At FL270 a B737 cabin altitude warning horn sounded so an emergency was declared and the flight desc...

Narrative:

Previous flight en route had equipment cooling fan lights with both fans inoperative. Contract maintenance performed corrective action and completed logbook entry. On subsequent flight same problem occurred after passing approximately 10;000 ft MSL. [We were] cleared to FL340. Passing FL270 cabin altitude warning horn sounded. The pilot flying (captain) pointed to cabin altitude indicator at approximately 9;500 ft. Pilot flying immediately initiated descent. Pilot flying and pilot not flying donned O2 masks and established communications. Pilot not flying broadcasted to ATC that we had experienced a loss of pressurization; declared an emergency; and stated we were executing an emergency descent to 10;000 ft MSL. Pilot not flying opened checklist and commenced cabin altitude warning horn/abnormal pressurization checklist and emergency descent checklist while communicating with ATC. Packs were noted in high. (Pilot not flying had selected high after flap retraction for cooling.) engine bleeds were on and APU bleed off. There was no indication of a failed pressurization controller. 'Man dc' was selected and the outflow valve was closed manually. Cabin altitude began to descend. [We] leveled at 8;000 ft MSL (per ATC instructions). Pilot flying spoke with cabin crew and made a PA to the passengers as the pilot not flying coordinated approach and landing preparation with ATC. Pilot not flying programmed the FMC and got performance data for landing at the divert airport. Pilot not flying contacted operations and coordinated gate arrival. Pilot flying and pilot not flying discussed overweight landing considerations. [We] received vectors to visual final to runway 1. Landing was uneventful. After landing we both heard a loud tone and were unable to determine the source. We later discovered it was the lavatory fire/smoke warning. Completed checklist and pulled circuit breaker. No fires noted. Upon arrival at the gate; pilot flying observed the cabin was still pressurized. [Pilot flying] directed pilot not flying to slowly open outflow valve to depressurize the cabin. Pilot not flying (me) had failed to open the outflow valve after the aircraft was below 1;000 ft MSL.

Original NASA ASRS Text

Title: At FL270 a B737 Cabin Altitude Warning horn sounded so an emergency was declared and the flight descended to 8;000 FT. On this flight and the previous flight the Equip Cooling OFF light illuminated indicating a lack of air flow.

Narrative: Previous flight en route had equipment cooling fan lights with both fans inoperative. Contract Maintenance performed corrective action and completed logbook entry. On subsequent flight same problem occurred after passing approximately 10;000 FT MSL. [We were] cleared to FL340. Passing FL270 Cabin Altitude Warning horn sounded. The pilot flying (Captain) pointed to Cabin Altitude indicator at approximately 9;500 FT. Pilot flying immediately initiated descent. Pilot flying and pilot not flying donned O2 masks and established communications. Pilot not flying broadcasted to ATC that we had experienced a loss of pressurization; declared an emergency; and stated we were executing an emergency descent to 10;000 FT MSL. Pilot not flying opened checklist and commenced Cabin Altitude Warning Horn/Abnormal Pressurization Checklist and Emergency Descent Checklist while communicating with ATC. Packs were noted in high. (Pilot not flying had selected high after flap retraction for cooling.) Engine bleeds were ON and APU bleed OFF. There was no indication of a failed pressurization controller. 'Man DC' was selected and the outflow valve was closed manually. Cabin altitude began to descend. [We] leveled at 8;000 FT MSL (per ATC Instructions). Pilot flying spoke with cabin crew and made a PA to the passengers as the pilot not flying coordinated approach and landing preparation with ATC. Pilot not flying programmed the FMC and got performance data for landing at the divert airport. Pilot not flying contacted Operations and coordinated gate arrival. Pilot flying and pilot not flying discussed overweight landing considerations. [We] received vectors to visual final to Runway 1. Landing was uneventful. After landing we both heard a loud tone and were unable to determine the source. We later discovered it was the lavatory fire/smoke warning. Completed checklist and pulled circuit breaker. No fires noted. Upon arrival at the gate; pilot flying observed the cabin was still pressurized. [Pilot flying] directed pilot not flying to slowly open outflow valve to depressurize the cabin. Pilot not flying (me) had failed to open the outflow valve after the aircraft was below 1;000 FT MSL.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1035482
Time
Date	201209
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Climb
Flight Plan	IFR
Component
Aircraft Component	Pressurization Control System
Person 1
Function	Pilot Not Flying First Officer
Experience	Flight Crew Last 90 Days 205 Flight Crew Type 7200
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Maintenance

At FL270 a B737 cabin altitude warning horn sounded so an emergency was declared and the flight descended to 8;000 ft. On this flight and the previous flight the equip cooling off light illuminated indicating a lack of air flow.