Narrative:

We were above 10000 ft MSL when I; the PF; began to notice the flight deck getting warm. I looked up to verify position of the temperature control valves and saw that the left duct pressure was reading approximately 10 psi and the right duct pressure reading approximately 45 psi. I brought this to the attention of the captain. We were above FL180 when the purser called the flight deck to inform us that the cabin was warm. The captain relayed that information to me; and I told him that I have the control valves full cold. We discussed amongst ourselves that the aircraft had a history of these packs putting out warm air and about duct pressure split. Upon leveling at FL330; the captain was in the process of sending a message about the duct pressure when he looked up and saw the cabin altitude of 9000 ft and climbing. He said the cabin is climbing through 9000 ft and he immediately radioed ATC for a lower altitude stating that we have a pressurization problem. After that the cabin altitude warning horn sounded; I silenced it; and the captain started the intermittent warning horn/in-flight cabin altitude/rapid depressurization qrc of which we performed our memory items and ran the rest of the qrc. During this ATC gave us FL250; and we descended at 3000 FPM in the hopes that we would catch the cabin and possibly regain control. Center then gave us FL210 and finally 16000 ft. Once we went to manual AC (according to the qrc) the cabin rate indicator immediately went to a 2500 FPM descent and leaving FL210 we noticed the cabin altitude now below 10000 ft. At this time we informed ATC that we have recaptured our pressurization and that it was holding and that we would like to level off at FL190 at which we did do. Then we took off our masks. We knew that the rubber jungle deployed as the cabin altitude did reach 15000 ft. We do not recall seeing an autofail light. Also the standby controller never took over as the first green light I saw was the manual light. Once we did level off at FL190; center asked us what our intentions were. The captain discussed with me that our pressurization is under control and considered to proceed to destination. At which time; I plugged in our new cruise altitude of FL190 into the FMC and reviewed the progress page to see the fuel we would land at (6.2) and said that I was comfortable with that decision. After we have stated our intentions to ATC; the captain talked to the purser; dispatch and maintenance. Once we got handed off to center we were given a crossing restr at 11000 ft. We proceeded with the clearance. I proceeded to get the ATIS and landing data for our arrival as the captain was still with dispatch and maintenance. When he came back; I informed him of our new altitude assignment and of current WX and landing information. I asked him if the purser saw any abnormalities; he said no; and we proceeded to run the approach/descent checklist and set up for our arrival. Unfortunately; we forgot the definition of 'manual' and neglected to adjust the outflow valve for the descent. The cabin started to bump and we noticed that the cabin altitude was below 'SL.' I immediately adjusted the outflow valve (over correcting) at which the cabin began to climb between 1500-2500 FPM. I asked the captain to finish with the irregular procedure for autofail light/unscheduled pressurization. Once he stated standby mode on the controller; the cabin regained control and we proceeded to land without further incident. Once at the gate; the cust service rep came on board to inform us that 2-3 passenger were complaining about discomfort in their ears. Hindsight; I think we should have leveled off at a lower altitude on our way to our cruise altitude of FL330 and spoke to maintenance earlier. Secondly; actually take out the aircraft log history and review it (because I thought that the split duct was previously reported) when in fact it was the APU duct putting out low pressure write-up that I was referencing.

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Original NASA ASRS Text

Title: B737 FLT CREW REPORTS CABIN ALTITUDE WARNING AT FL330 WITH CABIN ALTITUDE EXCEEDING 15000 FEET BEFORE MANUAL CONTROL OF THE CABIN IS REGAINED. FLIGHT CONTINUES TO DESTINATION AT FL190.

Narrative: WE WERE ABOVE 10000 FT MSL WHEN I; THE PF; BEGAN TO NOTICE THE FLT DECK GETTING WARM. I LOOKED UP TO VERIFY POS OF THE TEMP CTL VALVES AND SAW THAT THE L DUCT PRESSURE WAS READING APPROX 10 PSI AND THE R DUCT PRESSURE READING APPROX 45 PSI. I BROUGHT THIS TO THE ATTN OF THE CAPT. WE WERE ABOVE FL180 WHEN THE PURSER CALLED THE FLT DECK TO INFORM US THAT THE CABIN WAS WARM. THE CAPT RELAYED THAT INFO TO ME; AND I TOLD HIM THAT I HAVE THE CTL VALVES FULL COLD. WE DISCUSSED AMONGST OURSELVES THAT THE ACFT HAD A HISTORY OF THESE PACKS PUTTING OUT WARM AIR AND ABOUT DUCT PRESSURE SPLIT. UPON LEVELING AT FL330; THE CAPT WAS IN THE PROCESS OF SENDING A MESSAGE ABOUT THE DUCT PRESSURE WHEN HE LOOKED UP AND SAW THE CABIN ALT OF 9000 FT AND CLBING. HE SAID THE CABIN IS CLBING THROUGH 9000 FT AND HE IMMEDIATELY RADIOED ATC FOR A LOWER ALT STATING THAT WE HAVE A PRESSURIZATION PROB. AFTER THAT THE CABIN ALT WARNING HORN SOUNDED; I SILENCED IT; AND THE CAPT STARTED THE INTERMITTENT WARNING HORN/INFLT CABIN ALT/RAPID DEPRESSURIZATION QRC OF WHICH WE PERFORMED OUR MEMORY ITEMS AND RAN THE REST OF THE QRC. DURING THIS ATC GAVE US FL250; AND WE DSNDED AT 3000 FPM IN THE HOPES THAT WE WOULD CATCH THE CABIN AND POSSIBLY REGAIN CTL. CTR THEN GAVE US FL210 AND FINALLY 16000 FT. ONCE WE WENT TO MANUAL AC (ACCORDING TO THE QRC) THE CABIN RATE INDICATOR IMMEDIATELY WENT TO A 2500 FPM DSCNT AND LEAVING FL210 WE NOTICED THE CABIN ALT NOW BELOW 10000 FT. AT THIS TIME WE INFORMED ATC THAT WE HAVE RECAPTURED OUR PRESSURIZATION AND THAT IT WAS HOLDING AND THAT WE WOULD LIKE TO LEVEL OFF AT FL190 AT WHICH WE DID DO. THEN WE TOOK OFF OUR MASKS. WE KNEW THAT THE RUBBER JUNGLE DEPLOYED AS THE CABIN ALT DID REACH 15000 FT. WE DO NOT RECALL SEEING AN AUTOFAIL LIGHT. ALSO THE STANDBY CTLR NEVER TOOK OVER AS THE FIRST GREEN LIGHT I SAW WAS THE MANUAL LIGHT. ONCE WE DID LEVEL OFF AT FL190; CTR ASKED US WHAT OUR INTENTIONS WERE. THE CAPT DISCUSSED WITH ME THAT OUR PRESSURIZATION IS UNDER CTL AND CONSIDERED TO PROCEED TO DEST. AT WHICH TIME; I PLUGGED IN OUR NEW CRUISE ALT OF FL190 INTO THE FMC AND REVIEWED THE PROGRESS PAGE TO SEE THE FUEL WE WOULD LAND AT (6.2) AND SAID THAT I WAS COMFORTABLE WITH THAT DECISION. AFTER WE HAVE STATED OUR INTENTIONS TO ATC; THE CAPT TALKED TO THE PURSER; DISPATCH AND MAINT. ONCE WE GOT HANDED OFF TO CTR WE WERE GIVEN A XING RESTR AT 11000 FT. WE PROCEEDED WITH THE CLRNC. I PROCEEDED TO GET THE ATIS AND LNDG DATA FOR OUR ARR AS THE CAPT WAS STILL WITH DISPATCH AND MAINT. WHEN HE CAME BACK; I INFORMED HIM OF OUR NEW ALT ASSIGNMENT AND OF CURRENT WX AND LNDG INFO. I ASKED HIM IF THE PURSER SAW ANY ABNORMALITIES; HE SAID NO; AND WE PROCEEDED TO RUN THE APCH/DSCNT CHKLIST AND SET UP FOR OUR ARR. UNFORTUNATELY; WE FORGOT THE DEFINITION OF 'MANUAL' AND NEGLECTED TO ADJUST THE OUTFLOW VALVE FOR THE DSCNT. THE CABIN STARTED TO BUMP AND WE NOTICED THAT THE CABIN ALT WAS BELOW 'SL.' I IMMEDIATELY ADJUSTED THE OUTFLOW VALVE (OVER CORRECTING) AT WHICH THE CABIN BEGAN TO CLB BTWN 1500-2500 FPM. I ASKED THE CAPT TO FINISH WITH THE IRREGULAR PROC FOR AUTOFAIL LIGHT/UNSCHEDULED PRESSURIZATION. ONCE HE STATED STANDBY MODE ON THE CTLR; THE CABIN REGAINED CTL AND WE PROCEEDED TO LAND WITHOUT FURTHER INCIDENT. ONCE AT THE GATE; THE CUST SVC REP CAME ON BOARD TO INFORM US THAT 2-3 PAX WERE COMPLAINING ABOUT DISCOMFORT IN THEIR EARS. HINDSIGHT; I THINK WE SHOULD HAVE LEVELED OFF AT A LOWER ALT ON OUR WAY TO OUR CRUISE ALT OF FL330 AND SPOKE TO MAINT EARLIER. SECONDLY; ACTUALLY TAKE OUT THE ACFT LOG HISTORY AND REVIEW IT (BECAUSE I THOUGHT THAT THE SPLIT DUCT WAS PREVIOUSLY RPTED) WHEN IN FACT IT WAS THE APU DUCT PUTTING OUT LOW PRESSURE WRITE-UP THAT I WAS REFING.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.