Aircraft equipment problem depressurization.

Attributes
ACN	309779
Time
Date	199507
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : buf
State Reference	NY
Altitude	msl bound lower : 10000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zny
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 250 flight time total : 9000 flight time type : 3050
ASRS Report	309779
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : declared emergency flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

While in cruise at FL330, cabin altitude horn and cabin altitude warning light came on. The cabin had climbed rapidly to 13000 ft and we declared an emergency and initiated an emergency descent. Center cleared us to 10000 ft as we accomplished the loss of pressurization checklist. The outflow valve was open, so manual pressurization was selected and the outflow valve slowly started to close. When we leveled off at 10000 ft, the cabin pressure stabilized at 9000 ft and was controled in the manual mode until landing. Other than the rapid descent, no other priority handling was necessary and we continued on to boston with no other problems. Callback conversation with reporter revealed the following information: aircraft was dispatched with 1 air conditioning/pressurization pack inoperative and 1 cabin press controller inoperative. Apparently, either the 1 pack couldn't supply the pressure demand at the altitude or, a combination of that, and the 1 pressure controller malfunctioned. Aircraft began slowly depressurizing unbeknownst to the flight crew until the cabin altitude horn and warning light came on at 10000 ft cabin altitude. The outflow valve then went to full open, flight crew donned oxygen masks, declared an emergency and commenced emergency descent. First officer selected manual pressurization and was able to reestablish control of pressurization. Passenger oxygen masks did not deploy and, in fact, the entire cabin was unaware of the problem. A flight attendant came to the cockpit and seeing the flight crew with donned oxygen masks asked, 'is there a problem?'

Original NASA ASRS Text

Title: ACFT EQUIP PROB DEPRESSURIZATION.

Narrative: WHILE IN CRUISE AT FL330, CABIN ALT HORN AND CABIN ALT WARNING LIGHT CAME ON. THE CABIN HAD CLBED RAPIDLY TO 13000 FT AND WE DECLARED AN EMER AND INITIATED AN EMER DSCNT. CTR CLRED US TO 10000 FT AS WE ACCOMPLISHED THE LOSS OF PRESSURIZATION CHKLIST. THE OUTFLOW VALVE WAS OPEN, SO MANUAL PRESSURIZATION WAS SELECTED AND THE OUTFLOW VALVE SLOWLY STARTED TO CLOSE. WHEN WE LEVELED OFF AT 10000 FT, THE CABIN PRESSURE STABILIZED AT 9000 FT AND WAS CTLED IN THE MANUAL MODE UNTIL LNDG. OTHER THAN THE RAPID DSCNT, NO OTHER PRIORITY HANDLING WAS NECESSARY AND WE CONTINUED ON TO BOSTON WITH NO OTHER PROBS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ACFT WAS DISPATCHED WITH 1 AIR CONDITIONING/PRESSURIZATION PACK INOP AND 1 CABIN PRESS CTLR INOP. APPARENTLY, EITHER THE 1 PACK COULDN'T SUPPLY THE PRESSURE DEMAND AT THE ALT OR, A COMBINATION OF THAT, AND THE 1 PRESSURE CTLR MALFUNCTIONED. ACFT BEGAN SLOWLY DEPRESSURIZING UNBEKNOWNST TO THE FLC UNTIL THE CABIN ALT HORN AND WARNING LIGHT CAME ON AT 10000 FT CABIN ALT. THE OUTFLOW VALVE THEN WENT TO FULL OPEN, FLC DONNED OXYGEN MASKS, DECLARED AN EMER AND COMMENCED EMER DSCNT. FO SELECTED MANUAL PRESSURIZATION AND WAS ABLE TO REESTABLISH CTL OF PRESSURIZATION. PAX OXYGEN MASKS DID NOT DEPLOY AND, IN FACT, THE ENTIRE CABIN WAS UNAWARE OF THE PROB. A FLT ATTENDANT CAME TO THE COCKPIT AND SEEING THE FLC WITH DONNED OXYGEN MASKS ASKED, 'IS THERE A PROB?'

Data retrieved from NASA's ASRS site as of July 2007 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.