Narrative:

We were climbing to FL230. At approximately FL200 we had the 'cabin alt/config' warning horn sound. We donned our O2 masks and proceeded with our memory items. The captain leveled off at FL210; called center; declared an emergency and asked for lower altitude and a turn to deviate around weather in the area. I ran the QRH procedures. The controller didn't seem to understand the nature of our emergency and tried to only clear us down to FL180 (there was a lot of traffic in the sector). We were then cleared down to 11;000 ft and given a turn direct [to departure airport]. The cabin altitude made it up to 13;000 ft and we were able to descend before it climbed any higher. The QRH has you go straight to manual AC or dc which I did and closed the outflow valve enough to start the cabin back down. In the middle of all this I sent a message to [operations] and advised them of the situation and that we had declared an emergency; the captain notified the flight attendant's what was going on and that we were returning to [departure airport]. We discussed what had happened and the fact that we never got an auto fail light and that maybe the standby mode would work. I switched it to standby and then the controller worked normally. We then briefed the approach and ran the overweight landing decent/approach check list. The approach was made through heavy weather (moderate turbulence and heavy rain). We weighed 124;000 pounds and did a flaps 30 landing. Touchdown was at approximately 100 FPM. The captain did an outstanding job!

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Original NASA ASRS Text

Title: A B737-400 flight crew reported loss of cabin pressure climbing through FL200. They declared an emergency and descended; regained control of the cabin when the procedure was run; and returned to departure airport.

Narrative: We were climbing to FL230. At approximately FL200 we had the 'cabin alt/config' warning horn sound. We donned our O2 masks and proceeded with our memory items. The Captain leveled off at FL210; called Center; declared an emergency and asked for lower altitude and a turn to deviate around weather in the area. I ran the QRH procedures. The Controller didn't seem to understand the nature of our emergency and tried to only clear us down to FL180 (there was a lot of traffic in the sector). We were then cleared down to 11;000 FT and given a turn direct [to departure airport]. The cabin altitude made it up to 13;000 FT and we were able to descend before it climbed any higher. The QRH has you go straight to manual AC or DC which I did and closed the outflow valve enough to start the cabin back down. In the middle of all this I sent a message to [operations] and advised them of the situation and that we had declared an emergency; the Captain notified the Flight Attendant's what was going on and that we were returning to [departure airport]. We discussed what had happened and the fact that we never got an auto fail light and that maybe the Standby mode would work. I switched it to Standby and then the controller worked normally. We then briefed the approach and ran the overweight landing Decent/Approach check list. The approach was made through heavy weather (moderate turbulence and heavy rain). We weighed 124;000 LBS and did a flaps 30 landing. Touchdown was at approximately 100 FPM. The Captain did an outstanding job!

Data retrieved from NASA's ASRS site as of April 2012 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.