A B737-300 crew, in cruise at FL350, experienced a cabin pressure loss when one of the 2 air conditi...

Attributes
ACN	556648
Time
Date	200208
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	intersection : bleuz
State Reference	MS
Altitude	msl single value : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : n/s
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 20 flight time total : 22000 flight time type : 13000
ASRS Report	556648
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 175 flight time total : 15000 flight time type : 500
ASRS Report	556501
Events
Anomaly	aircraft equipment problem : critical non adherence : company policies non adherence : published procedure non adherence other other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : cab alt warning horn other flight crewa other flight crewb
Resolutory Action	controller : provided flight assist flight crew : overcame equipment problem
Consequence	faa : reviewed incident with flight crew other
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

Cruising from bhm to msy at FL350. The flight attendants called and asked us to warm up the cabin. The first officer warmed up the cabin and turned off the gasper fan. Began a descent to FL240. After a short time, cabin altitude warning horn began to sound. Horn was silenced, cabin altitude was at 10000 ft, and differential pressure was indicated. Cabin was in a slight climb. Began emergency procedure for rapid depressurization. As the first officer was going for the QRH, 1 noticed that the r-hand air conditioning pack switch was in the 'off' position. It was placed 'on' and the cabin immediately began to descend. During this time we had notified ATC that we were requesting a lower altitude as we were experiencing a pressurization problem. They cleared us for further descent and asked if we were declaring an emergency. Our initial thought was to get the airplane below 14000 ft to keep the oxygen masks from deploying. Once the cabin was under control the descent was slowed and we replied that we were not declaring an emergency and our situation was under control. At no time did we descend below a cleared altitude or deviation from our assigned route. The sequence of events that led to this began when the first officer turned off the r-hand air conditioning pack switch instead of the gasper fan during cruise by mistake. The cabin slowly climbed during cruise and then slightly more once the power was reduced to begin the descent allowing it to finally reach 10000 ft setting off the warning horn. Supplemental information from acn 556501: in trying to regulate the cabin, I turned off the gasper and recirculation fan switches and evidently bumped or inadvertently placed the right pack switch to 'off.'

Original NASA ASRS Text

Title: A B737-300 CREW, IN CRUISE AT FL350, EXPERIENCED A CABIN PRESSURE LOSS WHEN ONE OF THE 2 AIR CONDITIONING PACKS WAS INADVERTENTLY TURNED OFF.

Narrative: CRUISING FROM BHM TO MSY AT FL350. THE FLT ATTENDANTS CALLED AND ASKED US TO WARM UP THE CABIN. THE FO WARMED UP THE CABIN AND TURNED OFF THE GASPER FAN. BEGAN A DSCNT TO FL240. AFTER A SHORT TIME, CABIN ALT WARNING HORN BEGAN TO SOUND. HORN WAS SILENCED, CABIN ALT WAS AT 10000 FT, AND DIFFERENTIAL PRESSURE WAS INDICATED. CABIN WAS IN A SLIGHT CLB. BEGAN EMER PROC FOR RAPID DEPRESSURIZATION. AS THE FO WAS GOING FOR THE QRH, 1 NOTICED THAT THE R-HAND AIR CONDITIONING PACK SWITCH WAS IN THE 'OFF' POS. IT WAS PLACED 'ON' AND THE CABIN IMMEDIATELY BEGAN TO DSND. DURING THIS TIME WE HAD NOTIFIED ATC THAT WE WERE REQUESTING A LOWER ALT AS WE WERE EXPERIENCING A PRESSURIZATION PROB. THEY CLRED US FOR FURTHER DSCNT AND ASKED IF WE WERE DECLARING AN EMER. OUR INITIAL THOUGHT WAS TO GET THE AIRPLANE BELOW 14000 FT TO KEEP THE OXYGEN MASKS FROM DEPLOYING. ONCE THE CABIN WAS UNDER CTL THE DSCNT WAS SLOWED AND WE REPLIED THAT WE WERE NOT DECLARING AN EMER AND OUR SIT WAS UNDER CTL. AT NO TIME DID WE DSND BELOW A CLRED ALT OR DEV FROM OUR ASSIGNED RTE. THE SEQUENCE OF EVENTS THAT LED TO THIS BEGAN WHEN THE FO TURNED OFF THE R-HAND AIR CONDITIONING PACK SWITCH INSTEAD OF THE GASPER FAN DURING CRUISE BY MISTAKE. THE CABIN SLOWLY CLBED DURING CRUISE AND THEN SLIGHTLY MORE ONCE THE PWR WAS REDUCED TO BEGIN THE DSCNT ALLOWING IT TO FINALLY REACH 10000 FT SETTING OFF THE WARNING HORN. SUPPLEMENTAL INFO FROM ACN 556501: IN TRYING TO REGULATE THE CABIN, I TURNED OFF THE GASPER AND RECIRCULATION FAN SWITCHES AND EVIDENTLY BUMPED OR INADVERTENTLY PLACED THE R PACK SWITCH TO 'OFF.'

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.

A B737-300 crew, in cruise at FL350, experienced a cabin pressure loss when one of the 2 air conditioning packs was inadvertently turned off.