Light transport crew had cabin depressurization in ZAU class a.

Attributes
ACN	478286
Time
Date	200007
Day	Sat
Local Time Of Day	1801 To 2400
Place
State Reference	IL
Altitude	msl single value : 31000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zau.artcc
Operator	common carrier : charter
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Operating Under FAR Part	Part 135
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : charter
Function	flight crew : first officer
Qualification	pilot : cfi pilot : atp pilot : multi engine
Experience	flight time last 90 days : 190 flight time total : 5100 flight time type : 100
ASRS Report	478286
Person 2
Affiliation	company : charter
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	other
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft

Narrative:

ZAU issued a descent from cruise altitude (FL310) to FL240. While performing the descent check and resetting the cabin pressurization, I bumped the cabin 'dump' valve. We immediately lost pressurization. The captain asked for me to get clearance to 10000 ft and we donned crew oxygen. Chicago delayed clearance so we squawked 7700 and declared an emergency. We promptly received clearance to 10000 ft. Once at 10000 ft and the situation under control, we continued to our destination, which was nearby. Landed normally and uneventfully. Contributing factors: dump switch located directly beneath adjuster knob. Dump switch is unguarded. Dump switch is safety wired ineffectively. Dump switch is of a loose non-detented type. Pressurization controls are poorly lighted. How to prevent: look and make certain your big fingers will not bump anything. Suggested to chief pilot to add a guard, detented switch, or better safety wire.

Original NASA ASRS Text

Title: LTT CREW HAD CABIN DEPRESSURIZATION IN ZAU CLASS A.

Narrative: ZAU ISSUED A DSCNT FROM CRUISE ALT (FL310) TO FL240. WHILE PERFORMING THE DSCNT CHK AND RESETTING THE CABIN PRESSURIZATION, I BUMPED THE CABIN 'DUMP' VALVE. WE IMMEDIATELY LOST PRESSURIZATION. THE CAPT ASKED FOR ME TO GET CLRNC TO 10000 FT AND WE DONNED CREW OXYGEN. CHICAGO DELAYED CLRNC SO WE SQUAWKED 7700 AND DECLARED AN EMER. WE PROMPTLY RECEIVED CLRNC TO 10000 FT. ONCE AT 10000 FT AND THE SIT UNDER CTL, WE CONTINUED TO OUR DEST, WHICH WAS NEARBY. LANDED NORMALLY AND UNEVENTFULLY. CONTRIBUTING FACTORS: DUMP SWITCH LOCATED DIRECTLY BENEATH ADJUSTER KNOB. DUMP SWITCH IS UNGUARDED. DUMP SWITCH IS SAFETY WIRED INEFFECTIVELY. DUMP SWITCH IS OF A LOOSE NON-DETENTED TYPE. PRESSURIZATION CTLS ARE POORLY LIGHTED. HOW TO PREVENT: LOOK AND MAKE CERTAIN YOUR BIG FINGERS WILL NOT BUMP ANYTHING. SUGGESTED TO CHIEF PLT TO ADD A GUARD, DETENTED SWITCH, OR BETTER SAFETY WIRE.

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.