Narrative:

Cruising at FL370 (first officer flying). We were given a descent to 12000 ft and began about 1500 FPM. I went off to get ATIS and passing FL330, we got a master caution light with no overhead lights. Approximately 5-10 seconds alter, the automatic fail light illuminated on the pressurization (digital) control panel. Both altitude setting windows on the panel displayed dashes. I called for the automatic fail light/unscheduled pressurization checklist. I started flying the plane and the first officer ran the checklist. When we selected altitude check, there were no green lights on the panel and the altitude setting windows were still dashes. The pressurization was beginning to oscillate uncomfortably with a lot of pressure and very little pressure. The flight attendants called, reported the discomfort. I acknowledged and told them we were working on it. We selected manual, the outflow valve needle was full closed, and we could not make it move either way. We continued to descend and the aircraft began to over pressure and became increasingly uncomfortable. I shallowed the descent to try to help the pressure stabilize. At times, this appeared it might work, but ultimately did not. I made a PA to the passenger to tell them we were aware of the pressure and we were working on it. The pressure rate, differential, and cabin altitude needles made numerous swings. Passing through approximately FL250 the differential pressure needle quickly exceeded the red arc and the cabin pressurization was down around 2000 ft or less. At that time, the cabin pressure failed, the altitude warning horn sounded and we experienced a rapid loss of pressure, and the passenger oxygen masks deployed. We initiated an emergency descent, called for the rapid depressurization checklist. The 'a' flight attendant called and said the masks were deployed. I told them we had lost pressurization and to put the masks on. The first officer declared an emergency, I made a PA to the passenger to follow the flight attendant instructions and tried to calm them as to what was going on. The cabin did have vapor and condensation on the windows. We were cleared to 7000 ft by ATC and continued down. The outflow valve was totally unresponsive during the descent. At 7000 ft the pressurization controller attempted to pressurize again (over pressurize). The first officer cycled the switch between normal/altitude/manual and the outflow valve started to open. We were able to keep it open. I gave the plane to the first officer and I called company and dispatch. We continued to sjc, descended to pattern altitude for a visual approach to runway 12R. I made a PA to the passenger that they could remove their masks and updated them on what we were doing. I explained to them that they would see fire trucks and flashing lights and not to be alarmed by them, that they would follow us to the gate. I had the flight attendant secure the cabin and we performed the approach/descent checklist. The first officer flew the visual approach and landing to runway 12R. Taxi to the gate was uneventful. Most passenger seemed somewhat shaken and 2 passenger were treated by fire personnel. Customer service helped very much. My crew was exceptional. They acted promptly, professionally, and were a great asset during a very uncomfortable time. Most passenger continued with us to ont on another plane. I heard 4 or 5 chose not to go. Again, I want to say that first officer did an exceptional job and was calm and professional during this whole situation. He was a great help. Thoughts: the frustrating thing about this was the fact that I was really not sure of a procedure for over pressurization at altitude. I could have turned the bleeds off, but I would have created a depressurization at altitude. Ultimately, this occurred anyway, but I was unsure of an actual procedure. Also, the flight attendants should be taught that when the masks fall and a depressurization occurs, they should hang on for a rapid descent. I started ours very gradually, but it would be easy to throw them around. Also, some of the passenger pulled their oxygen masks out of the ceiling. This creates some confusion for the flight attendants. Supplemental information from acn 573580: approximately 80 mi from sjc, we received a descent clearance to 12000 ft. Descending THROUGHFL330, the master caution came on. The captain and I looked for the associated light and could not find one. About 10 seconds later, the automatic fail light came on on the pressurization panel. Captain called for the automatic fail checklist, and he started reading it. We switched to 'altn,' but the green light did not come on. I also noticed the cabin altitude and airport elevation windows went to all dashes. At this point, I gave control of the aircraft to the captain so I could run the checklist and work on the panel. At this time, the pressure began to oscillate and our ears began to pop. Then it seemed to stabilize again. Going to manual did not help either. The valve was all the way closed and would not move. The whole pressure controller failed. The oscillations began again and got worse. The differential pressure climbed above 9.0 quickly. The aircraft went into rapid depressurization mode at FL250. We performed our memory items and established communication. The captain talked to the flight attendant and passenger while I declared the emergency to ATC. ATC then cleared us to 7000 ft. I looked up at the manual mode and the valve was still stuck on the closed position. At 7000 ft, we took off our masks. I reached up and cycled the switch through automatic, 'altn', and manual modes a couple of times. The 'altn' green light then came on and the digits came back on in the windows. The aircraft did try to re-pressurize again, but we were able to control it in manual mode. I resumed control of the aircraft and the captain performed the approach descent checklist, called sjc and dispatch and secured the cabin. The rest of the flight was normal. There is no QRH checklist for loss of the whole pressure controller. The checklist we followed assumed we were losing pressure. While the pressure was oscillating, I wasn't sure if the pressure was increasing or decreasing -- finally it decided to over pressurize and the emergency valve opened at FL250. At that point, our training tool over and everything went as expected. I think if this is a common problem we need to know about and be trained as to what to do if we become over pressurized at altitude. If we turn off the bleeds, will that also initiate a rapid depressurization? What would happen if we just turned off 1 bleed? Unfortunately, things were happening so fast and the oscillations were confusing, so we did not try those things.

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Original NASA ASRS Text

Title: A B737-300 CREW LOST CTL OF CABIN PRESSURIZATION, AND THEN HAD A CABIN OVER PRESSURIZATION.

Narrative: CRUISING AT FL370 (FO FLYING). WE WERE GIVEN A DSCNT TO 12000 FT AND BEGAN ABOUT 1500 FPM. I WENT OFF TO GET ATIS AND PASSING FL330, WE GOT A MASTER CAUTION LIGHT WITH NO OVERHEAD LIGHTS. APPROX 5-10 SECONDS ALTER, THE AUTO FAIL LIGHT ILLUMINATED ON THE PRESSURIZATION (DIGITAL) CTL PANEL. BOTH ALT SETTING WINDOWS ON THE PANEL DISPLAYED DASHES. I CALLED FOR THE AUTO FAIL LIGHT/UNSCHEDULED PRESSURIZATION CHKLIST. I STARTED FLYING THE PLANE AND THE FO RAN THE CHKLIST. WHEN WE SELECTED ALT CHK, THERE WERE NO GREEN LIGHTS ON THE PANEL AND THE ALT SETTING WINDOWS WERE STILL DASHES. THE PRESSURIZATION WAS BEGINNING TO OSCILLATE UNCOMFORTABLY WITH A LOT OF PRESSURE AND VERY LITTLE PRESSURE. THE FLT ATTENDANTS CALLED, RPTED THE DISCOMFORT. I ACKNOWLEDGED AND TOLD THEM WE WERE WORKING ON IT. WE SELECTED MANUAL, THE OUTFLOW VALVE NEEDLE WAS FULL CLOSED, AND WE COULD NOT MAKE IT MOVE EITHER WAY. WE CONTINUED TO DSND AND THE ACFT BEGAN TO OVER PRESSURE AND BECAME INCREASINGLY UNCOMFORTABLE. I SHALLOWED THE DSCNT TO TRY TO HELP THE PRESSURE STABILIZE. AT TIMES, THIS APPEARED IT MIGHT WORK, BUT ULTIMATELY DID NOT. I MADE A PA TO THE PAX TO TELL THEM WE WERE AWARE OF THE PRESSURE AND WE WERE WORKING ON IT. THE PRESSURE RATE, DIFFERENTIAL, AND CABIN ALT NEEDLES MADE NUMEROUS SWINGS. PASSING THROUGH APPROX FL250 THE DIFFERENTIAL PRESSURE NEEDLE QUICKLY EXCEEDED THE RED ARC AND THE CABIN PRESSURIZATION WAS DOWN AROUND 2000 FT OR LESS. AT THAT TIME, THE CABIN PRESSURE FAILED, THE ALT WARNING HORN SOUNDED AND WE EXPERIENCED A RAPID LOSS OF PRESSURE, AND THE PAX OXYGEN MASKS DEPLOYED. WE INITIATED AN EMER DSCNT, CALLED FOR THE RAPID DEPRESSURIZATION CHKLIST. THE 'A' FLT ATTENDANT CALLED AND SAID THE MASKS WERE DEPLOYED. I TOLD THEM WE HAD LOST PRESSURIZATION AND TO PUT THE MASKS ON. THE FO DECLARED AN EMER, I MADE A PA TO THE PAX TO FOLLOW THE FLT ATTENDANT INSTRUCTIONS AND TRIED TO CALM THEM AS TO WHAT WAS GOING ON. THE CABIN DID HAVE VAPOR AND CONDENSATION ON THE WINDOWS. WE WERE CLRED TO 7000 FT BY ATC AND CONTINUED DOWN. THE OUTFLOW VALVE WAS TOTALLY UNRESPONSIVE DURING THE DSCNT. AT 7000 FT THE PRESSURIZATION CTLR ATTEMPTED TO PRESSURIZE AGAIN (OVER PRESSURIZE). THE FO CYCLED THE SWITCH BTWN NORMAL/ALT/MANUAL AND THE OUTFLOW VALVE STARTED TO OPEN. WE WERE ABLE TO KEEP IT OPEN. I GAVE THE PLANE TO THE FO AND I CALLED COMPANY AND DISPATCH. WE CONTINUED TO SJC, DSNDED TO PATTERN ALT FOR A VISUAL APCH TO RWY 12R. I MADE A PA TO THE PAX THAT THEY COULD REMOVE THEIR MASKS AND UPDATED THEM ON WHAT WE WERE DOING. I EXPLAINED TO THEM THAT THEY WOULD SEE FIRE TRUCKS AND FLASHING LIGHTS AND NOT TO BE ALARMED BY THEM, THAT THEY WOULD FOLLOW US TO THE GATE. I HAD THE FLT ATTENDANT SECURE THE CABIN AND WE PERFORMED THE APCH/DSCNT CHKLIST. THE FO FLEW THE VISUAL APCH AND LNDG TO RWY 12R. TAXI TO THE GATE WAS UNEVENTFUL. MOST PAX SEEMED SOMEWHAT SHAKEN AND 2 PAX WERE TREATED BY FIRE PERSONNEL. CUSTOMER SVC HELPED VERY MUCH. MY CREW WAS EXCEPTIONAL. THEY ACTED PROMPTLY, PROFESSIONALLY, AND WERE A GREAT ASSET DURING A VERY UNCOMFORTABLE TIME. MOST PAX CONTINUED WITH US TO ONT ON ANOTHER PLANE. I HEARD 4 OR 5 CHOSE NOT TO GO. AGAIN, I WANT TO SAY THAT FO DID AN EXCEPTIONAL JOB AND WAS CALM AND PROFESSIONAL DURING THIS WHOLE SIT. HE WAS A GREAT HELP. THOUGHTS: THE FRUSTRATING THING ABOUT THIS WAS THE FACT THAT I WAS REALLY NOT SURE OF A PROC FOR OVER PRESSURIZATION AT ALT. I COULD HAVE TURNED THE BLEEDS OFF, BUT I WOULD HAVE CREATED A DEPRESSURIZATION AT ALT. ULTIMATELY, THIS OCCURRED ANYWAY, BUT I WAS UNSURE OF AN ACTUAL PROC. ALSO, THE FLT ATTENDANTS SHOULD BE TAUGHT THAT WHEN THE MASKS FALL AND A DEPRESSURIZATION OCCURS, THEY SHOULD HANG ON FOR A RAPID DSCNT. I STARTED OURS VERY GRADUALLY, BUT IT WOULD BE EASY TO THROW THEM AROUND. ALSO, SOME OF THE PAX PULLED THEIR OXYGEN MASKS OUT OF THE CEILING. THIS CREATES SOME CONFUSION FOR THE FLT ATTENDANTS. SUPPLEMENTAL INFO FROM ACN 573580: APPROX 80 MI FROM SJC, WE RECEIVED A DSCNT CLRNC TO 12000 FT. DSNDING THROUGHFL330, THE MASTER CAUTION CAME ON. THE CAPT AND I LOOKED FOR THE ASSOCIATED LIGHT AND COULD NOT FIND ONE. ABOUT 10 SECONDS LATER, THE AUTO FAIL LIGHT CAME ON ON THE PRESSURIZATION PANEL. CAPT CALLED FOR THE AUTO FAIL CHKLIST, AND HE STARTED READING IT. WE SWITCHED TO 'ALTN,' BUT THE GREEN LIGHT DID NOT COME ON. I ALSO NOTICED THE CABIN ALT AND ARPT ELEVATION WINDOWS WENT TO ALL DASHES. AT THIS POINT, I GAVE CTL OF THE ACFT TO THE CAPT SO I COULD RUN THE CHKLIST AND WORK ON THE PANEL. AT THIS TIME, THE PRESSURE BEGAN TO OSCILLATE AND OUR EARS BEGAN TO POP. THEN IT SEEMED TO STABILIZE AGAIN. GOING TO MANUAL DID NOT HELP EITHER. THE VALVE WAS ALL THE WAY CLOSED AND WOULD NOT MOVE. THE WHOLE PRESSURE CONTROLLER FAILED. THE OSCILLATIONS BEGAN AGAIN AND GOT WORSE. THE DIFFERENTIAL PRESSURE CLBED ABOVE 9.0 QUICKLY. THE ACFT WENT INTO RAPID DEPRESSURIZATION MODE AT FL250. WE PERFORMED OUR MEMORY ITEMS AND ESTABLISHED COM. THE CAPT TALKED TO THE FLT ATTENDANT AND PAX WHILE I DECLARED THE EMER TO ATC. ATC THEN CLRED US TO 7000 FT. I LOOKED UP AT THE MANUAL MODE AND THE VALVE WAS STILL STUCK ON THE CLOSED POS. AT 7000 FT, WE TOOK OFF OUR MASKS. I REACHED UP AND CYCLED THE SWITCH THROUGH AUTO, 'ALTN', AND MANUAL MODES A COUPLE OF TIMES. THE 'ALTN' GREEN LIGHT THEN CAME ON AND THE DIGITS CAME BACK ON IN THE WINDOWS. THE ACFT DID TRY TO RE-PRESSURIZE AGAIN, BUT WE WERE ABLE TO CTL IT IN MANUAL MODE. I RESUMED CTL OF THE ACFT AND THE CAPT PERFORMED THE APCH DSCNT CHKLIST, CALLED SJC AND DISPATCH AND SECURED THE CABIN. THE REST OF THE FLT WAS NORMAL. THERE IS NO QRH CHKLIST FOR LOSS OF THE WHOLE PRESSURE CONTROLLER. THE CHKLIST WE FOLLOWED ASSUMED WE WERE LOSING PRESSURE. WHILE THE PRESSURE WAS OSCILLATING, I WASN'T SURE IF THE PRESSURE WAS INCREASING OR DECREASING -- FINALLY IT DECIDED TO OVER PRESSURIZE AND THE EMER VALVE OPENED AT FL250. AT THAT POINT, OUR TRAINING TOOL OVER AND EVERYTHING WENT AS EXPECTED. I THINK IF THIS IS A COMMON PROB WE NEED TO KNOW ABOUT AND BE TRAINED AS TO WHAT TO DO IF WE BECOME OVER PRESSURIZED AT ALT. IF WE TURN OFF THE BLEEDS, WILL THAT ALSO INITIATE A RAPID DEPRESSURIZATION? WHAT WOULD HAPPEN IF WE JUST TURNED OFF 1 BLEED? UNFORTUNATELY, THINGS WERE HAPPENING SO FAST AND THE OSCILLATIONS WERE CONFUSING, SO WE DID NOT TRY THOSE THINGS.

Data retrieved from NASA's ASRS site as of July 2007 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.