MD80 cabin altitude warning activated. Flight crew descended and regained control of cabin altitude.

Attributes
ACN	755948
Time
Date	200709
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 34000
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	755948
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : cabin alt alert other flight crewa
Resolutory Action	flight crew : exited adverse environment flight crew : overcame equipment problem
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

About 1 hour after a step climb to FL340; we received an aural warning and a red cabin altitude alert. We donned our oxygen masks; first officer started the cabin altitude warning procedure in the QRH; the cabin altitude showed 10000 ft and the cabin differential of 7 psi. At the same time we requested FL240 to see if we could keep the cabin pressure below 10000 ft with the deferential we had. As we descended the cabin descended but the cabin differential continued to decrease. At that point we requested 16000 ft. As first officer accomplished the QRH procedure; he established control of the cabin with manual control of the outflow valve. Cabin altitude control was gained as we descended through FL180. We leveled off at 16000 ft. After confirming that we had positive control of the cabin; I elected to climb to FL180 and continue to landing at destination. At this point we were about 180 mi out and about 20 mins from landing. The rest of the flight was without incident.

Original NASA ASRS Text

Title: MD80 CABIN ALT WARNING ACTIVATED. FLT CREW DESCENDED AND REGAINED CONTROL OF CABIN ALT.

Narrative: ABOUT 1 HR AFTER A STEP CLB TO FL340; WE RECEIVED AN AURAL WARNING AND A RED CABIN ALT ALERT. WE DONNED OUR OXYGEN MASKS; FO STARTED THE CABIN ALT WARNING PROC IN THE QRH; THE CABIN ALT SHOWED 10000 FT AND THE CABIN DIFFERENTIAL OF 7 PSI. AT THE SAME TIME WE REQUESTED FL240 TO SEE IF WE COULD KEEP THE CABIN PRESSURE BELOW 10000 FT WITH THE DEFERENTIAL WE HAD. AS WE DSNDED THE CABIN DSNDED BUT THE CABIN DIFFERENTIAL CONTINUED TO DECREASE. AT THAT POINT WE REQUESTED 16000 FT. AS FO ACCOMPLISHED THE QRH PROC; HE ESTABLISHED CTL OF THE CABIN WITH MANUAL CTL OF THE OUTFLOW VALVE. CABIN ALT CTL WAS GAINED AS WE DSNDED THROUGH FL180. WE LEVELED OFF AT 16000 FT. AFTER CONFIRMING THAT WE HAD POSITIVE CTL OF THE CABIN; I ELECTED TO CLB TO FL180 AND CONTINUE TO LNDG AT DEST. AT THIS POINT WE WERE ABOUT 180 MI OUT AND ABOUT 20 MINS FROM LNDG. THE REST OF THE FLT WAS WITHOUT INCIDENT.

Data retrieved from NASA's ASRS site as of January 2009 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.