|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||0601 To 1200|
|Locale Reference||atc facility : sac|
|Altitude||msl bound lower : 25000|
msl bound upper : 32000
|Controlling Facilities||tower : den|
|Operator||common carrier : air carrier|
|Make Model Name||Large Transport, Low Wing, 3 Turbojet Eng|
|Flight Phase||climbout : intermediate altitude|
|Route In Use||enroute airway : j32|
|Affiliation||company : air carrier|
|Function||flight crew : captain|
oversight : pic
|Qualification||pilot : atp|
pilot : flight engineer
|Experience||flight time last 90 days : 150|
flight time total : 10800
flight time type : 1300
|Affiliation||company : air carrier|
|Function||flight crew : first officer|
|Qualification||pilot : flight engineer|
pilot : instrument
pilot : commercial
|Anomaly||aircraft equipment problem : critical|
|Independent Detector||aircraft equipment other aircraft equipment : unspecified|
|Resolutory Action||flight crew : overcame equipment problem|
flight crew : declared emergency
Departed sfo climbing through FL320 on way up to FL330 en route to msp. Cabin altitude horn sounded indicating cabin had exceeded 10000'. We notified center and requested lower. After second officer was unable to correct situation using abnormal procedures, we declared emergency and initiated descent. Cabin climb rate was arrested descending through FL250 and was descended through 10000' with the aircraft descending through FL200. Center requested we level at 16000' and we complied since cabin altitude was stabilized below 10000'. Cockpit crew donned masks immediately after horn had sounded. Passenger masks did not drop as cabin altitude never reached 14000'. We returned to sfo and maintenance determined that equipment cooling outflow valve failed to close at appropriate time during climb (2.2 diff pressure), causing excess air to be dumped overboard and subsequent cabin climb above selected altitude. Cabin rate of climb was so gradual, about 400-500 FPM, that it went unnoticed when it exceeded selected altitude. Since the first indication of a problem was the cabin altitude horn, only extreme vigilance of cabin pressure gauges could have prevented this occurrence. Nothing could have prevented the malfunction.
Original NASA ASRS Text
Title: ACR LGT EXPERIENCES PRESSURIZATION PROBLEMS IN CLIMB.
Narrative: DEPARTED SFO CLBING THROUGH FL320 ON WAY UP TO FL330 ENRTE TO MSP. CABIN ALT HORN SOUNDED INDICATING CABIN HAD EXCEEDED 10000'. WE NOTIFIED CENTER AND REQUESTED LOWER. AFTER S/O WAS UNABLE TO CORRECT SITUATION USING ABNORMAL PROCS, WE DECLARED EMER AND INITIATED DSNT. CABIN CLB RATE WAS ARRESTED DSNDING THROUGH FL250 AND WAS DSNDED THROUGH 10000' WITH THE ACFT DSNDING THROUGH FL200. CENTER REQUESTED WE LEVEL AT 16000' AND WE COMPLIED SINCE CABIN ALT WAS STABILIZED BELOW 10000'. COCKPIT CREW DONNED MASKS IMMEDIATELY AFTER HORN HAD SOUNDED. PAX MASKS DID NOT DROP AS CABIN ALT NEVER REACHED 14000'. WE RETURNED TO SFO AND MAINT DETERMINED THAT EQUIP COOLING OUTFLOW VALVE FAILED TO CLOSE AT APPROPRIATE TIME DURING CLB (2.2 DIFF PRESSURE), CAUSING EXCESS AIR TO BE DUMPED OVERBOARD AND SUBSEQUENT CABIN CLB ABOVE SELECTED ALT. CABIN RATE OF CLB WAS SO GRADUAL, ABOUT 400-500 FPM, THAT IT WENT UNNOTICED WHEN IT EXCEEDED SELECTED ALT. SINCE THE FIRST INDICATION OF A PROB WAS THE CABIN ALT HORN, ONLY EXTREME VIGILANCE OF CABIN PRESSURE GAUGES COULD HAVE PREVENTED THIS OCCURRENCE. NOTHING COULD HAVE PREVENTED THE MALFUNCTION.
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.