Loss of pressurization requires an emergency descent.

Attributes
ACN	290607
Time
Date	199411
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : alb airport : swf
State Reference	NY
Altitude	msl bound lower : 35000 msl bound upper : 35000
Aircraft 1
Controlling Facilities	artcc : zbw
Operator	general aviation : corporate
Make Model Name	Cessna Citation Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	cruise other other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : instrument
Experience	flight time last 90 days : 60 flight time total : 15500 flight time type : 7000
ASRS Report	290607
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : exited adverse environment flight crew : declared emergency none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

Crew noticed a momentary 'acm ejector on' light on the annunciator panel. Also, a fluctuating cabin rate of climb indicator plus/minus 400 ft. The cabin altitude was at 9000 ft and holding. It should have been 5000 ft plus/minus. The captain had the first officer go on oxygen as a precaution, called for checklist and requested descent from ZBW. The aircraft, a C-550, was cleared to 24000 ft. ATC was notified this was a precautionary descent due to pressurization problems. ATC cleared us to 11000 ft. Passing approximately 34000 ft, the cabin rate went to 3000 to 400 FPM climb and was uncontrollable. The cabin passed 10000 ft. Master warn activated 'cabin over 10000 ft' annunciator came on -- and automatic mask deploy on cabin activated. An emergency descent was carried out -- transponder was put on 7700 -- ATC cleared aircraft to 8000 ft. The aircraft was leveled at 8000 ft and the trip was continued to destination kswf in the low level structure as it was only 80 NM ahead and a cessna citation maintenance facility was at the field. Cessna found a 10 ohm leak to ground on the squat switch and one outflow valve that was leaking beyond specifications. We also replaced the pressurization controller as a precaution.

Original NASA ASRS Text

Title: LOSS OF PRESSURIZATION REQUIRES AN EMER DSCNT.

Narrative: CREW NOTICED A MOMENTARY 'ACM EJECTOR ON' LIGHT ON THE ANNUNCIATOR PANEL. ALSO, A FLUCTUATING CABIN RATE OF CLB INDICATOR PLUS/MINUS 400 FT. THE CABIN ALT WAS AT 9000 FT AND HOLDING. IT SHOULD HAVE BEEN 5000 FT PLUS/MINUS. THE CAPT HAD THE FO GO ON OXYGEN AS A PRECAUTION, CALLED FOR CHKLIST AND REQUESTED DSCNT FROM ZBW. THE ACFT, A C-550, WAS CLRED TO 24000 FT. ATC WAS NOTIFIED THIS WAS A PRECAUTIONARY DSCNT DUE TO PRESSURIZATION PROBS. ATC CLRED US TO 11000 FT. PASSING APPROX 34000 FT, THE CABIN RATE WENT TO 3000 TO 400 FPM CLB AND WAS UNCTLABLE. THE CABIN PASSED 10000 FT. MASTER WARN ACTIVATED 'CABIN OVER 10000 FT' ANNUNCIATOR CAME ON -- AND AUTO MASK DEPLOY ON CABIN ACTIVATED. AN EMER DSCNT WAS CARRIED OUT -- XPONDER WAS PUT ON 7700 -- ATC CLRED ACFT TO 8000 FT. THE ACFT WAS LEVELED AT 8000 FT AND THE TRIP WAS CONTINUED TO DEST KSWF IN THE LOW LEVEL STRUCTURE AS IT WAS ONLY 80 NM AHEAD AND A CESSNA CITATION MAINT FACILITY WAS AT THE FIELD. CESSNA FOUND A 10 OHM LEAK TO GND ON THE SQUAT SWITCH AND ONE OUTFLOW VALVE THAT WAS LEAKING BEYOND SPECS. WE ALSO REPLACED THE PRESSURIZATION CTLR AS A PRECAUTION.

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.