Air carrier medium large transport unable to maintain cabin pressure when operating on 1 pack. Aircraft descends to 15000' where pressurization was restored and then flight descended to 11000' and continued to destination.

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Attributes
ACN	148529
Time
Date	199006
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : slt
State Reference	PA
Altitude	msl bound lower : 11000 msl bound upper : 25000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob
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 pilot : commercial
Experience	flight time last 90 days : 200 flight time total : 10000 flight time type : 7000
ASRS Report	148529
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : declared emergency flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

Flight was operating with 1 air conditioning pack. Shortly after leveling off at FL250 the cabin pressure annunciator light illuminated and the cabin pressure gauge indicated the cabin pressure was at 10000' and was climbing at 500 FPM. I declared an emergency, and descended to 11000'. Cabin pressure quickly returned to normal pressurization schedule once below 15000'. Center did not indicate any traffic conflicts as a result of our descent. After the cabin pressure descended below 10000', I terminated the emergency and continued to our destination at 11000'.

Original NASA ASRS Text

Title: ACR MLG UNABLE TO MAINTAIN CABIN PRESSURE WHEN OPERATING ON 1 PACK. ACFT DESCENDS TO 15000' WHERE PRESSURIZATION WAS RESTORED AND THEN FLT DESCENDED TO 11000' AND CONTINUED TO DESTINATION.

Narrative: FLT WAS OPERATING WITH 1 AIR CONDITIONING PACK. SHORTLY AFTER LEVELING OFF AT FL250 THE CABIN PRESSURE ANNUNCIATOR LIGHT ILLUMINATED AND THE CABIN PRESSURE GAUGE INDICATED THE CABIN PRESSURE WAS AT 10000' AND WAS CLBING AT 500 FPM. I DECLARED AN EMER, AND DSNDED TO 11000'. CABIN PRESSURE QUICKLY RETURNED TO NORMAL PRESSURIZATION SCHEDULE ONCE BELOW 15000'. CENTER DID NOT INDICATE ANY TFC CONFLICTS AS A RESULT OF OUR DSNT. AFTER THE CABIN PRESSURE DSNDED BELOW 10000', I TERMINATED THE EMER AND CONTINUED TO OUR DEST AT 11000'.

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.