Cabin pressure lost as aircraft climbs to 31000 ft. Descend land.

Attributes
ACN	249957
Time
Date	199308
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : ind
State Reference	IN
Altitude	msl bound lower : 31000 msl bound upper : 31000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau tower : arr
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute : on vectors enroute airway : j84
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 185 flight time total : 15750 flight time type : 675
ASRS Report	249957
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer pilot : cfi
Experience	flight time last 90 days : 155 flight time total : 7500 flight time type : 1300
ASRS Report	249955
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	none taken : unable other
Consequence	Other Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Noticed cabin altitude at 9000 ft after leveling at FL310. Tried manual pressurization control but could not get cabin to pressurize properly. The cabin continued a slow climb. We told center of the problem and made rapid descent to 10000 ft. When we reduced power for descent, the cabin altitude seemed to climb faster. The oxygen masks dropped at 14000 ft cabin altitude. At 10000 ft the cabin slowly pressurized and got down to about 3000 ft. The company advised us to land at ind to better accommodate the passenger. I briefed the passenger as to what occurred and there was no problem with the safety of the flight. I talked to maintenance later and was unofficially informed that an avionics cooling outflow valve stuck open preventing proper pressurization. We received no alerts as to any system malfunction. Supplemental information from acn 249955: our control over the pressurization valves got worse and we were forced to go to manual pressurization for the final segment into ind. At this point we got some complaints from passenger concerning their ears. Landed without incident with cabin altitude finally down to field elevation. Passenger's ears seemed to recover and we did not get any more complaints as they exited the aircraft.

Original NASA ASRS Text

Title: CABIN PRESSURE LOST AS ACFT CLBS TO 31000 FT. DSND LAND.

Narrative: NOTICED CABIN ALT AT 9000 FT AFTER LEVELING AT FL310. TRIED MANUAL PRESSURIZATION CTL BUT COULD NOT GET CABIN TO PRESSURIZE PROPERLY. THE CABIN CONTINUED A SLOW CLB. WE TOLD CTR OF THE PROB AND MADE RAPID DSCNT TO 10000 FT. WHEN WE REDUCED PWR FOR DSCNT, THE CABIN ALT SEEMED TO CLB FASTER. THE OXYGEN MASKS DROPPED AT 14000 FT CABIN ALT. AT 10000 FT THE CABIN SLOWLY PRESSURIZED AND GOT DOWN TO ABOUT 3000 FT. THE COMPANY ADVISED US TO LAND AT IND TO BETTER ACCOMMODATE THE PAX. I BRIEFED THE PAX AS TO WHAT OCCURRED AND THERE WAS NO PROB WITH THE SAFETY OF THE FLT. I TALKED TO MAINT LATER AND WAS UNOFFICIALLY INFORMED THAT AN AVIONICS COOLING OUTFLOW VALVE STUCK OPEN PREVENTING PROPER PRESSURIZATION. WE RECEIVED NO ALERTS AS TO ANY SYS MALFUNCTION. SUPPLEMENTAL INFORMATION FROM ACN 249955: OUR CTL OVER THE PRESSURIZATION VALVES GOT WORSE AND WE WERE FORCED TO GO TO MANUAL PRESSURIZATION FOR THE FINAL SEGMENT INTO IND. AT THIS POINT WE GOT SOME COMPLAINTS FROM PAX CONCERNING THEIR EARS. LANDED WITHOUT INCIDENT WITH CABIN ALT FINALLY DOWN TO FIELD ELEVATION. PAX'S EARS SEEMED TO RECOVER AND WE DID NOT GET ANY MORE COMPLAINTS AS THEY EXITED THE ACFT.

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.