A B737-400 lost cabin pressurization during descent. An emergency was declared as the cabin altitude...

Attributes
ACN	702735
Time
Date	200607
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 30000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zzz.artcc tracon : zzz.tracon
Operator	common carrier : air carrier
Make Model Name	B737-400
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 200 flight time type : 4900
ASRS Report	702735
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : cabin alt warning horn other flight crewa
Resolutory Action	flight crew : declared emergency flight crew : took evasive action
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Shortly after we started our descent; it was noticed that the cabin was climbing at 1000 ft per min. I set the cabin pressurization control to standby in an attempt to regain control of the cabin. We ensured there were two packs on; two bleed air valves open and the outflow valve closed; but it kept climbing at 1000 ft per min. We then went to manual on the outflow valve to ensure that it was closed. The altitude warning horn sounded as I was arranging a rapid/emergency descent with ATC. We then started the emergency checklist with 'rapid depressurization/cabin altitude warning horn' followed by the emergency descent checklist. An emergency was declared with ATC at first contact for the descent and again with approach. We descended to 10000 ft initially and without allowing the cabin to climb above 10500 to 11000 ft; I believe. The emergency oxygen masks were not deployed in the cabin as the cabin altitude did not reach 14000 ft. The aircraft briefly exceeded V1 in the emergency descent. At 7000 ft; approach asked if we wanted to terminate the emergency and if we still needed emergency equipment. I elected to terminate the emergency after checking with the flight attendants for any injuries or problems. Everything in the cabin was all right and the passenger were unaware of the pressurization problem. An uneventful landing was made. Close monitoring of the system in question allowed us to mitigate the effects of the malfunction. Trying to contact all the necessary parties added to the task saturation problem.callback conversation with reporter revealed the following information: reporter stated that on a followup with maintenance; he learned the left engine pressure regulator was malfunctioning and the right air cycle machine was malfunctioning. Reporter also stated that although he guessed the cabin altitude warning horn would sound; the crew had a difficult time locating the horn silencing button.

Original NASA ASRS Text

Title: A B737-400 LOST CABIN PRESSURIZATION DURING DSCNT. AN EMER WAS DECLARED AS THE CABIN ALT WARNING HORN SOUNDED; BUT THE MASKS DID NOT DEPLOY.

Narrative: SHORTLY AFTER WE STARTED OUR DSCNT; IT WAS NOTICED THAT THE CABIN WAS CLBING AT 1000 FT PER MIN. I SET THE CABIN PRESSURIZATION CTL TO STANDBY IN AN ATTEMPT TO REGAIN CTL OF THE CABIN. WE ENSURED THERE WERE TWO PACKS ON; TWO BLEED AIR VALVES OPEN AND THE OUTFLOW VALVE CLOSED; BUT IT KEPT CLBING AT 1000 FT PER MIN. WE THEN WENT TO MANUAL ON THE OUTFLOW VALVE TO ENSURE THAT IT WAS CLOSED. THE ALT WARNING HORN SOUNDED AS I WAS ARRANGING A RAPID/EMER DSCNT WITH ATC. WE THEN STARTED THE EMER CHKLIST WITH 'RAPID DEPRESSURIZATION/CABIN ALT WARNING HORN' FOLLOWED BY THE EMER DSCNT CHKLIST. AN EMER WAS DECLARED WITH ATC AT FIRST CONTACT FOR THE DSCNT AND AGAIN WITH APCH. WE DSNDED TO 10000 FT INITIALLY AND WITHOUT ALLOWING THE CABIN TO CLB ABOVE 10500 TO 11000 FT; I BELIEVE. THE EMER OXYGEN MASKS WERE NOT DEPLOYED IN THE CABIN AS THE CABIN ALT DID NOT REACH 14000 FT. THE ACFT BRIEFLY EXCEEDED V1 IN THE EMER DSCNT. AT 7000 FT; APCH ASKED IF WE WANTED TO TERMINATE THE EMER AND IF WE STILL NEEDED EMER EQUIP. I ELECTED TO TERMINATE THE EMER AFTER CHKING WITH THE FLT ATTENDANTS FOR ANY INJURIES OR PROBS. EVERYTHING IN THE CABIN WAS ALL RIGHT AND THE PAX WERE UNAWARE OF THE PRESSURIZATION PROB. AN UNEVENTFUL LNDG WAS MADE. CLOSE MONITORING OF THE SYSTEM IN QUESTION ALLOWED US TO MITIGATE THE EFFECTS OF THE MALFUNCTION. TRYING TO CONTACT ALL THE NECESSARY PARTIES ADDED TO THE TASK SATURATION PROB.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT ON A FOLLOWUP WITH MAINT; HE LEARNED THE L ENG PRESSURE REGULATOR WAS MALFUNCTIONING AND THE R AIR CYCLE MACHINE WAS MALFUNCTIONING. RPTR ALSO STATED THAT ALTHOUGH HE GUESSED THE CABIN ALT WARNING HORN WOULD SOUND; THE CREW HAD A DIFFICULT TIME LOCATING THE HORN SILENCING BUTTON.

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.

A B737-400 lost cabin pressurization during descent. An emergency was declared as the cabin altitude warning horn sounded; but the masks did not deploy.