PRESSURIZATION PROB.

Narrative

AT LEVEL OFF FL290; EXPERIENCED CABIN PRESS LIGHT AND REQUESTED LOWER ALT. RECEIVED CLRNC TO FL270. INITIATED CHKLIST TO RESTORE CABIN PRESSURE. REQUESTED FURTHER CLRNC TO 11000 FT. RECEIVED CLRNC. IN SHORT ORDER TO 11000 FT MAY HAVE EXCEEDED INITIAL CLRNC TO FL270 PRIOR TO RECEIVING CLRNC TO 11000 FT. DID NOT DECLARE EMER. AUTOPLT INOP; COPLT WAS MANUALLY CTLING CABIN. PF WAS HAND FLYING ACFT AND COMS. ALT CTL MAY HAVE BEEN LESS THAN DESIRED OR ASSIGNED. SUPPLEMENTAL INFO FROM ACN 287952: AUTOPLT MADE A RATHER ABRUPT; UNCOMMANDED PITCH- UP SO THE CAPT HAND FLEW THE ACFT TO LEVEL OFF. ICING CONDITIONS HAD BEEN ENCOUNTERED; WING AND ENG ANTI-ICE EQUIP HAD BEEN TURNED ON AND THEN TURNED OFF AFTER EXITING ICING CONDITIONS. SHORTLY AFTER LEVEL OFF; THE MASTER WARNING LIGHTS AND CABIN PRESSURE ANNUNCIATOR LIGHT CAME ON. WE NOTED THE CABIN PRESSURE CLBING THROUGH 11000 FT AND CONTINUING TO RISE; SO WE DONNED OUR OXYGEN MASKS. ATLANTA ASKED HOW LOW WE NEEDED TO GO. THE CAPT REPLIED '11000 FT.' THE PAX OXYGEN MASKS DEPLOYED AT ABOUT 13000 FT CABIN ALT. I ACCOMPLISHED EMER CHKLIST PROCS. WE DETERMINED THAT THE R AIRCONDITIONING UNIT HAD OVERHEATED (POSSIBLY ASSOCIATED WITH EARLIER USE OF ANTI- ICE EQUIP) AND AUTOMATICALLY SHUT OFF DURING THE DSCNT; WE REGAINED CTL OF THE PRESSURIZATION THROUGH MANUAL CTL. THE FLT CONTINUED TO DEST AFTER THE AIRCONDITIONING UNIT AND PRESSURIZATION WERE DETERMINED TO BE OPERATING NORMALLY.