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.