An air carrier crew descended without clearance while trying to control the cabin pressure.

Attributes
ACN	233685
Time
Date	199302
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : grb
State Reference	WI
Altitude	msl bound lower : 28000 msl bound upper : 29000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zmp tower : pwm
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other descent other other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp pilot : cfi
Experience	flight time last 90 days : 180 flight time total : 10000 flight time type : 7000
ASRS Report	233685
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 140 flight time total : 10000 flight time type : 6500
ASRS Report	234102
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment flight crew : declared emergency flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

At FL290, automatic cabin pressure controller malfunctioned. Cabin climbed rapidly to about 9000 ft. We went to manual and started a descent. Descent was started before we could tell ATC (because of congestion on frequency) that we had a cabin pressure problem. At FL280, first officer got control of the cabin (stopped it before 10000 ft). At the same time, we advised ATC of our problem and they cleared us to 13000 ft. No traffic conflict. Supplemental information from acn 234102: aircraft had previous problem with pressurization.

Original NASA ASRS Text

Title: AN ACR CREW DSNDED WITHOUT CLRNC WHILE TRYING TO CTL THE CABIN PRESSURE.

Narrative: AT FL290, AUTO CABIN PRESSURE CTLR MALFUNCTIONED. CABIN CLBED RAPIDLY TO ABOUT 9000 FT. WE WENT TO MANUAL AND STARTED A DSCNT. DSCNT WAS STARTED BEFORE WE COULD TELL ATC (BECAUSE OF CONGESTION ON FREQ) THAT WE HAD A CABIN PRESSURE PROB. AT FL280, FO GOT CTL OF THE CABIN (STOPPED IT BEFORE 10000 FT). AT THE SAME TIME, WE ADVISED ATC OF OUR PROB AND THEY CLRED US TO 13000 FT. NO TFC CONFLICT. SUPPLEMENTAL INFO FROM ACN 234102: ACFT HAD PREVIOUS PROB WITH PRESSURIZATION.

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.