Flight crew of an large transport air carrier aircraft failed to obtain lower altitude clearance until passed assigned altitude on descent due a loss of cabin pressurization.

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Attributes
ACN	248011
Time
Date	199307
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dik
State Reference	ND
Altitude	msl bound lower : 23000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other descent other
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 180 flight time total : 8000 flight time type : 4000
ASRS Report	248011
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 7000 flight time type : 4000
ASRS Report	247841
Events
Anomaly	aircraft equipment problem : critical altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

In cruise at FL330 aircraft cabin altitude started to climb. So was unable to control in automatic or manual and as cabin altitude went above 10000 ft, we asked for and received descent to FL290. Approaching FL290 we asked for lower and were eventually cleared to FL270 and FL230. The problem was as we approached each assigned altitude due to heavy radio talk we were unable to get a rapid clearance to a lower altitude and twice descended to 300 ft below assigned altitude. On the final descent the controller was slow to give us a lower altitude and we were unable to even declare an emergency due to radio congestion. With the cabin altitude still rising and approaching 12000 ft. I wanted to keep the aircraft descending, thus the gradual descent to slightly below assigned altitude. Just as we were finally able to get a word in on the radio and were going to declare and emergency, we got our final descent to FL230. Flight continued to destination (msp) as control of cabin was regained.

Original NASA ASRS Text

Title: FLC OF AN LGT ACR ACFT FAILED TO OBTAIN LOWER ALT CLRNC UNTIL PASSED ASSIGNED ALT ON DSCNT DUE A LOSS OF CABIN PRESSURIZATION.

Narrative: IN CRUISE AT FL330 ACFT CABIN ALT STARTED TO CLB. SO WAS UNABLE TO CTL IN AUTO OR MANUAL AND AS CABIN ALT WENT ABOVE 10000 FT, WE ASKED FOR AND RECEIVED DSCNT TO FL290. APCHING FL290 WE ASKED FOR LOWER AND WERE EVENTUALLY CLRED TO FL270 AND FL230. THE PROB WAS AS WE APCHED EACH ASSIGNED ALT DUE TO HVY RADIO TALK WE WERE UNABLE TO GET A RAPID CLRNC TO A LOWER ALT AND TWICE DSNDED TO 300 FT BELOW ASSIGNED ALT. ON THE FINAL DSCNT THE CTLR WAS SLOW TO GIVE US A LOWER ALT AND WE WERE UNABLE TO EVEN DECLARE AN EMER DUE TO RADIO CONGESTION. WITH THE CABIN ALT STILL RISING AND APCHING 12000 FT. I WANTED TO KEEP THE ACFT DSNDING, THUS THE GRADUAL DSCNT TO SLIGHTLY BELOW ASSIGNED ALT. JUST AS WE WERE FINALLY ABLE TO GET A WORD IN ON THE RADIO AND WERE GOING TO DECLARE AND EMER, WE GOT OUR FINAL DSCNT TO FL230. FLT CONTINUED TO DEST (MSP) AS CTL OF CABIN WAS REGAINED.

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.