Narrative:

ATC cleared pilot discretion to FL240. Shortly after acknowledging clearance cabin altitude warning horn sounded. Glanced at cabin altimeter; which indicated 10000 ft and immediately both pilots directed each other to don masks and execute memory items. Donned masks and established communications with each other. I called ATC and told them we had a cabin pressure issue and were initiating a descent to FL240 immediately and required lower. Captain initiated QRH for cabin altitude warning horn while I communicated with ATC. Cabin altitude continued to increase initially slowly; but started to increase rapidly after several seconds. Communicated to ATC emergency aircraft and needed lower immediately with clearance to 10000 ft MSL. ATC indicated traffic conflicts (traffic funneling due to thunderstorms) cleared to 16000 ft MSL and would have 10000 ft MSL shortly. ATC was dealing with another aircraft with pressurization issues in the same area. Cabin altitude continued to rise and captain called for emergency descent checklist. I read and verbalized the QRH and we executed the emergency descent checklist. While descending through approximately FL200 ATC cleared us to 10000 ft MSL. Approximately FL180-190 the cabin altitude increased to approximately 15000 ft and the pass oxy on light illuminated. Previously the captain had warned the flight attendants that the pass cabin masks might fall. During the descent and prior to the cabin altitude passing 14000 ft; I attempted several times to manually close the outflow valve with the control switch. The valve position indicator was indicating full closed and no movement on the gauge. After leveling at 10000 ft and approximately 80 miles from the original destination we proceeded direct. Removed oxygen masks and established normal communications in the cockpit. I told the captain I was reviewing the checklist to ensure all clean up items and notes were checked. During re-examination of the checklist I discovered the pressurization mode selector in manual AC/man -- the checklist called for dc/man. When the captain had initially started the checklist he moved the packs to high per the note in the checklist and attempted to put the mode selector in man dc and then close the outflow valve manually. The outflow valve indicator indicated full closed. I pointed out what the checklist indicated and subsequently moved it to dc man. In that position manually moving the control switch the valve indicator moved normally.

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Original NASA ASRS Text

Title: B737-500 experienced loss of pressurization control and declared an emergency. The crews' faulty use of the checklist contributed to the inability to restore pressurization.

Narrative: ATC cleared Pilot Discretion to FL240. Shortly after acknowledging clearance cabin altitude warning horn sounded. Glanced at cabin altimeter; which indicated 10000 FT and immediately both pilots directed each other to don masks and execute memory items. Donned masks and established communications with each other. I called ATC and told them we had a cabin pressure issue and were initiating a descent to FL240 immediately and required lower. Captain initiated QRH for cabin altitude warning horn while I communicated with ATC. Cabin altitude continued to increase initially slowly; but started to increase rapidly after several seconds. Communicated to ATC emergency aircraft and needed lower immediately with clearance to 10000 FT MSL. ATC indicated traffic conflicts (traffic funneling due to thunderstorms) cleared to 16000 FT MSL and would have 10000 FT MSL shortly. ATC was dealing with another aircraft with pressurization issues in the same area. Cabin altitude continued to rise and Captain called for Emergency Descent checklist. I read and verbalized the QRH and we executed the Emergency Descent checklist. While descending through approximately FL200 ATC cleared us to 10000 FT MSL. Approximately FL180-190 the cabin altitude increased to approximately 15000 FT and the PASS OXY on light illuminated. Previously the Captain had warned the flight attendants that the Pass Cabin Masks might fall. During the descent and prior to the cabin altitude passing 14000 FT; I attempted several times to manually close the outflow valve with the control switch. The valve position indicator was indicating full closed and no movement on the gauge. After leveling at 10000 FT and approximately 80 miles from the original destination we proceeded direct. Removed oxygen masks and established normal communications in the cockpit. I told the Captain I was reviewing the checklist to ensure all clean up items and notes were checked. During re-examination of the checklist I discovered the pressurization mode selector in manual AC/Man -- the checklist called for DC/Man. When the Captain had initially started the checklist he moved the PACKs to high per the note in the checklist and attempted to put the mode selector in Man DC and then close the outflow valve manually. The outflow valve indicator indicated full closed. I pointed out what the checklist indicated and subsequently moved it to DC Man. In that position manually moving the control switch the valve indicator moved normally.

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.