Narrative:

At cruise, both pilots detected a sudden surge in cabin pressure via their ears. A visual check of pressure controller, cabin altitude, and cabin rate of climb showed a 1000+ FPM climb for 1-2 seconds, followed by a return to zero FPM. Cabin altitude was 7200 ft. A few seconds later, the surging started again with the rate of climb indicator pegging at plus or minus 4000 FPM. Captain switched the controller to 'standby,' which seemed to work for a few seconds, and then failed with cabin continuing to surge up and down. Captain switched controller to manual alternating current position with no effect. Outflow valve showed full closed, but cabin altitude climbed in excess of 10000 ft. Emergency descent was initiated with crew and passenger on oxygen (passenger masks deployed automatically). Leveled off at 10000 ft MSL. No explosive decompression occurred and aircraft flew normal throughout descent, approach, and landing. No structural, abnormal lights (door open), or flight control problems detected at 10000 ft MSL. Pressurization continued to surge with crew unable to control outflow valve, even with manual direct current selected on pressure controller, air condition/pressure packs turned off to prevent further surging and increase passenger comfort. Uneventful landing at denver international. No crew or passenger injuries. Callback conversation with reporter revealed the following information: reporter first officer had no definitive further information other than the pressurization controller was changed in the aircraft. He said that he had heard that the aircraft had another pressurization problem subsequent to their event, but knows nothing more. In their problem, they could not get control of the outflow valve in any position, either emergency alternating current or emergency direct current.

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Original NASA ASRS Text

Title: UNCTLABLE PRESSURIZATION. EMER DSCNT AND UNEVENTFUL LNDG. NO POST FLT INFO AVAILABLE.

Narrative: AT CRUISE, BOTH PLTS DETECTED A SUDDEN SURGE IN CABIN PRESSURE VIA THEIR EARS. A VISUAL CHK OF PRESSURE CTLR, CABIN ALT, AND CABIN RATE OF CLB SHOWED A 1000+ FPM CLB FOR 1-2 SECONDS, FOLLOWED BY A RETURN TO ZERO FPM. CABIN ALT WAS 7200 FT. A FEW SECONDS LATER, THE SURGING STARTED AGAIN WITH THE RATE OF CLB INDICATOR PEGGING AT PLUS OR MINUS 4000 FPM. CAPT SWITCHED THE CTLR TO 'STANDBY,' WHICH SEEMED TO WORK FOR A FEW SECONDS, AND THEN FAILED WITH CABIN CONTINUING TO SURGE UP AND DOWN. CAPT SWITCHED CTLR TO MANUAL ALTERNATING CURRENT POS WITH NO EFFECT. OUTFLOW VALVE SHOWED FULL CLOSED, BUT CABIN ALT CLBED IN EXCESS OF 10000 FT. EMER DSCNT WAS INITIATED WITH CREW AND PAX ON OXYGEN (PAX MASKS DEPLOYED AUTOMATICALLY). LEVELED OFF AT 10000 FT MSL. NO EXPLOSIVE DECOMPRESSION OCCURRED AND ACFT FLEW NORMAL THROUGHOUT DSCNT, APCH, AND LNDG. NO STRUCTURAL, ABNORMAL LIGHTS (DOOR OPEN), OR FLT CTL PROBS DETECTED AT 10000 FT MSL. PRESSURIZATION CONTINUED TO SURGE WITH CREW UNABLE TO CTL OUTFLOW VALVE, EVEN WITH MANUAL DIRECT CURRENT SELECTED ON PRESSURE CTLR, AIR CONDITION/PRESSURE PACKS TURNED OFF TO PREVENT FURTHER SURGING AND INCREASE PAX COMFORT. UNEVENTFUL LNDG AT DENVER INTL. NO CREW OR PAX INJURIES. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR FO HAD NO DEFINITIVE FURTHER INFO OTHER THAN THE PRESSURIZATION CTLR WAS CHANGED IN THE ACFT. HE SAID THAT HE HAD HEARD THAT THE ACFT HAD ANOTHER PRESSURIZATION PROB SUBSEQUENT TO THEIR EVENT, BUT KNOWS NOTHING MORE. IN THEIR PROB, THEY COULD NOT GET CTL OF THE OUTFLOW VALVE IN ANY POS, EITHER EMER ALTERNATING CURRENT OR EMER DIRECT CURRENT.

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.