Narrative:

Flight atl-tul-dfw experienced pressurization problems while en route to tul. We were in level flight at FL310 when the cabin pressurization horn went off. The cabin altitude was at 10000' and climbing. The first officer switched to standby to try and control the cabin. When we realized we couldn't control the cabin, I told the first officer to declare an emergency and get me 10000'. I didn't understand what altitude the controller said and started to ask the first officer when he put 15000' in the altitude window. I then started my emergency descent. I then asked him to try and get me 10000'. About 20 seconds passed and 10000' was put in the altitude window. I returned to atl and made a normal landing. After we got on the ground my first officer said that we were only cleared to FL240. He spun the altitude down to get me started. I am not sure how close to FL240 I was before I was cleared to 10000'. Nothing was said about any altitude, so I am assuming that I was still above FL240 when I received clearance to 10000'. The first officer was trying to run the descent checklist and didn't realize he had put 15000' instead FL240. Callback conversation with reporter revealed the following: a burned out control motor on the outflow valve caused the flight crew to lose control of cabin pressurization. The O2 masks did not come out and there were no injuries to passenger as a result of the emergency descent.

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Original NASA ASRS Text

Title: ACR MLG MADE AN EMERGENCY DESCENT WHEN FLT CREW WAS UNABLE TO CONTROL CABIN PRESSURIZATION.

Narrative: FLT ATL-TUL-DFW EXPERIENCED PRESSURIZATION PROBS WHILE ENRTE TO TUL. WE WERE IN LEVEL FLT AT FL310 WHEN THE CABIN PRESSURIZATION HORN WENT OFF. THE CABIN ALT WAS AT 10000' AND CLBING. THE F/O SWITCHED TO STANDBY TO TRY AND CTL THE CABIN. WHEN WE REALIZED WE COULDN'T CTL THE CABIN, I TOLD THE F/O TO DECLARE AN EMER AND GET ME 10000'. I DIDN'T UNDERSTAND WHAT ALT THE CTLR SAID AND STARTED TO ASK THE F/O WHEN HE PUT 15000' IN THE ALT WINDOW. I THEN STARTED MY EMER DSCNT. I THEN ASKED HIM TO TRY AND GET ME 10000'. ABOUT 20 SECS PASSED AND 10000' WAS PUT IN THE ALT WINDOW. I RETURNED TO ATL AND MADE A NORMAL LNDG. AFTER WE GOT ON THE GND MY F/O SAID THAT WE WERE ONLY CLRED TO FL240. HE SPUN THE ALT DOWN TO GET ME STARTED. I AM NOT SURE HOW CLOSE TO FL240 I WAS BEFORE I WAS CLRED TO 10000'. NOTHING WAS SAID ABOUT ANY ALT, SO I AM ASSUMING THAT I WAS STILL ABOVE FL240 WHEN I RECEIVED CLRNC TO 10000'. THE F/O WAS TRYING TO RUN THE DSCNT CHKLIST AND DIDN'T REALIZE HE HAD PUT 15000' INSTEAD FL240. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: A BURNED OUT CTL MOTOR ON THE OUTFLOW VALVE CAUSED THE FLT CREW TO LOSE CTL OF CABIN PRESSURIZATION. THE O2 MASKS DID NOT COME OUT AND THERE WERE NO INJURIES TO PAX AS A RESULT OF THE EMER DSCNT.

Data retrieved from NASA's ASRS site as of August 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.