|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||1201 To 1800|
|Locale Reference||navaid : jvl.ndb|
|Altitude||msl single value : 35000|
|Controlling Facilities||artcc : zmp.artcc|
|Operator||common carrier : air carrier|
|Make Model Name||B747-400|
|Operating Under FAR Part||Part 121|
|Flight Phase||cruise : level|
|Route In Use||enroute : direct|
|Affiliation||company : air carrier|
|Function||flight crew : first officer|
|Affiliation||company : air carrier|
|Function||flight crew : captain|
oversight : pic
|Anomaly||aircraft equipment problem : critical|
non adherence : published procedure
other anomaly other
|Independent Detector||aircraft equipment other aircraft equipment : cabin altitude indicator|
other flight crewa
other flight crewb
|Resolutory Action||flight crew : overcame equipment problem|
|Maintenance||performance deficiency : repair|
|Problem Areas||Flight Crew Human Performance|
Maintenance Human Performance
|Primary Problem||Flight Crew Human Performance|
The cabin pressurization rate had been fluctuating 500 FPM through flight and was documented in previous write-ups. Captain decided to troubleshoot and cycled outflow valves individually to manual then back. Upon cycling one of the valves, the outflow valves opened, causing the cabin to climb in excess of 9900 FPM. Cabin altitude reached around 11400 ft, according to the captain, before it became ctlable again in manual. The outflow valves were closed and the cabin dropped below 10000 ft, then the pressurization differential went to 9.0. Once the flight manual was consulted, the pressure controller was selected to 'a,' the valves placed in back into automatic, and normal pressure restored. This action was also noted to have been taken by a previous crew, in a jan/fri/01 write-up. The first officer's became aware of problem when the cabin began climbing excessively. At 10000 ft, one of the non flying first officer's directed the flying first officer to take control of the aircraft. The qrc was not executed, as it was felt that the cabin altitude control was quickly regained. Time from 6000 ft to 11400 ft was about 20 seconds, and time to restore below 10000 ft was about 40 seconds. The entire incident took about 5 mins. A descent was initiated with ATC while the outflow valves were in manual, and normal operations were restored with the cabin controller in 'a.'
Original NASA ASRS Text
Title: A B747-400 IN CRUISE AT FL350 THE CREW ATTEMPTED TO TROUBLESHOOT A CHRONIC PRESSURIZATION SYS AND LOST CABIN PRESSURE FOR ABOUT 40 SECONDS.
Narrative: THE CABIN PRESSURIZATION RATE HAD BEEN FLUCTUATING 500 FPM THROUGH FLT AND WAS DOCUMENTED IN PREVIOUS WRITE-UPS. CAPT DECIDED TO TROUBLESHOOT AND CYCLED OUTFLOW VALVES INDIVIDUALLY TO MANUAL THEN BACK. UPON CYCLING ONE OF THE VALVES, THE OUTFLOW VALVES OPENED, CAUSING THE CABIN TO CLB IN EXCESS OF 9900 FPM. CABIN ALT REACHED AROUND 11400 FT, ACCORDING TO THE CAPT, BEFORE IT BECAME CTLABLE AGAIN IN MANUAL. THE OUTFLOW VALVES WERE CLOSED AND THE CABIN DROPPED BELOW 10000 FT, THEN THE PRESSURIZATION DIFFERENTIAL WENT TO 9.0. ONCE THE FLT MANUAL WAS CONSULTED, THE PRESSURE CONTROLLER WAS SELECTED TO 'A,' THE VALVES PLACED IN BACK INTO AUTO, AND NORMAL PRESSURE RESTORED. THIS ACTION WAS ALSO NOTED TO HAVE BEEN TAKEN BY A PREVIOUS CREW, IN A JAN/FRI/01 WRITE-UP. THE FO'S BECAME AWARE OF PROB WHEN THE CABIN BEGAN CLBING EXCESSIVELY. AT 10000 FT, ONE OF THE NON FLYING FO'S DIRECTED THE FLYING FO TO TAKE CTL OF THE ACFT. THE QRC WAS NOT EXECUTED, AS IT WAS FELT THAT THE CABIN ALT CTL WAS QUICKLY REGAINED. TIME FROM 6000 FT TO 11400 FT WAS ABOUT 20 SECONDS, AND TIME TO RESTORE BELOW 10000 FT WAS ABOUT 40 SECONDS. THE ENTIRE INCIDENT TOOK ABOUT 5 MINS. A DSCNT WAS INITIATED WITH ATC WHILE THE OUTFLOW VALVES WERE IN MANUAL, AND NORMAL OPS WERE RESTORED WITH THE CABIN CONTROLLER IN 'A.'
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.