Light transport air taxi has pressurization problem at cruise. Unable to contact ATC makes emergency...

Attributes
ACN	323490
Time
Date	199512
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : yyj
State Reference	BC
Altitude	msl bound lower : 35000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zse
Operator	common carrier : air taxi
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 135
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 30 flight time total : 5300 flight time type : 1600
ASRS Report	323490
Person 2
Affiliation	company : air carrier
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 : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

While at cruise FL350 we heard a muffled 'pop' followed by a change in cabin pressure, cabin climbing at 6000 FPM. I commanded the PNF to manually control the cabin rate. He replied that he was unable to manually control it by the manufacturer's procedures so we donned our oxygen masks, dropped masks to passenger and attempted to advise ATC of request for immediate descent. Received no response from ATC so I initiated a rapid descent straight ahead. We declared an emergency due to loss of cabin pressure and this time ATC received that part of our transmission and cleared us to do whatever we needed. We continued descent to 9000 ft MSL and received vectors back to our home base (bfi). The emergency pressurization system automatically activated and was able to maintain some pressurization. We continued in and landed without incident. Maintenance discovered that a duct had come loose in the cabin pressurization bleed air system.

Original NASA ASRS Text

Title: LTT AIR TAXI HAS PRESSURIZATION PROB AT CRUISE. UNABLE TO CONTACT ATC MAKES EMER DSCNT.

Narrative: WHILE AT CRUISE FL350 WE HEARD A MUFFLED 'POP' FOLLOWED BY A CHANGE IN CABIN PRESSURE, CABIN CLBING AT 6000 FPM. I COMMANDED THE PNF TO MANUALLY CTL THE CABIN RATE. HE REPLIED THAT HE WAS UNABLE TO MANUALLY CTL IT BY THE MANUFACTURER'S PROCS SO WE DONNED OUR OXYGEN MASKS, DROPPED MASKS TO PAX AND ATTEMPTED TO ADVISE ATC OF REQUEST FOR IMMEDIATE DSCNT. RECEIVED NO RESPONSE FROM ATC SO I INITIATED A RAPID DSCNT STRAIGHT AHEAD. WE DECLARED AN EMER DUE TO LOSS OF CABIN PRESSURE AND THIS TIME ATC RECEIVED THAT PART OF OUR XMISSION AND CLRED US TO DO WHATEVER WE NEEDED. WE CONTINUED DSCNT TO 9000 FT MSL AND RECEIVED VECTORS BACK TO OUR HOME BASE (BFI). THE EMER PRESSURIZATION SYS AUTOMATICALLY ACTIVATED AND WAS ABLE TO MAINTAIN SOME PRESSURIZATION. WE CONTINUED IN AND LANDED WITHOUT INCIDENT. MAINT DISCOVERED THAT A DUCT HAD COME LOOSE IN THE CABIN PRESSURIZATION BLEED AIR SYS.

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.

Light transport air taxi has pressurization problem at cruise. Unable to contact ATC makes emergency descent.