Narrative:

As we climbed to cruise altitude the automatic cabin pressure controller was slightly erratic. Soon after we leveled off at FL330 the cabin pressure began to fluctuate +/-1000 FPM for no apparent reason. We attempted to select manual pressurization control, but the cabin pressure began to rise rapidly, seemingly out of control. We could not initially control the cabin pressure and therefore felt the need for an immediate descent. We donned our oxygen masks and requested an immediate emergency descent to 10000 ft. As we descended we regained control of the pressure using the manual pressurization system. The cabin altitude increased high enough to automatically deploy the cabin oxygen masks. The cabin crew and passenger were told to use the masks. We verified we had properly accomplished the company's emergency procedures and we discontinued using oxygen as we leveled at 10000 ft. We directed the cabin to do the same. We checked for structural damage (found none) and checked for medical problems with the passenger (none we idented to the crew). All other system were normal. We requested no further emergency assistance, but elected to land short of our destination in little rock, ar. An uneventful landing was made in little rock airport. Callback conversation with reporter revealed the following information: callback revealed that the failure was in the automatic system. Cabin was controllable with manual, but the descent was not fast enough to prevent oxygen mask deployment so the diversion was made.

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Original NASA ASRS Text

Title: AN ACR DC9 HAS PRESSURIZATION CTL PROB, DECLARES EMER FOR DSCNT AND DIVERTS TO AN ENRTE ARPT.

Narrative: AS WE CLBED TO CRUISE ALT THE AUTOMATIC CABIN PRESSURE CTLR WAS SLIGHTLY ERRATIC. SOON AFTER WE LEVELED OFF AT FL330 THE CABIN PRESSURE BEGAN TO FLUCTUATE +/-1000 FPM FOR NO APPARENT REASON. WE ATTEMPTED TO SELECT MANUAL PRESSURIZATION CTL, BUT THE CABIN PRESSURE BEGAN TO RISE RAPIDLY, SEEMINGLY OUT OF CTL. WE COULD NOT INITIALLY CTL THE CABIN PRESSURE AND THEREFORE FELT THE NEED FOR AN IMMEDIATE DSCNT. WE DONNED OUR OXYGEN MASKS AND REQUESTED AN IMMEDIATE EMER DSCNT TO 10000 FT. AS WE DSNDED WE REGAINED CTL OF THE PRESSURE USING THE MANUAL PRESSURIZATION SYS. THE CABIN ALT INCREASED HIGH ENOUGH TO AUTOMATICALLY DEPLOY THE CABIN OXYGEN MASKS. THE CABIN CREW AND PAX WERE TOLD TO USE THE MASKS. WE VERIFIED WE HAD PROPERLY ACCOMPLISHED THE COMPANY'S EMER PROCS AND WE DISCONTINUED USING OXYGEN AS WE LEVELED AT 10000 FT. WE DIRECTED THE CABIN TO DO THE SAME. WE CHKED FOR STRUCTURAL DAMAGE (FOUND NONE) AND CHKED FOR MEDICAL PROBS WITH THE PAX (NONE WE IDENTED TO THE CREW). ALL OTHER SYS WERE NORMAL. WE REQUESTED NO FURTHER EMER ASSISTANCE, BUT ELECTED TO LAND SHORT OF OUR DEST IN LITTLE ROCK, AR. AN UNEVENTFUL LNDG WAS MADE IN LITTLE ROCK ARPT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CALLBACK REVEALED THAT THE FAILURE WAS IN THE AUTOMATIC SYS. CABIN WAS CONTROLLABLE WITH MANUAL, BUT THE DSCNT WAS NOT FAST ENOUGH TO PREVENT OXYGEN MASK DEPLOYMENT SO THE DIVERSION WAS MADE.

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.