While climbing through high altitude, the cabin altitude warning horn advised that the cabin was cli...

Attributes
ACN	276071
Time
Date	199406
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : har
State Reference	PA
Altitude	msl bound lower : 18000 msl bound upper : 31000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zny tower : bos
Operator	common carrier : air carrier
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude descent other other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 15 flight time total : 10000
ASRS Report	276071
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
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 flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

During preflight, when the recall light was pressed, the left pack light illuminated. The discrepancy was entered in the logbook. Corrective action was taken by maintenance. Takeoff and climb were normal until approximately FL310. At that point, the cabin altitude warning horn began. The cabin altitude was approaching 10000 ft and climbing. Both packs were checked in automatic, both bleeds were checked open, and the outflow valve was selected manual and closed. I declared an emergency and received clearance to 14000 ft. The emergency checklists were completed during the descent. Descending through approximately FL200, the cabin began to descend. We requested level at FL180 where the cabin descended to 4000 ft and stabilized. Pressurization was switched to standby with normal operation continued in that mode. When the automatic pressurization mode selected, the cabin began climbing. With standby mode selected and operation normal, we reported the situation under control and climbed to FL240, proceeding on route to ind, our destination. We discovered that switching the right pack off caused the cabin to climb at 2000 FPM and greater. With left pack off, pressurization remained stable, indicating left pack was weak or inoperative. It was determined by maintenance, that a duct seal ruptured in the left air conditioning system between the air cycle machine and the water separator. The left pack was unable to supply to the pressurization system. The right pack was able to work at maximum at lower altitudes to maintain adequate pressurization.

Original NASA ASRS Text

Title: WHILE CLBING THROUGH HIGH ALT, THE CABIN ALT WARNING HORN ADVISED THAT THE CABIN WAS CLBING THROUGH 10000 FT. THE FLC DECLARED AN EMER TO ATC AND DSNDED TO FL180 BEFORE THE ACFT PRESSURIZATION WAS STABILIZED.

Narrative: DURING PREFLT, WHEN THE RECALL LIGHT WAS PRESSED, THE L PACK LIGHT ILLUMINATED. THE DISCREPANCY WAS ENTERED IN THE LOGBOOK. CORRECTIVE ACTION WAS TAKEN BY MAINT. TKOF AND CLB WERE NORMAL UNTIL APPROX FL310. AT THAT POINT, THE CABIN ALT WARNING HORN BEGAN. THE CABIN ALT WAS APCHING 10000 FT AND CLBING. BOTH PACKS WERE CHKED IN AUTO, BOTH BLEEDS WERE CHKED OPEN, AND THE OUTFLOW VALVE WAS SELECTED MANUAL AND CLOSED. I DECLARED AN EMER AND RECEIVED CLRNC TO 14000 FT. THE EMER CHKLISTS WERE COMPLETED DURING THE DSCNT. DSNDING THROUGH APPROX FL200, THE CABIN BEGAN TO DSND. WE REQUESTED LEVEL AT FL180 WHERE THE CABIN DSNDED TO 4000 FT AND STABILIZED. PRESSURIZATION WAS SWITCHED TO STANDBY WITH NORMAL OP CONTINUED IN THAT MODE. WHEN THE AUTO PRESSURIZATION MODE SELECTED, THE CABIN BEGAN CLBING. WITH STANDBY MODE SELECTED AND OP NORMAL, WE RPTED THE SIT UNDER CTL AND CLBED TO FL240, PROCEEDING ON RTE TO IND, OUR DEST. WE DISCOVERED THAT SWITCHING THE R PACK OFF CAUSED THE CABIN TO CLB AT 2000 FPM AND GREATER. WITH L PACK OFF, PRESSURIZATION REMAINED STABLE, INDICATING L PACK WAS WEAK OR INOP. IT WAS DETERMINED BY MAINT, THAT A DUCT SEAL RUPTURED IN THE L AIR CONDITIONING SYS BTWN THE AIR CYCLE MACHINE AND THE WATER SEPARATOR. THE L PACK WAS UNABLE TO SUPPLY TO THE PRESSURIZATION SYS. THE R PACK WAS ABLE TO WORK AT MAX AT LOWER ALTS TO MAINTAIN ADEQUATE PRESSURIZATION.

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.

While climbing through high altitude, the cabin altitude warning horn advised that the cabin was climbing through 10000 ft. The flight crew declared an emergency to ATC and descended to FL180 before the aircraft pressurization was stabilized.