Emergency declared by medium large transport when cabin pressure control is lost.

Attributes
ACN	252120
Time
Date	199309
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : fmg
State Reference	NV
Altitude	msl bound lower : 13000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise 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 : 70 flight time total : 13700 flight time type : 8200
ASRS Report	252120
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 240 flight time total : 3850 flight time type : 1840
ASRS Report	252358
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : declared emergency flight crew : exited adverse environment other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

After level-off at cruise altitude of FL330, throttles retarded for mach cruise, simultaneously cabin began major excursions (plus/minus 2000 FPM). A descent was requested and normal descent rate started (to FL270). Cabin continued a slow climb and it became obvious that cabin would soon pas 10000 ft, emergency declared, and rapid descent begun. Unable to control cabin (stop the cabin from climbing) in manual pressurization as cabin continued to climb. Cabin reached 13000 ft. We manually deployed oxygen masks for passenger and flight attendants. Flight descended to minimum en route altitude of 13000 and diverted to slc. Normal landing was made. No passenger hurt or injured. Maintenance personnel discovered that the 'second' cabin controller had failed (the aircraft has 2 identical controllers -- the other controller had been MEL'ed 6 days ago). The manual controller failed to operate properly because some duct insulation had jammed in the dump valve also (unknown if it was jammed before, or because of the other second controller failure). The aircraft is rotated through major overnight maintenance only once in every 7 days and was scheduled for repair to MEL'ed controller on the following day -- 1 day after my problem!

Original NASA ASRS Text

Title: EMER DECLARED BY MLG WHEN CABIN PRESSURE CTL IS LOST.

Narrative: AFTER LEVEL-OFF AT CRUISE ALT OF FL330, THROTTLES RETARDED FOR MACH CRUISE, SIMULTANEOUSLY CABIN BEGAN MAJOR EXCURSIONS (PLUS/MINUS 2000 FPM). A DSCNT WAS REQUESTED AND NORMAL DSCNT RATE STARTED (TO FL270). CABIN CONTINUED A SLOW CLB AND IT BECAME OBVIOUS THAT CABIN WOULD SOON PAS 10000 FT, EMER DECLARED, AND RAPID DSCNT BEGUN. UNABLE TO CTL CABIN (STOP THE CABIN FROM CLBING) IN MANUAL PRESSURIZATION AS CABIN CONTINUED TO CLB. CABIN REACHED 13000 FT. WE MANUALLY DEPLOYED OXYGEN MASKS FOR PAX AND FLT ATTENDANTS. FLT DSNDED TO MINIMUM ENRTE ALT OF 13000 AND DIVERTED TO SLC. NORMAL LNDG WAS MADE. NO PAX HURT OR INJURED. MAINT PERSONNEL DISCOVERED THAT THE 'SECOND' CABIN CTLR HAD FAILED (THE ACFT HAS 2 IDENTICAL CTLRS -- THE OTHER CTLR HAD BEEN MEL'ED 6 DAYS AGO). THE MANUAL CTLR FAILED TO OPERATE PROPERLY BECAUSE SOME DUCT INSULATION HAD JAMMED IN THE DUMP VALVE ALSO (UNKNOWN IF IT WAS JAMMED BEFORE, OR BECAUSE OF THE OTHER SECOND CTLR FAILURE). THE ACFT IS ROTATED THROUGH MAJOR OVERNIGHT MAINT ONLY ONCE IN EVERY 7 DAYS AND WAS SCHEDULED FOR REPAIR TO MEL'ED CTLR ON THE FOLLOWING DAY -- 1 DAY AFTER MY 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.