B737-300 crew lost cabin pressurization and made an emergency descent in ZAU class a airspace.

Attributes
ACN	491710
Time
Date	200011
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zau.artcc
State Reference	IL
Altitude	msl single value : 37000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau.artcc artcc : egtt.artcc
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
ASRS Report	491710
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : cabin alt. warning other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance controller : provided flight assist flight crew : declared emergency other
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

I was PF mdw-mht. When after reaching cruise altitude, approximately 10-15 mins, we lost cabin pressurization. I would not categorize it as rapid, but maybe towards total loss in about 10-15 seconds. I heard a hissing noise, felt pressure change, and then altitude warning horn. The captain took over aircraft control and directed me to don oxygen mask and turned over aft control to me, and directed a descent (emergency). The captain declared emergency to ATC, which was acknowledged with clearance to any required altitude. PF elected 10000 ft. Captain continued emergency checklist (bold face) while I continued flying the descent profile. Captain made several calls to flight attendants and passenger to ascertain their welfare. Upon reaching 10000 ft, review of checklist was completed. Status reviewed of crew and passenger reconfirmed no injuries. We had no reason to believe the aircraft was damaged. We determined sufficient fuel on board to fly to mht. Captain discussed all above with dispatch and the decision was made to continue to mht. Callback conversation with reporter revealed the following information: reporter was unsure of what the problem was, but thought maintenance replaced the cabin outflow valve. He had no other information.

Original NASA ASRS Text

Title: B737-300 CREW LOST CABIN PRESSURIZATION AND MADE AN EMER DSCNT IN ZAU CLASS A AIRSPACE.

Narrative: I WAS PF MDW-MHT. WHEN AFTER REACHING CRUISE ALT, APPROX 10-15 MINS, WE LOST CABIN PRESSURIZATION. I WOULD NOT CATEGORIZE IT AS RAPID, BUT MAYBE TOWARDS TOTAL LOSS IN ABOUT 10-15 SECONDS. I HEARD A HISSING NOISE, FELT PRESSURE CHANGE, AND THEN ALT WARNING HORN. THE CAPT TOOK OVER ACFT CTL AND DIRECTED ME TO DON OXYGEN MASK AND TURNED OVER AFT CTL TO ME, AND DIRECTED A DSCNT (EMER). THE CAPT DECLARED EMER TO ATC, WHICH WAS ACKNOWLEDGED WITH CLRNC TO ANY REQUIRED ALT. PF ELECTED 10000 FT. CAPT CONTINUED EMER CHKLIST (BOLD FACE) WHILE I CONTINUED FLYING THE DSCNT PROFILE. CAPT MADE SEVERAL CALLS TO FLT ATTENDANTS AND PAX TO ASCERTAIN THEIR WELFARE. UPON REACHING 10000 FT, REVIEW OF CHKLIST WAS COMPLETED. STATUS REVIEWED OF CREW AND PAX RECONFIRMED NO INJURIES. WE HAD NO REASON TO BELIEVE THE ACFT WAS DAMAGED. WE DETERMINED SUFFICIENT FUEL ON BOARD TO FLY TO MHT. CAPT DISCUSSED ALL ABOVE WITH DISPATCH AND THE DECISION WAS MADE TO CONTINUE TO MHT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS UNSURE OF WHAT THE PROB WAS, BUT THOUGHT MAINT REPLACED THE CABIN OUTFLOW VALVE. HE HAD NO OTHER INFO.

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.