Narrative:

Preflight in ZZZ. WX very cold and clear. Outside air temperature 7 degrees F. During walkaround; I noted pressurization outflow valve closed per cold WX procedures. It was the first time I recall seeing that condition on my walkaround. Captain did cockpit preflight; setting pressurization selector to automatic after I returned from walkaround. Shortly before pushback a water line in aft galley split; gushing water in aft galley area. Maintenance secured leak and deferred the fix. Water to aft galley was shut off. Cleaners cleaned up water in aft galley area. Flight attendants indicated we had over 1 inch of water in the rear of the aircraft. We departed the gate 2 mins late. I was the PF. Climb was normal. At leveloff; FL350; captain noticed cabin rate of change fluxing +/-800-1000 ft; cabin altitude at 8000 ft. The cabin outflow valve was approximately at the first tic mark above full closed. All switches were checked and indications appeared normal. Captain directed me to switch cabin controller to alternate cabin; rate of change continued to flux and began to show a very slow climb. Next; he directed me to switch controller to manual; attempted to gain control of cabin altitude at 9000 ft outflow valve would not indicate full closed. Outflow valve would stop approximately at the same spot as in automatic and alternate mode. The cabin continued to a slow climb. I told the captain to get clearance to 10000 ft and I donned my oxygen mask. Let him work impending emergency. That pretty much covered the automatic fail/unscheduled pressurization checklist. Captain requested FL290; and I started down with the power up; hoping to keep cabin pressure below 10000 ft and wondering why we were descending to only FL290. Captain was still on radio discussing radar coverage and frequencys in case ATC contact was lost. At approximately FL300 cabin altitude warning horn went off. Captain donned his mask; extinguished the horn; got clearance to 10000 ft; a turn to ZZZ; and began working checklists while still coordinating frequencys and radar contact with ATC; as we were over the water and about to exit ATC coverage. Radios were never relinquished to me. During the turn I switched off the autoplt. Captain directed the autoplt be engaged and then he selected level change descent (power at idle) on the MCP; apparently; abandoning the power on descent. Shortly after level changed was engaged; the master caution light illuminated. I noted passenger oxygen light illuminated indicating we had failed to keep the cabin altitude below 14000 ft and the level change descent had apparently accelerated our depressurization with the power back. Passing through approximately FL180; I noted the speed brake was not deployed indicating we had never really accomplished the emergency descent checklist. Nor do I recall the completion of the cabin altitude warning horn or rapid depressurization checklist. Although the captain indicated he had accomplished the checklists. At 10000 ft; I noted the pressurization controller in automatic and outflow valve full open. I switched the controller to manual and closed outflow valve to maintain 7000 ft (approximately first tic). I did not attempt to see if outflow valve would fully close. Descending out of 10000 ft the captain positioned the controller back to automatic. The captain checked with the back to ensure everyone was ok and had everyone remove their masks at 10000 ft. The flight attendants indicated some of the masks did not work and I had a discussion about it with them. Landing was uneventful. Maintenance reported seeing some ice around the outflow valve at the gate and suggested that possibly water from the earlier leak had flowed back down and froze during climb out not allowing full closure of the outflow valve at altitude. Human performance considerations: PF should do ATC communication; freeing up PNF to focus on checklists. If autoplt is working fine; do not shut it off -- it frees one up enough to stay in the loop better. Altitude warning horn is too loud and distracting; they should be changed to a voice telling you to don oxygen mask (like many other warnings); it is impossible to communicate with it going off. In hindsight it appears full completion of the checklist may havetaken back seat to act/cabin communication; in a rapidly changing environment with communication hampered by the full face oxygen masks. Also the transition from a power on descent to an emergency descent was not real clear cut; although it should have been once the cabin reached 14000 ft. Had we focused more on the 3 emergency checklists; we would have ensured all items were completed. However; the ultimate outcome I do not believe would have been any different.

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Original NASA ASRS Text

Title: B737-800 FLT CREW EXPERIENCES PRESSURIZATION FAILURE LIKELY RELATED TO WATER SPILL IN AFT CABIN OVER PRESSURIZATION OUTFLOW VALVES DURING PREFLT IN VERY COLD CONDITIONS. CRM AND SOP ISSUES ARE MAGNIFIED DURING PERFORMANCE OF CHECKLISTS AND EMERGENCY DESCENT.

Narrative: PREFLT IN ZZZ. WX VERY COLD AND CLR. OUTSIDE AIR TEMP 7 DEGS F. DURING WALKAROUND; I NOTED PRESSURIZATION OUTFLOW VALVE CLOSED PER COLD WX PROCS. IT WAS THE FIRST TIME I RECALL SEEING THAT CONDITION ON MY WALKAROUND. CAPT DID COCKPIT PREFLT; SETTING PRESSURIZATION SELECTOR TO AUTO AFTER I RETURNED FROM WALKAROUND. SHORTLY BEFORE PUSHBACK A WATER LINE IN AFT GALLEY SPLIT; GUSHING WATER IN AFT GALLEY AREA. MAINT SECURED LEAK AND DEFERRED THE FIX. WATER TO AFT GALLEY WAS SHUT OFF. CLEANERS CLEANED UP WATER IN AFT GALLEY AREA. FLT ATTENDANTS INDICATED WE HAD OVER 1 INCH OF WATER IN THE REAR OF THE ACFT. WE DEPARTED THE GATE 2 MINS LATE. I WAS THE PF. CLB WAS NORMAL. AT LEVELOFF; FL350; CAPT NOTICED CABIN RATE OF CHANGE FLUXING +/-800-1000 FT; CABIN ALT AT 8000 FT. THE CABIN OUTFLOW VALVE WAS APPROX AT THE FIRST TIC MARK ABOVE FULL CLOSED. ALL SWITCHES WERE CHKED AND INDICATIONS APPEARED NORMAL. CAPT DIRECTED ME TO SWITCH CABIN CONTROLLER TO ALTERNATE CABIN; RATE OF CHANGE CONTINUED TO FLUX AND BEGAN TO SHOW A VERY SLOW CLB. NEXT; HE DIRECTED ME TO SWITCH CONTROLLER TO MANUAL; ATTEMPTED TO GAIN CTL OF CABIN ALT AT 9000 FT OUTFLOW VALVE WOULD NOT INDICATE FULL CLOSED. OUTFLOW VALVE WOULD STOP APPROX AT THE SAME SPOT AS IN AUTO AND ALTERNATE MODE. THE CABIN CONTINUED TO A SLOW CLB. I TOLD THE CAPT TO GET CLRNC TO 10000 FT AND I DONNED MY OXYGEN MASK. LET HIM WORK IMPENDING EMER. THAT PRETTY MUCH COVERED THE AUTO FAIL/UNSCHEDULED PRESSURIZATION CHKLIST. CAPT REQUESTED FL290; AND I STARTED DOWN WITH THE PWR UP; HOPING TO KEEP CABIN PRESSURE BELOW 10000 FT AND WONDERING WHY WE WERE DSNDING TO ONLY FL290. CAPT WAS STILL ON RADIO DISCUSSING RADAR COVERAGE AND FREQS IN CASE ATC CONTACT WAS LOST. AT APPROX FL300 CABIN ALT WARNING HORN WENT OFF. CAPT DONNED HIS MASK; EXTINGUISHED THE HORN; GOT CLRNC TO 10000 FT; A TURN TO ZZZ; AND BEGAN WORKING CHKLISTS WHILE STILL COORDINATING FREQS AND RADAR CONTACT WITH ATC; AS WE WERE OVER THE WATER AND ABOUT TO EXIT ATC COVERAGE. RADIOS WERE NEVER RELINQUISHED TO ME. DURING THE TURN I SWITCHED OFF THE AUTOPLT. CAPT DIRECTED THE AUTOPLT BE ENGAGED AND THEN HE SELECTED LEVEL CHANGE DSCNT (PWR AT IDLE) ON THE MCP; APPARENTLY; ABANDONING THE PWR ON DSCNT. SHORTLY AFTER LEVEL CHANGED WAS ENGAGED; THE MASTER CAUTION LIGHT ILLUMINATED. I NOTED PAX OXYGEN LIGHT ILLUMINATED INDICATING WE HAD FAILED TO KEEP THE CABIN ALT BELOW 14000 FT AND THE LEVEL CHANGE DSCNT HAD APPARENTLY ACCELERATED OUR DEPRESSURIZATION WITH THE PWR BACK. PASSING THROUGH APPROX FL180; I NOTED THE SPD BRAKE WAS NOT DEPLOYED INDICATING WE HAD NEVER REALLY ACCOMPLISHED THE EMER DSCNT CHKLIST. NOR DO I RECALL THE COMPLETION OF THE CABIN ALT WARNING HORN OR RAPID DEPRESSURIZATION CHKLIST. ALTHOUGH THE CAPT INDICATED HE HAD ACCOMPLISHED THE CHKLISTS. AT 10000 FT; I NOTED THE PRESSURIZATION CONTROLLER IN AUTO AND OUTFLOW VALVE FULL OPEN. I SWITCHED THE CONTROLLER TO MANUAL AND CLOSED OUTFLOW VALVE TO MAINTAIN 7000 FT (APPROX FIRST TIC). I DID NOT ATTEMPT TO SEE IF OUTFLOW VALVE WOULD FULLY CLOSE. DSNDING OUT OF 10000 FT THE CAPT POSITIONED THE CONTROLLER BACK TO AUTO. THE CAPT CHKED WITH THE BACK TO ENSURE EVERYONE WAS OK AND HAD EVERYONE REMOVE THEIR MASKS AT 10000 FT. THE FLT ATTENDANTS INDICATED SOME OF THE MASKS DID NOT WORK AND I HAD A DISCUSSION ABOUT IT WITH THEM. LNDG WAS UNEVENTFUL. MAINT RPTED SEEING SOME ICE AROUND THE OUTFLOW VALVE AT THE GATE AND SUGGESTED THAT POSSIBLY WATER FROM THE EARLIER LEAK HAD FLOWED BACK DOWN AND FROZE DURING CLBOUT NOT ALLOWING FULL CLOSURE OF THE OUTFLOW VALVE AT ALT. HUMAN PERFORMANCE CONSIDERATIONS: PF SHOULD DO ATC COM; FREEING UP PNF TO FOCUS ON CHKLISTS. IF AUTOPLT IS WORKING FINE; DO NOT SHUT IT OFF -- IT FREES ONE UP ENOUGH TO STAY IN THE LOOP BETTER. ALT WARNING HORN IS TOO LOUD AND DISTRACTING; THEY SHOULD BE CHANGED TO A VOICE TELLING YOU TO DON OXYGEN MASK (LIKE MANY OTHER WARNINGS); IT IS IMPOSSIBLE TO COMMUNICATE WITH IT GOING OFF. IN HINDSIGHT IT APPEARS FULL COMPLETION OF THE CHKLIST MAY HAVETAKEN BACK SEAT TO ACT/CABIN COM; IN A RAPIDLY CHANGING ENVIRONMENT WITH COM HAMPERED BY THE FULL FACE OXYGEN MASKS. ALSO THE TRANSITION FROM A PWR ON DSCNT TO AN EMER DSCNT WAS NOT REAL CLR CUT; ALTHOUGH IT SHOULD HAVE BEEN ONCE THE CABIN REACHED 14000 FT. HAD WE FOCUSED MORE ON THE 3 EMER CHKLISTS; WE WOULD HAVE ENSURED ALL ITEMS WERE COMPLETED. HOWEVER; THE ULTIMATE OUTCOME I DO NOT BELIEVE WOULD HAVE BEEN ANY DIFFERENT.

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.