An air carrier medium large transport had pressurization problems that required an immediate descent...

Attributes
ACN	336779
Time
Date	199605
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : inl
State Reference	MN
Altitude	msl bound lower : 29000 msl bound upper : 35000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zmp
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise other descent other 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 : 200 flight time total : 12000 flight time type : 4000
ASRS Report	336779
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude inflight encounter : weather 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 other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Aircraft

Narrative:

We had cabin pressure warning light and cabin slowly climbed to 10000 ft. Earlier, while cruising at FL350, engine EPR gauges climbed toward top of scale. (We were IMC and RAT temperature approximately minus 20 degree C.) turned on engine anti-ice and that corrected it. First officer was flying and he was concerned of wing ice so we turned on airfoil anti-ice. We did not appear to have any wing ice. We should have turned it off. We had severe thunderstorms across mn, doing a lot of deviating, light to moderate turbulence. St elmo's fire and workload was very heavy. Cabin altitude climbed very slowly (approximately 100 FPM) and we didn't feel any pressure bumps. When cabin pressure warning light came on, we donned oxygen masks and I knew right away the airfoil ice caused the cabin pressure to climb. I shut the airfoil ice off and closed the xfeeds. Then I accomplished first items on the loss of cabin pressure checklist. We started descent from FL350 and notified ATC as soon as possible we had a cabin pressure problem. We vacated FL350 and before ATC cleared us for lower, we were descending through approximately FL340. They cleared us to 8000 ft. The cabin pressure started descending right away and did not get above 10500 ft. Cabin oxygen masks did not deploy. A couple mins later, ATC asked us if we needed to declare an emergency or needed assistance. Cabin altitude was descending, we said negative and cabin pressure warning light went out shortly after that. We were off airways in remote area of northern mn. No traffic in area and ATC didn't sound concerned about us leaving FL350. We leveled at FL290 and continued to destination without further incident.

Original NASA ASRS Text

Title: AN ACR MLG HAD PRESSURIZATION PROBS THAT REQUIRED AN IMMEDIATE DSCNT.

Narrative: WE HAD CABIN PRESSURE WARNING LIGHT AND CABIN SLOWLY CLBED TO 10000 FT. EARLIER, WHILE CRUISING AT FL350, ENG EPR GAUGES CLBED TOWARD TOP OF SCALE. (WE WERE IMC AND RAT TEMP APPROX MINUS 20 DEG C.) TURNED ON ENG ANTI-ICE AND THAT CORRECTED IT. FO WAS FLYING AND HE WAS CONCERNED OF WING ICE SO WE TURNED ON AIRFOIL ANTI-ICE. WE DID NOT APPEAR TO HAVE ANY WING ICE. WE SHOULD HAVE TURNED IT OFF. WE HAD SEVERE TSTMS ACROSS MN, DOING A LOT OF DEVIATING, LIGHT TO MODERATE TURB. ST ELMO'S FIRE AND WORKLOAD WAS VERY HVY. CABIN ALT CLBED VERY SLOWLY (APPROX 100 FPM) AND WE DIDN'T FEEL ANY PRESSURE BUMPS. WHEN CABIN PRESSURE WARNING LIGHT CAME ON, WE DONNED OXYGEN MASKS AND I KNEW RIGHT AWAY THE AIRFOIL ICE CAUSED THE CABIN PRESSURE TO CLB. I SHUT THE AIRFOIL ICE OFF AND CLOSED THE XFEEDS. THEN I ACCOMPLISHED FIRST ITEMS ON THE LOSS OF CABIN PRESSURE CHKLIST. WE STARTED DSCNT FROM FL350 AND NOTIFIED ATC ASAP WE HAD A CABIN PRESSURE PROB. WE VACATED FL350 AND BEFORE ATC CLRED US FOR LOWER, WE WERE DSNDING THROUGH APPROX FL340. THEY CLRED US TO 8000 FT. THE CABIN PRESSURE STARTED DSNDING RIGHT AWAY AND DID NOT GET ABOVE 10500 FT. CABIN OXYGEN MASKS DID NOT DEPLOY. A COUPLE MINS LATER, ATC ASKED US IF WE NEEDED TO DECLARE AN EMER OR NEEDED ASSISTANCE. CABIN ALT WAS DSNDING, WE SAID NEGATIVE AND CABIN PRESSURE WARNING LIGHT WENT OUT SHORTLY AFTER THAT. WE WERE OFF AIRWAYS IN REMOTE AREA OF NORTHERN MN. NO TFC IN AREA AND ATC DIDN'T SOUND CONCERNED ABOUT US LEAVING FL350. WE LEVELED AT FL290 AND CONTINUED TO DEST WITHOUT FURTHER INCIDENT.

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.