ft almost the whole way back. Hmmm?

Oh, today is 20 Dec 2018.

Strange - seems like it could have been a pressurization issue maybe? Or is that stating the obvious. Was on the ground for 2.5 hours.

Yeah, I figure some kind of pressurization issue since it descended so rapidly and then stayed below 10,000ft for the rest of the flight. But it must not have been too serious since they headed for LAX at first, then made a right turn back to PHX. I'm guessing since PHX is a hub for Ameican they would have better support there. Anyway, sort of interesting.