MD-82
Aircraft Equipment Problem Critical
General Declared Emergency
Aircraft
After leveling off at FL310 the 'cabin altitude' light illuminated and the aural warning sounded. [We] accomplished the immediate action items of 'Cabin Altitude Warning/Rapid Depressurization' checklist. Cabin altitude was over 10;000 FT and initially did not appear to be decreasing. Declared emergency and started emergency descent. During descent to 10;000 FT verified that cabin was not exceeding 14;000 FT. We did not deploy the cabin oxygen masks and they did not automatically deploy as cabin altitude remained less than 14;000 FT. Returned to our departure airport and accomplished an uneventful overweight landing. [It] appears that the automatic pressurization system failed.
[Narrative 2 contained no additional information.]
After experiencing an uncontrollable increase in cabin altitude; an MD-82 flight crew declared an emergency; performed an emergency descent to 10;000 MSL and returned to their departure airport where they completed an overweight but uneventful landing.