<< >> NASA ASRS Report 515820, June 2001

B737 flight crew make an emergency descent after the cabin pressurization horn sounded that the cabin pressure was passing 10000 ft in altitude.

Attributes
ACN	515820
Time
Date	200106
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : phx.airport
State Reference	AZ
Altitude	msl single value : 28000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zab.artcc tower : lax.tower
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : enroute altitude change
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Experience	flight time last 90 days : 100 flight time total : 10000 flight time type : 4000
ASRS Report	515820
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : cabin press indicator bell other flight crewa other flight crewb
Resolutory Action	flight crew : overrode automation flight crew : declared emergency flight crew : overcame equipment problem other
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

While descending on arlin arrival to phx, we experienced a pressurization problem (gradual cabin decompression). The first indication of the problem was the 10000 ft cabin altitude warning that is identical to takeoff confign warning. Shortly thereafter, we saw the following warning lights: 'automatic pressurization failure' and 'off schedule descent.' we donned oxygen masks and accomplished cabin altitude rapid depressurization checklist as per our QRH. We regained pressurization immediately but continued our descent to 10000 ft MSL as a precautionary measure. When the first warning horn sounded I did not immediately realize we had a pressurization problem because the horn is the same as takeoff confign warning. Simulator training only covers rapid decompression, not gradual cabin decompression. Gradual cabin decompression is a more insidious emergency.

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Original NASA ASRS Text

Title: B737 FLC MAKE AN EMER DSCNT AFTER THE CABIN PRESSURIZATION HORN SOUNDED THAT THE CABIN PRESSURE WAS PASSING 10000 FT IN ALT.

Narrative: WHILE DSNDING ON ARLIN ARR TO PHX, WE EXPERIENCED A PRESSURIZATION PROB (GRADUAL CABIN DECOMPRESSION). THE FIRST INDICATION OF THE PROB WAS THE 10000 FT CABIN ALT WARNING THAT IS IDENTICAL TO TKOF CONFIGN WARNING. SHORTLY THEREAFTER, WE SAW THE FOLLOWING WARNING LIGHTS: 'AUTO PRESSURIZATION FAILURE' AND 'OFF SCHEDULE DSCNT.' WE DONNED OXYGEN MASKS AND ACCOMPLISHED CABIN ALT RAPID DEPRESSURIZATION CHKLIST AS PER OUR QRH. WE REGAINED PRESSURIZATION IMMEDIATELY BUT CONTINUED OUR DSCNT TO 10000 FT MSL AS A PRECAUTIONARY MEASURE. WHEN THE FIRST WARNING HORN SOUNDED I DID NOT IMMEDIATELY REALIZE WE HAD A PRESSURIZATION PROB BECAUSE THE HORN IS THE SAME AS TKOF CONFIGN WARNING. SIMULATOR TRAINING ONLY COVERS RAPID DECOMPRESSION, NOT GRADUAL CABIN DECOMPRESSION. GRADUAL CABIN DECOMPRESSION IS A MORE INSIDIOUS EMER.

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.