Narrative:

Warning horn began sounding. I immediately stated aloud the first two steps of the cabin altitude warning/abnormal pressurization checklist; donned my O2 mask and turned on my overhead speaker. I verified that that both bleeds and both packs were on and confirmed that the cabin altitude was in fact approaching 10;000 ft. The first officer requested an emergency descent from center and after I began to descend I made a PA notifying the passengers that we were having problems with our pressurization system and were making a precautionary descent to 10;000 ft. The first officer took out the QRH and began to run through the abnormal pressurization checklist and when he selected manual on the pressurization controller the cabin immediately began climbing at approximately 3;000 FPM. I directed the first officer to return the controller to auto and the cabin rate returned to near 0 FPM. After reaching 10;000 ft we unmasked and I made another PA to the passengers telling them that we had reached an altitude where supplemental O2 was no longer required and that all aircraft systems were now operating normally. I called the flight attendants to check on their status and the status of the passengers and was told that 'everyone's fine'. I next went to the fix page and checked the distance to at approximately xa:45 while cruising at FL370 en route from departure city to our destination the cabin altitude; departure (220 NM) and destination (290 NM) and told the first officer that my intentions were to continue to scheduled destination airport. He notified ATC and we were given direct routing that airport. At this time I received a message from dispatch stating that they had noticed my descent and were waiting on VHF for a call. I contacted dispatch and told them that all systems now appeared to be operating normally; that the passengers and crew were okay and that my intention was to continue on to destination at 10;000 ft. The dispatcher queried my arrival fuel and after I told him 5.7K he said that wasn't the number he was coming up with which keyed me into the fact that I had not reset my cruise altitude to 10;000 ft. After making the change to the FMC I determined that our arrival fuel would be 4.8K and stated that I was still planning on continuing. We agreed on this course of action and I then passed along to the passengers that we were continuing on to our originally scheduled destination; that customer service personnel would be meeting our plane and that I would also be available to answer any questions during deplaning. Our flight landed uneventfully with 4.7K and we blocked in with 4.4K three minutes ahead of schedule at xb:42. During deplaning two or three people stopped to thank me for keeping them informed during the flight and none of the eighteen passengers took the opportunity to talk with the costumer services. Maintenance met the aircraft while I called dispatch; my chief pilot; scheduler and maintenance control. I also contacted center to confirm that we had not declared an emergency and was told that they had not noted any emergency. Our next leg was canceled; the pressurization system was MEL'ed and we conducted an unpressurized ferry flight to a maintenance facility where we resumed our sequence. I have several lessons learned from this event: 1) pilots need additional training on the location the cabin altitude warning horn cutout button. I've had this warning sound twice in flight as a captain and neither time did the first officer realize that there was a cutout until I located it and silenced the horn. It wasn't easy for me to find as the button isn't on the pressurization panel and is never used or tested during preflight. Having the horn blaring during the first 30 seconds of a pressurization emergency is quite distracting and adds to the tension in the cockpit as well as disrupting both internal and external communication. 2) pilots need to practice running an emergency checklist; making PA's; andcalling ATC all while wearing an O2 mask and using the overhead speaker for communication. It is much more difficult to do than you would think and would be an excellent scenario for a pt or loft.3) the MEL for operating unpressurized with one or two packs operating is extremely confusing and difficult to understand. It took a conference call between the chief pilot on duty; dispatch; and maintenance control to clarify exactly how to conduct the ferry flight.

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Original NASA ASRS Text

Title: A B737-300's Cabin Altitude Warn Horn sounded in cruise at FL370. An emergency descent was begun to 10;000 FT; the QRH procedure completed and the flight continued to its destination. The First Officer could not locate the warning horn cutout button.

Narrative: Warning Horn began sounding. I immediately stated aloud the first two steps of the Cabin Altitude Warning/Abnormal Pressurization checklist; donned my O2 mask and turned on my overhead speaker. I verified that that both bleeds and both packs were on and confirmed that the cabin altitude was in fact approaching 10;000 FT. The First Officer requested an emergency descent from Center and after I began to descend I made a PA notifying the passengers that we were having problems with our pressurization system and were making a precautionary descent to 10;000 ft. The First Officer took out the QRH and began to run through the Abnormal Pressurization checklist and when he selected manual on the pressurization controller the cabin immediately began climbing at approximately 3;000 FPM. I directed the First Officer to return the controller to auto and the cabin rate returned to near 0 FPM. After reaching 10;000 FT we unmasked and I made another PA to the passengers telling them that we had reached an altitude where supplemental O2 was no longer required and that all aircraft systems were now operating normally. I called the Flight Attendants to check on their status and the status of the passengers and was told that 'everyone's fine'. I next went to the fix page and checked the distance to At approximately XA:45 while cruising at FL370 en route from departure city to our destination the Cabin Altitude; departure (220 NM) and destination (290 NM) and told the First Officer that my intentions were to continue to scheduled destination airport. He notified ATC and we were given direct routing that airport. At this time I received a message from Dispatch stating that they had noticed my descent and were waiting on VHF for a call. I contacted Dispatch and told them that all systems now appeared to be operating normally; that the passengers and crew were OKAY and that my intention was to continue on to destination at 10;000 FT. The Dispatcher queried my arrival fuel and after I told him 5.7K he said that wasn't the number he was coming up with which keyed me into the fact that I had not reset my cruise altitude to 10;000 FT. After making the change to the FMC I determined that our arrival fuel would be 4.8K and stated that I was still planning on continuing. We agreed on this course of action and I then passed along to the passengers that we were continuing on to our originally scheduled destination; that customer service personnel would be meeting our plane and that I would also be available to answer any questions during deplaning. Our flight landed uneventfully with 4.7K and we blocked in with 4.4K three minutes ahead of schedule at XB:42. During deplaning two or three people stopped to thank me for keeping them informed during the flight and none of the eighteen passengers took the opportunity to talk with the costumer services. Maintenance met the aircraft while I called Dispatch; my Chief Pilot; scheduler and maintenance control. I also contacted Center to confirm that we had not declared an emergency and was told that they had not noted any emergency. Our next leg was canceled; the pressurization system was MEL'ed and we conducted an unpressurized ferry flight to a Maintenance Facility where we resumed our sequence. I have several lessons learned from this event: 1) Pilots need additional training on the location the cabin altitude warning horn cutout button. I've had this warning sound twice in flight as a Captain and neither time did the First Officer realize that there was a cutout until I located it and silenced the horn. It wasn't easy for me to find as the button isn't on the pressurization panel and is never used or tested during preflight. Having the horn blaring during the first 30 seconds of a pressurization emergency is quite distracting and adds to the tension in the cockpit as well as disrupting both internal and external communication. 2) Pilots need to practice running an emergency checklist; making PA's; andcalling ATC all while wearing an O2 mask and using the overhead speaker for communication. It is much more difficult to do than you would think and would be an excellent scenario for a PT or LOFT.3) The MEL for operating unpressurized with one or two packs operating is extremely confusing and difficult to understand. It took a conference call between the Chief Pilot on Duty; Dispatch; and Maintenance Control to clarify exactly how to conduct the ferry flight.

Data retrieved from NASA's ASRS site as of April 2012 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.