Narrative:

Flying at FL330 and on J165, 100 mi south of flat rock, we experienced a rise in cabin pressure. We performed the checklist for a flow control light and were unable to prevent the cabin from climbing at 500 FPM to 1000 FPM. We asked for a lower altitude and received FL310. We again asked for lower and received FL240. At FL240 the cabin continued climbing. Both pilots went on O2 masks as the cabin passed 9000'. We told center we were still experiencing cabin pressure problems and asked for a lower altitude. When the cabin reached 10000' and we could not stop the rise in cabin pressure, I declared an emergency and asked for 10000'. Center confirmed our flight with the emergency and initially gave us 16000'. After accomplishing emergency checklists, the cabin altitude exceeded 14000' and we deployed cabin O2 masks. Center now cleared us to 10000' and direct flat rock. Once at 10000' we requested vectors for a landing at rdu. We received our clearance and proceeded to rdu. Our cabin stabilized at 1000' and the F/a's were advised. They reported everyone was ok and requested no further assistance at rdu. Our approach and landing at rdu were normal. Maintenance at rdu reported the left pack ducting had separated and that it was impossible to control pressure with it separated. No altitudes were missed on flight routing in our emergency. Supplemental information from acn 159471: such a slow pressurization loss may at first appear less serious, but any delay in descending may lead to hypoxia for passenger and crew in cabin of O2 masks are not deployed.

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Original NASA ASRS Text

Title: ACR MLG LOST CABIN PRESSURIZATION CTL AT FL330. DIVERTED TO ALTERNATE.

Narrative: FLYING AT FL330 AND ON J165, 100 MI S OF FLAT ROCK, WE EXPERIENCED A RISE IN CABIN PRESSURE. WE PERFORMED THE CHKLIST FOR A FLOW CTL LIGHT AND WERE UNABLE TO PREVENT THE CABIN FROM CLBING AT 500 FPM TO 1000 FPM. WE ASKED FOR A LOWER ALT AND RECEIVED FL310. WE AGAIN ASKED FOR LOWER AND RECEIVED FL240. AT FL240 THE CABIN CONTINUED CLBING. BOTH PLTS WENT ON O2 MASKS AS THE CABIN PASSED 9000'. WE TOLD CENTER WE WERE STILL EXPERIENCING CABIN PRESSURE PROBS AND ASKED FOR A LOWER ALT. WHEN THE CABIN REACHED 10000' AND WE COULD NOT STOP THE RISE IN CABIN PRESSURE, I DECLARED AN EMER AND ASKED FOR 10000'. CENTER CONFIRMED OUR FLT WITH THE EMER AND INITIALLY GAVE US 16000'. AFTER ACCOMPLISHING EMER CHKLISTS, THE CABIN ALT EXCEEDED 14000' AND WE DEPLOYED CABIN O2 MASKS. CENTER NOW CLRED US TO 10000' AND DIRECT FLAT ROCK. ONCE AT 10000' WE REQUESTED VECTORS FOR A LNDG AT RDU. WE RECEIVED OUR CLRNC AND PROCEEDED TO RDU. OUR CABIN STABILIZED AT 1000' AND THE F/A'S WERE ADVISED. THEY RPTED EVERYONE WAS OK AND REQUESTED NO FURTHER ASSISTANCE AT RDU. OUR APCH AND LNDG AT RDU WERE NORMAL. MAINT AT RDU RPTED THE LEFT PACK DUCTING HAD SEPARATED AND THAT IT WAS IMPOSSIBLE TO CTL PRESSURE WITH IT SEPARATED. NO ALTS WERE MISSED ON FLT RTING IN OUR EMER. SUPPLEMENTAL INFO FROM ACN 159471: SUCH A SLOW PRESSURIZATION LOSS MAY AT FIRST APPEAR LESS SERIOUS, BUT ANY DELAY IN DSNDING MAY LEAD TO HYPOXIA FOR PAX AND CREW IN CABIN OF O2 MASKS ARE NOT DEPLOYED.

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.