A B757 FLT CREW EXPERIENCED A CABIN PRESSURIZATION PROBLEM IN CRUISE FLT. THEY RAN THE PROCEDURE; REGAINED CONTROL OF THE PRESSURIZATION SYSTEM; AND CONTINUED TO DEST.

Narrative

GND OPS AND CLBOUT WERE UNEVENTFUL WITH ONE EXCEPTION. PRIOR TO PUSHBACK; THE FLT ATTENDANT ASKED US TO TAKE A LOOK AT THE 3R DOOR BECAUSE; IN HER OPINION; THERE APPEARED TO BE A GAP THAT WAS LARGER THAN NORMAL. THE FO WENT BACK TO TAKE A LOOK AND SAID THAT IT APPEARED OK; AND THE DOOR WAS ARMED PROPERLY. ALL THE DOORS WERE SHOWING CLOSED; SO WE DECIDED IT WAS SAFE TO PROCEED. WE ASKED THE FLT ATTENDANT TO LET US KNOW IF IT WAS UNUSUALLY NOISY ONCE WE GOT AIRBORNE. WE DIDN'T NOTICE ANYTHING UNUSUAL IN THE PRESSURIZATION OF THE ACFT WHILE CLBING OUT. WE DIDN'T HAVE ANY EICAS MESSAGES OR NOTICE ANY STATUS CUE DISPLAYED EITHER. ABOUT AN HR INTO THE FLT AND AT FL330; WE GOT A CABIN ALT WARNING. WE COMPLIED WITH THE QRH PROCS WHILE REQUESTING AND RECEIVING CLRNC TO DSND TO 10000 FT. I CHKED THE CABIN ALT AND RATE OF CLB AND IT WAS ABOVE 10000 FT AND CLBING AT ABOUT 100-200 FPM. MY FIRST THOUGHT WAS THAT THE 3R DOOR WAS LEAKING; AND THAT WAS THE REASON FOR THE SLOW RATE OF CLB IN THE CABIN ALT. FROM A PHYSIOLOGICAL STANDPOINT; THERE WERE NO INDICATIONS THE CABIN WAS AT 10000 FT. KUDOS FOR THE SIMULATOR TRAINING THAT TEACHES TO START AN IMMEDIATE DSCNT. I CONTACTED THE FLT ATTENDANT AND INFORMED HIM THAT WE WERE DSNDING DUE TO THE CABIN ALT AND HE INFORMED ME THAT EVERYTHING APPEARED NORMAL IN THE BACK. VERY SOON AFTER WE STARTED THE DSCNT; THE CABIN ALT STABILIZED AT 0 FPM RATE OF CLB AND BY THE TIME WE WERE IN THE MID TWENTIES IT WAS DSNDING AGAIN. THE CABIN ALT LIGHT EXTINGUISHED AT AROUND 14000 FT AND THE CABIN CONTINUED TO DSND TO APPROX 4500 FT AT LEVELOFF. I DID NOT DECLARE AN EMER BECAUSE ATC DID NOT DELAY GRANTING OUR REQUEST FOR A LOWER ALT. WE DID TELL THEM WE WERE HAVING A CABIN PRESSURIZATION ISSUE AFTER THE FACT. BY THE TIME I REACHED THE STEP IN THE QRH THAT DEALS WITH THE CABIN ALT BEING UNCONTROLLABLE; THE CABIN RATE OF CLB HAD DROPPED TO 0 FPM; SO WE CONSIDERED IT CONTROLLABLE. AFTER CONSULTATION WITH THE MAINT COORDINATOR; DISPATCHER AND FLT ATTENDANT; WE DECIDED IT WAS SAFE TO CONTINUE TO ZZZ1. AT THAT POINT; THE ONLY ACFT ISSUE WAS THE OVERBOARD EXHAUST VALVE THAT SHOWED OPEN VIA A STATUS MESSAGE. THE FLT ATTENDANTS SAID THAT NO ONE IN THE BACK HAD MENTIONED OR APPEARED TO HAVE NOTICED THAT WE HAD DSNDED. THERE WERE NO COMMENTS FROM ANY PAX AS THEY DEPLANED RELATING TO THE DSCNT OR CABIN ALT. WHEN WE GOT TO THE GATE AT ZZZ1; WE WERE MET BY MAINT AND DESCRIBED THE EVENT. WE RELAYED THE SEQUENCE OF EVENTS FROM GND OPS TO LEVEL OFF AT ALT THROUGH DSCNT TO 10000 FT. WE FOLLOWED UP WITH THEM THE FOLLOWING DAY AND THEY SAID THAT THEY SUSPECTED A FAULT IN THE OVERBOARD EXHAUST VALVE OR CTLING RELAYS. THEY REPLACED THE OVERBOARD EXHAUST VALVE AND ASSOCIATED RELAYS. THEY ALSO FOUND AND FIXED SOME ISSUES WITH THE R PACK AND ASSOCIATED DUCTING.