A B737-300 flight crew lost control of cabin pressure and got a cabin altitude warning horn. They re...

Attributes
ACN	798943
Time
Date	200808
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 35000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	descent : vacating altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 262
ASRS Report	798943
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	aircraft equipment other aircraft equipment : cabin alt warn horn other flight crewa
Resolutory Action	flight crew : exited adverse environment flight crew : overcame equipment problem
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Our cruise altitude was FL370. We received descent clearance to FL240. During our idle descent with engine anti-ice on; we got a cabin altitude warning horn descending through FL350. I noticed the cabin altitude was 11000 ft. We accomplished the QRH procedure for 'cabin altitude warning horn.' the first officer's oxygen mask microphone was intermittent. It had a short in the cord that could be corrected by holding the cord in a certain position. (It did test properly during the preflight inspection.) this made our communications somewhat challenging. I requested a further descent all the way down to 10000 ft. We had a difficult time controling the cabin altitude with the controller in manual. We never received any master caution or 'automatic fail' annunciations. The passenger cabin masks did not drop. We never declared an emergency because ATC approved our descent to 10000 ft without delay and I felt my immediate attention should be flying the aircraft and troubleshooting the problem. Once we were below 10000 ft; we tried the standby pressure controller and it was able to control the cabin much better than the manual controller. Landing was uneventful and maintenance discrepancies were written up. We swapped aircraft and continued our schedule.

Original NASA ASRS Text

Title: A B737-300 FLT CREW LOST CONTROL OF CABIN PRESSURE AND GOT A CABIN ALT WARNING HORN. THEY RECEIVED A LOWER ALT AND WERE ABLE TO CONTROL THE CABIN PRESSURE WITH THE STBY CONTROLLER.

Narrative: OUR CRUISE ALT WAS FL370. WE RECEIVED DSCNT CLRNC TO FL240. DURING OUR IDLE DSCNT WITH ENG ANTI-ICE ON; WE GOT A CABIN ALT WARNING HORN DSNDING THROUGH FL350. I NOTICED THE CABIN ALT WAS 11000 FT. WE ACCOMPLISHED THE QRH PROC FOR 'CABIN ALT WARNING HORN.' THE FO'S OXYGEN MASK MIKE WAS INTERMITTENT. IT HAD A SHORT IN THE CORD THAT COULD BE CORRECTED BY HOLDING THE CORD IN A CERTAIN POS. (IT DID TEST PROPERLY DURING THE PREFLT INSPECTION.) THIS MADE OUR COMS SOMEWHAT CHALLENGING. I REQUESTED A FURTHER DSCNT ALL THE WAY DOWN TO 10000 FT. WE HAD A DIFFICULT TIME CTLING THE CABIN ALT WITH THE CTLR IN MANUAL. WE NEVER RECEIVED ANY MASTER CAUTION OR 'AUTO FAIL' ANNUNCIATIONS. THE PAX CABIN MASKS DID NOT DROP. WE NEVER DECLARED AN EMER BECAUSE ATC APPROVED OUR DSCNT TO 10000 FT WITHOUT DELAY AND I FELT MY IMMEDIATE ATTN SHOULD BE FLYING THE ACFT AND TROUBLESHOOTING THE PROB. ONCE WE WERE BELOW 10000 FT; WE TRIED THE STANDBY PRESSURE CTLR AND IT WAS ABLE TO CTL THE CABIN MUCH BETTER THAN THE MANUAL CTLR. LNDG WAS UNEVENTFUL AND MAINT DISCREPANCIES WERE WRITTEN UP. WE SWAPPED ACFT AND CONTINUED OUR SCHEDULE.

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

A B737-300 flight crew lost control of cabin pressure and got a cabin altitude warning horn. They received a lower altitude and were able to control the cabin pressure with the stby controller.