Narrative:

At the top of descent from FL290; we experienced a rapid depressurization. The intermittent warning horn sounded. We donned our O2 masks. We recognized the cabin altitude was passing 10;000 ft and climbing at about 3;000 FPM. I directed the first officer to run the cabin altitude warning/abnormal pressurization QRH checklist. While the first officer started that; I began an emergency descent to 10;000 ft at about 3;500-4;000 FPM and coordinated with ATC. The pressurization outflow valve was already in the full closed position; but when the first officer switched the pressurization controller to manual mode and toggled the outflow valve switch to full closed; the cabin began to descend at about 3;000 FPM. During the descent it was difficult to control the pressurization. At one point the cabin descended below sea-level. The first officer finally got it stabilized at about 1;000 ft and left it there. The cabin never climbed past about 12;000 ft throughout the process so the masks in the cabin never dropped. We informed the flight attendants about the problem; but not the passengers. We landed without further incident and taxied to the gate.in some respects I am suspicious that the emergency descent made the situation worse. If we had pushed the power back up and coordinated for a more gradual descent (1;000 FPM or so) I believe the cabin might have maintained pressurization. In other words; I think the pressurization loss occurred because of a leaky airplane and a lack of incoming air from the bleed air system when the engines were reduced to idle for the descent. I do not know this for sure; but in retrospect I think this might have been the case.

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Original NASA ASRS Text

Title: B737 Captain experiences loss of cabin pressurization at the start of descent. An emergency descent is initiated while the First Officer is able to regain control of pressurization using manual control of the outflow valve.

Narrative: At the top of descent from FL290; we experienced a rapid depressurization. The intermittent warning horn sounded. We donned our O2 masks. We recognized the cabin altitude was passing 10;000 FT and climbing at about 3;000 FPM. I directed the First Officer to run the Cabin Altitude Warning/Abnormal Pressurization QRH Checklist. While the First Officer started that; I began an emergency descent to 10;000 FT at about 3;500-4;000 FPM and coordinated with ATC. The pressurization outflow valve was already in the full closed position; but when the First Officer switched the pressurization controller to manual mode and toggled the outflow valve switch to full closed; the cabin began to descend at about 3;000 FPM. During the descent it was difficult to control the pressurization. At one point the cabin descended below sea-level. The First Officer finally got it stabilized at about 1;000 FT and left it there. The cabin never climbed past about 12;000 FT throughout the process so the masks in the cabin never dropped. We informed the Flight Attendants about the problem; but not the passengers. We landed without further incident and taxied to the gate.In some respects I am suspicious that the emergency descent made the situation worse. If we had pushed the power back up and coordinated for a more gradual descent (1;000 FPM or so) I believe the cabin might have maintained pressurization. In other words; I think the pressurization loss occurred because of a leaky airplane and a lack of incoming air from the bleed air system when the engines were reduced to idle for the descent. I do not know this for sure; but in retrospect I think this might have been the case.

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.