A B737-300 lost cabin pressurization at 33000 ft, resulting in an emergency descent and oxygen mask ...

Attributes
ACN	599914
Time
Date	200311
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ehf.airport
State Reference	CA
Altitude	msl single value : 32000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude climbout : vacating altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 210 flight time total : 19000 flight time type : 11200
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 : landed as precaution flight crew : overcame equipment problem flight crew : exited adverse environment flight crew : took precautionary avoidance action other
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Passing 32000 ft, climbing to 33000 ft, cabin altitude warning activated. Cabin altitude confirmed to be 10000 ft and climbing. Pressurization control panel confirmed to be set correctly. Full face oxygen masks were donned at beginning of warning and began fogging immediately. Mask was set to emergency to provide positive airflow. Fogging persisted. Qrc (quick reference checklist) was re-reviewed followed by QRH. During checklist it was noted that the pressurization panel had not 'automatic-failed' and had not defaulted to standby. At this point the cabin altitude was at 15000 ft. Standby was selected, but situation was deteriorating quickly and manual pressurization was selected. Flight attendants were notified of impending rapid descent and passenger masks were deployed manually (electrically). ATC was advised of descent and descent commenced. Decision was made to return to smf to reduce fuel load and minimize overweight landing. Obstacles to the smooth transition into the descent procedure was the pressurization panel not going into the automatic-fail mode and the fogging of the full-face oxygen masks.

Original NASA ASRS Text

Title: A B737-300 LOST CABIN PRESSURIZATION AT 33000 FT, RESULTING IN AN EMER DSCNT AND OXYGEN MASK DEPLOYMENT.

Narrative: PASSING 32000 FT, CLBING TO 33000 FT, CABIN ALT WARNING ACTIVATED. CABIN ALT CONFIRMED TO BE 10000 FT AND CLBING. PRESSURIZATION CTL PANEL CONFIRMED TO BE SET CORRECTLY. FULL FACE OXYGEN MASKS WERE DONNED AT BEGINNING OF WARNING AND BEGAN FOGGING IMMEDIATELY. MASK WAS SET TO EMER TO PROVIDE POSITIVE AIRFLOW. FOGGING PERSISTED. QRC (QUICK REF CHKLIST) WAS RE-REVIEWED FOLLOWED BY QRH. DURING CHKLIST IT WAS NOTED THAT THE PRESSURIZATION PANEL HAD NOT 'AUTO-FAILED' AND HAD NOT DEFAULTED TO STANDBY. AT THIS POINT THE CABIN ALT WAS AT 15000 FT. STANDBY WAS SELECTED, BUT SIT WAS DETERIORATING QUICKLY AND MANUAL PRESSURIZATION WAS SELECTED. FLT ATTENDANTS WERE NOTIFIED OF IMPENDING RAPID DSCNT AND PAX MASKS WERE DEPLOYED MANUALLY (ELECTRICALLY). ATC WAS ADVISED OF DSCNT AND DSCNT COMMENCED. DECISION WAS MADE TO RETURN TO SMF TO REDUCE FUEL LOAD AND MINIMIZE OVERWT LNDG. OBSTACLES TO THE SMOOTH TRANSITION INTO THE DSCNT PROC WAS THE PRESSURIZATION PANEL NOT GOING INTO THE AUTO-FAIL MODE AND THE FOGGING OF THE FULL-FACE OXYGEN MASKS.

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 lost cabin pressurization at 33000 ft, resulting in an emergency descent and oxygen mask deployment.