Narrative:

While flying at FL290 in instrument WX conditions, with the ice protection system on, we observed the cabin altitude climbing 1000 FPM. The left and right packs were on automatic with a pressure reading of 12 psi. The left duct was colder than the right, but each was within limits. With the outflow valve fully closed and the cabin continuing to climb, we donned the oxygen mask. The first officer continued to fly the aircraft, while talking with ATC. I opened the cabin door and told the lead flight attendant to 'situation down and put on an oxygen mask.' the communication procedures of 'cabin pressure loss' and 'rapid descent' were completed. As we were passing FL200 the red cabin pressure annunciator light and master caution light illuminated. Passing 15000 ft, the cabin started to pressurize. With the cabin pressurizing, I elected not to deploy the passenger oxygen mask. An emergency was declared with ZTL. I also tried to contact dispatch on the company radio, but was unsuccessful. Being unable to contact dispatch on the radio, a message was sent via ACARS. Dispatch notified knoxville operations that we were en route. The passenger were informed of our pressurization problem and that we were diverting into knoxville. The WX at tys was 400 ft broken, with light rain and mist with 2 mi visibility. A normal landing was made at tys. After parking, the passenger were informed of the problem and were deplaned into the terminal. Maintenance control, dispatch, and a chief pilot were called. Each flight attendant was debriefed to determine their emotional condition, and asked if they would be willing to continue. After a local mechanic MEL'ed the pressurization system, the aircraft was flown with passenger to rdu. The arrival time at rdu was 3 mins past the far scheduled duty period.

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Original NASA ASRS Text

Title: A DC9 FLT CREW EXPERIENCE A LOSS OF CABIN PRESSURE RESULTING IN AN EMER DSCNT AND LNG.

Narrative: WHILE FLYING AT FL290 IN INST WX CONDITIONS, WITH THE ICE PROTECTION SYS ON, WE OBSERVED THE CABIN ALT CLBING 1000 FPM. THE L AND R PACKS WERE ON AUTO WITH A PRESSURE READING OF 12 PSI. THE L DUCT WAS COLDER THAN THE R, BUT EACH WAS WITHIN LIMITS. WITH THE OUTFLOW VALVE FULLY CLOSED AND THE CABIN CONTINUING TO CLB, WE DONNED THE OXYGEN MASK. THE FO CONTINUED TO FLY THE ACFT, WHILE TALKING WITH ATC. I OPENED THE CABIN DOOR AND TOLD THE LEAD FLT ATTENDANT TO 'SIT DOWN AND PUT ON AN OXYGEN MASK.' THE COM PROCS OF 'CABIN PRESSURE LOSS' AND 'RAPID DSCNT' WERE COMPLETED. AS WE WERE PASSING FL200 THE RED CABIN PRESSURE ANNUNCIATOR LIGHT AND MASTER CAUTION LIGHT ILLUMINATED. PASSING 15000 FT, THE CABIN STARTED TO PRESSURIZE. WITH THE CABIN PRESSURIZING, I ELECTED NOT TO DEPLOY THE PAX OXYGEN MASK. AN EMER WAS DECLARED WITH ZTL. I ALSO TRIED TO CONTACT DISPATCH ON THE COMPANY RADIO, BUT WAS UNSUCCESSFUL. BEING UNABLE TO CONTACT DISPATCH ON THE RADIO, A MESSAGE WAS SENT VIA ACARS. DISPATCH NOTIFIED KNOXVILLE OPS THAT WE WERE ENRTE. THE PAX WERE INFORMED OF OUR PRESSURIZATION PROB AND THAT WE WERE DIVERTING INTO KNOXVILLE. THE WX AT TYS WAS 400 FT BROKEN, WITH LIGHT RAIN AND MIST WITH 2 MI VISIBILITY. A NORMAL LNDG WAS MADE AT TYS. AFTER PARKING, THE PAX WERE INFORMED OF THE PROB AND WERE DEPLANED INTO THE TERMINAL. MAINT CTL, DISPATCH, AND A CHIEF PLT WERE CALLED. EACH FLT ATTENDANT WAS DEBRIEFED TO DETERMINE THEIR EMOTIONAL CONDITION, AND ASKED IF THEY WOULD BE WILLING TO CONTINUE. AFTER A LCL MECH MEL'ED THE PRESSURIZATION SYS, THE ACFT WAS FLOWN WITH PAX TO RDU. THE ARR TIME AT RDU WAS 3 MINS PAST THE FAR SCHEDULED DUTY PERIOD.

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.