Narrative:

We experienced a slow loss of pressurization as we were descending out of FL350. The first indication was a flow light illumination, and at the time, since we were in the clear, we did not have anti-ice on. (The pressure output on both packs appeared within the normal range at the time.) at first glance the outflow valve appeared to be closed, but the cabin rate of climb was over 1500 FPM climb. At the time we were descending to FL240. Even though the cabin altitude indicator was rising slowly, I decided it would be best to wear our oxygen masks, and told first officer to tell ATC we were having trouble holding our cabin pressure and we needed a clearance to 14000 ft. I instructed the first officer to follow the 'cabin altitude warning/rapid depressurization' procedure while I flew the airplane. During this time we received clearance to descend to 14000 ft. Since the cabin was depressurizing slowly, and ATC had given us our desired altitude, I chose not to declare an emergency. By the time we were passing FL230, the first officer was trying to manually control the pressure in accordance to the procedure, since just prior to that time the automatic system had the outflow valve partially open. He could not get the cabin to descend. I felt he was a little slow in getting the procedure completed. During the descent the cabin rose to slightly above 11000 ft and I was able to get the airplane down fast enough to avoid the deployment of the passenger oxygen masks. During the descent I advised the flight attendants to be prepared to wear oxygen, because we were losing pressurization. We descended further to 10000 ft. At between 14000 ft and 10000 ft aircraft altitude, the first officer regained control of the cabin pressure manually and was able to begin a slow descent of the cabin altitude. The remainder of the flight was uneventful. Extra note: after we leveled off I noticed he did not manually completely close the outflow valve. We started getting pressure back after he figured the control out.

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Original NASA ASRS Text

Title: AN ACR HAS A PRESSURIZATION LOSS DURING DSCNT. CTL OF CABIN ALT IS REGAINED WITH PROVIDED MANUAL CTL PROC.

Narrative: WE EXPERIENCED A SLOW LOSS OF PRESSURIZATION AS WE WERE DSNDING OUT OF FL350. THE FIRST INDICATION WAS A FLOW LIGHT ILLUMINATION, AND AT THE TIME, SINCE WE WERE IN THE CLR, WE DID NOT HAVE ANTI-ICE ON. (THE PRESSURE OUTPUT ON BOTH PACKS APPEARED WITHIN THE NORMAL RANGE AT THE TIME.) AT FIRST GLANCE THE OUTFLOW VALVE APPEARED TO BE CLOSED, BUT THE CABIN RATE OF CLB WAS OVER 1500 FPM CLB. AT THE TIME WE WERE DSNDING TO FL240. EVEN THOUGH THE CABIN ALT INDICATOR WAS RISING SLOWLY, I DECIDED IT WOULD BE BEST TO WEAR OUR OXYGEN MASKS, AND TOLD FO TO TELL ATC WE WERE HAVING TROUBLE HOLDING OUR CABIN PRESSURE AND WE NEEDED A CLRNC TO 14000 FT. I INSTRUCTED THE FO TO FOLLOW THE 'CABIN ALT WARNING/RAPID DEPRESSURIZATION' PROC WHILE I FLEW THE AIRPLANE. DURING THIS TIME WE RECEIVED CLRNC TO DSND TO 14000 FT. SINCE THE CABIN WAS DEPRESSURIZING SLOWLY, AND ATC HAD GIVEN US OUR DESIRED ALT, I CHOSE NOT TO DECLARE AN EMER. BY THE TIME WE WERE PASSING FL230, THE FO WAS TRYING TO MANUALLY CTL THE PRESSURE IN ACCORDANCE TO THE PROC, SINCE JUST PRIOR TO THAT TIME THE AUTOMATIC SYS HAD THE OUTFLOW VALVE PARTIALLY OPEN. HE COULD NOT GET THE CABIN TO DSND. I FELT HE WAS A LITTLE SLOW IN GETTING THE PROC COMPLETED. DURING THE DSCNT THE CABIN ROSE TO SLIGHTLY ABOVE 11000 FT AND I WAS ABLE TO GET THE AIRPLANE DOWN FAST ENOUGH TO AVOID THE DEPLOYMENT OF THE PAX OXYGEN MASKS. DURING THE DSCNT I ADVISED THE FLT ATTENDANTS TO BE PREPARED TO WEAR OXYGEN, BECAUSE WE WERE LOSING PRESSURIZATION. WE DSNDED FURTHER TO 10000 FT. AT BTWN 14000 FT AND 10000 FT ACFT ALT, THE FO REGAINED CTL OF THE CABIN PRESSURE MANUALLY AND WAS ABLE TO BEGIN A SLOW DSCNT OF THE CABIN ALT. THE REMAINDER OF THE FLT WAS UNEVENTFUL. EXTRA NOTE: AFTER WE LEVELED OFF I NOTICED HE DID NOT MANUALLY COMPLETELY CLOSE THE OUTFLOW VALVE. WE STARTED GETTING PRESSURE BACK AFTER HE FIGURED THE CTL OUT.

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.