Air carrier medium large transport had pressurization problems at cruise altitude FL350.

Attributes
ACN	85257
Time
Date	198804
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : den
State Reference	CO
Altitude	msl bound lower : 35000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
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 : 250 flight time total : 18300
ASRS Report	85257
Person 2
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

We were at 35000' when I decided to adjust the cabin temperature to a lower setting. The right air conditioning pack tripped. Normally the remaining left pack will hold the pressurization system. However, this time it didn't. The cabin started up at a rapid rate and I was finally able to regain control of the cabin at 12000'. Automatic, standby or manual control was fruitless until I could get the right pack back on the line. I then requested and got a clearance from ATC to descend to a lower altitude. Center was very helpful and passed on information to the next sectors on our situation. We received additional lower altitudes in order to get our cabin to field elevation altitude. Because our forward outflow valve wouldn't close we could not get full pressure differential. I just want to say again that cooperation with ATC was excellent. The approach and landing came off fine and we didn't drop the masks.

Original NASA ASRS Text

Title: ACR MLG HAD PRESSURIZATION PROBLEMS AT CRUISE ALT FL350.

Narrative: WE WERE AT 35000' WHEN I DECIDED TO ADJUST THE CABIN TEMP TO A LOWER SETTING. THE RIGHT AIR CONDITIONING PACK TRIPPED. NORMALLY THE REMAINING LEFT PACK WILL HOLD THE PRESSURIZATION SYS. HOWEVER, THIS TIME IT DIDN'T. THE CABIN STARTED UP AT A RAPID RATE AND I WAS FINALLY ABLE TO REGAIN CTL OF THE CABIN AT 12000'. AUTO, STANDBY OR MANUAL CTL WAS FRUITLESS UNTIL I COULD GET THE RIGHT PACK BACK ON THE LINE. I THEN REQUESTED AND GOT A CLRNC FROM ATC TO DSND TO A LOWER ALT. CENTER WAS VERY HELPFUL AND PASSED ON INFO TO THE NEXT SECTORS ON OUR SITUATION. WE RECEIVED ADDITIONAL LOWER ALTS IN ORDER TO GET OUR CABIN TO FIELD ELEVATION ALT. BECAUSE OUR FORWARD OUTFLOW VALVE WOULDN'T CLOSE WE COULD NOT GET FULL PRESSURE DIFFERENTIAL. I JUST WANT TO SAY AGAIN THAT COOPERATION WITH ATC WAS EXCELLENT. THE APCH AND LNDG CAME OFF FINE AND WE DIDN'T DROP THE MASKS.

Data retrieved from NASA's ASRS site as of August 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.