Slow depressurization of aircraft resulting in loss of pressurization control.

Attributes
ACN	100409
Time
Date	198812
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : orf
State Reference	VA
Altitude	msl bound lower : 10000 msl bound upper : 39000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : second officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 150 flight time total : 2200 flight time type : 150
ASRS Report	100409
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : declared emergency none taken : unable other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

While level at FL390, cabin pressurization warning horn went off, cabin pressurization climbing at 500 FPM past 10000'. Crew members put on oxygen, initiated appropriate emergency procedures and descended to 10000' MSL. Pressurization controller failed to function in the automatic, manual AC/dc, and standby modes. When aircraft was level at 10000' the manual dc mode of controller maintained cabin pressurization normally. Aircraft returned to airport of origin for repairs. Rest of flight uneventful.

Original NASA ASRS Text

Title: SLOW DEPRESSURIZATION OF ACFT RESULTING IN LOSS OF PRESSURIZATION CONTROL.

Narrative: WHILE LEVEL AT FL390, CABIN PRESSURIZATION WARNING HORN WENT OFF, CABIN PRESSURIZATION CLIMBING AT 500 FPM PAST 10000'. CREW MEMBERS PUT ON OXYGEN, INITIATED APPROPRIATE EMER PROCEDURES AND DESCENDED TO 10000' MSL. PRESSURIZATION CTLR FAILED TO FUNCTION IN THE AUTOMATIC, MANUAL AC/DC, AND STANDBY MODES. WHEN ACFT WAS LEVEL AT 10000' THE MANUAL DC MODE OF CTLR MAINTAINED CABIN PRESSURIZATION NORMALLY. ACFT RETURNED TO ARPT OF ORIGIN FOR REPAIRS. REST OF FLT UNEVENTFUL.

Data retrieved from NASA's ASRS site as of August 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.