Originally Posted by omahajim

http://www.aircraftsimulators.com/73...s_placard.html

It's my understanding that aircraft pressurization is automated in some way, and related to current real aircraft altitude. By the time the a/c involved in this incident was at 4000ft, I believe the cabin altitude would have been much closer to this real altitude than 9000ft.

The web link shows above that below FL160, it appears that the cabin would have been pressurized to the air pressure at the landing airport.

I'm not an expert by any means, this is just the result of a little googling.