An air carrier widebody transport suffers a slow loss of cabin pressure. The flight crew fails to no...

Attributes
ACN	398926
Time
Date	199804
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : elp
State Reference	TX
Altitude	msl bound lower : 17000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zhu
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 70 flight time total : 12000 flight time type : 1100
ASRS Report	398926
Person 2
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : flight engineer pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical non adherence other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : exited adverse environment
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

After 1 hour cruise at FL330 crew observed cabin altitude warning horn and light (red). Performed loss of pressurization emergency checklist and requested immediate descent. ATC provided immediate clearance to FL190. Immediately prior and during descent, observed cabin rate of climb at +200 FPM. Cabin outflow valve position fully closed. Automatic, standby, and manual modes of cabin pressure control could not close cabin control valve any more, valve indicated fully closed. All 3 pack pressures, temperatures, and flow indications normal. Descending through FL200, observed cabin rate indicating 200 FPM descent. Cabin slowly repressurized, and requested 17000 ft cruise altitude. Descended cabin to 4000 ft and continued approximately 1 hour to destination. No obvious structural failure, ie, noise, door warning, or pack failure was observed. Loss of cabin pressurization was so gradual that no ear equalization discomfort was noticed. During cruise at 17000 ft and descent to landing, air flow into cabin was very weak, ie, no flow at eyeball outlets and outflow valve remained almost completely closed. During event, services of a deadheading company pilot were valuable in observing/collecting cabin data. CRM was utilized to great advantage for safe outcome.

Original NASA ASRS Text

Title: AN ACR WDB SUFFERS A SLOW LOSS OF CABIN PRESSURE. THE FLC FAILS TO NOTE THIS UNTIL THE ALT WARNING ALERT AND RED CAUTION LIGHT TELLS THEM THAT SOMETHING IS WRONG.

Narrative: AFTER 1 HR CRUISE AT FL330 CREW OBSERVED CABIN ALT WARNING HORN AND LIGHT (RED). PERFORMED LOSS OF PRESSURIZATION EMER CHKLIST AND REQUESTED IMMEDIATE DSCNT. ATC PROVIDED IMMEDIATE CLRNC TO FL190. IMMEDIATELY PRIOR AND DURING DSCNT, OBSERVED CABIN RATE OF CLB AT +200 FPM. CABIN OUTFLOW VALVE POS FULLY CLOSED. AUTO, STANDBY, AND MANUAL MODES OF CABIN PRESSURE CTL COULD NOT CLOSE CABIN CTL VALVE ANY MORE, VALVE INDICATED FULLY CLOSED. ALL 3 PACK PRESSURES, TEMPS, AND FLOW INDICATIONS NORMAL. DSNDING THROUGH FL200, OBSERVED CABIN RATE INDICATING 200 FPM DSCNT. CABIN SLOWLY REPRESSURIZED, AND REQUESTED 17000 FT CRUISE ALT. DSNDED CABIN TO 4000 FT AND CONTINUED APPROX 1 HR TO DEST. NO OBVIOUS STRUCTURAL FAILURE, IE, NOISE, DOOR WARNING, OR PACK FAILURE WAS OBSERVED. LOSS OF CABIN PRESSURIZATION WAS SO GRADUAL THAT NO EAR EQUALIZATION DISCOMFORT WAS NOTICED. DURING CRUISE AT 17000 FT AND DSCNT TO LNDG, AIR FLOW INTO CABIN WAS VERY WEAK, IE, NO FLOW AT EYEBALL OUTLETS AND OUTFLOW VALVE REMAINED ALMOST COMPLETELY CLOSED. DURING EVENT, SVCS OF A DEADHEADING COMPANY PLT WERE VALUABLE IN OBSERVING/COLLECTING CABIN DATA. CRM WAS UTILIZED TO GREAT ADVANTAGE FOR SAFE OUTCOME.

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.

An air carrier widebody transport suffers a slow loss of cabin pressure. The flight crew fails to note this until the altitude warning alert and red caution light tells them that something is wrong.