Narrative:

A large storm system was on the radar and had been reported from just east of ama, reaching northeast to about ict. Tops to 5500 ft. We were in the clear, but as we approached within 30 NM north of the western most storms, we turned 30 degrees right 240-250 degree heading in order to stay north and west of the WX. At this point, we entered clouds, started picking up light to moderate chop and turbulence. After 10-15 mins, we noticed ice beginning to build up and getting worse. I turned an additional 20 degrees right in hopes that we would more rapidly exit the WX. 5-10 mins later, just north of ama, we did exit into clear air and deiced the tail for a second time to clean off remaining structural ice. Within 5 mins of this, our attention was drawn to the annunciator panel by an amber pressurization flow light. The cabin pressure was increasing by 600-70 ft and the cabin was already above 9000 ft and rising. Pressure on l-hand pack was 27 psi, r-hand pack was 25 psi. Initial reaction was to adjust temperature higher in hopes of adding more air and perhaps unfreezing potentially frozen valves. This did not solve the problem, so we requested and received clearance to descend to FL250. We also immediately proceeded with rapid decompression checklist. Manually closing the outflow valve did not immediately arrest the cabin's climb. As we descended, the cabin hit 10000 ft and the red cabin pressure light came on. At this point, I declared emergency and received clearance to 10000 ft. We completed explosive decompression checklist. I elected not to have the first officer eject the passenger oxygen masks because I needed him to help me complete other duties with the aircraft and we were having some problems with the intercockpit communication. The passenger masks never dropped, probably because at some point before 10000 ft, the outflow valve drove full closed and the cabin repressurized. In fact, that was my lesson learned. We were so busy with the aircraft control and communication that the cabin pressure drove to zero by the time we leveled at 10000 ft and we noticed it. We re-established autopressure control and that worked into elp. 2 passenger received medical attention at the gate for blocked sinus and ears. The passenger were ok after EMS attended to them.

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Original NASA ASRS Text

Title: MD80 CREW LOST CTL OF CABIN PRESSURIZATION AND WAS REQUIRED TO MAKE AN EMER DSCNT TO 10000 FT.

Narrative: A LARGE STORM SYS WAS ON THE RADAR AND HAD BEEN RPTED FROM JUST E OF AMA, REACHING NE TO ABOUT ICT. TOPS TO 5500 FT. WE WERE IN THE CLR, BUT AS WE APCHED WITHIN 30 NM N OF THE WESTERN MOST STORMS, WE TURNED 30 DEGS R 240-250 DEG HDG IN ORDER TO STAY N AND W OF THE WX. AT THIS POINT, WE ENTERED CLOUDS, STARTED PICKING UP LIGHT TO MODERATE CHOP AND TURB. AFTER 10-15 MINS, WE NOTICED ICE BEGINNING TO BUILD UP AND GETTING WORSE. I TURNED AN ADDITIONAL 20 DEGS R IN HOPES THAT WE WOULD MORE RAPIDLY EXIT THE WX. 5-10 MINS LATER, JUST N OF AMA, WE DID EXIT INTO CLR AIR AND DEICED THE TAIL FOR A SECOND TIME TO CLEAN OFF REMAINING STRUCTURAL ICE. WITHIN 5 MINS OF THIS, OUR ATTN WAS DRAWN TO THE ANNUNCIATOR PANEL BY AN AMBER PRESSURIZATION FLOW LIGHT. THE CABIN PRESSURE WAS INCREASING BY 600-70 FT AND THE CABIN WAS ALREADY ABOVE 9000 FT AND RISING. PRESSURE ON L-HAND PACK WAS 27 PSI, R-HAND PACK WAS 25 PSI. INITIAL REACTION WAS TO ADJUST TEMP HIGHER IN HOPES OF ADDING MORE AIR AND PERHAPS UNFREEZING POTENTIALLY FROZEN VALVES. THIS DID NOT SOLVE THE PROB, SO WE REQUESTED AND RECEIVED CLRNC TO DSND TO FL250. WE ALSO IMMEDIATELY PROCEEDED WITH RAPID DECOMPRESSION CHKLIST. MANUALLY CLOSING THE OUTFLOW VALVE DID NOT IMMEDIATELY ARREST THE CABIN'S CLB. AS WE DSNDED, THE CABIN HIT 10000 FT AND THE RED CABIN PRESSURE LIGHT CAME ON. AT THIS POINT, I DECLARED EMER AND RECEIVED CLRNC TO 10000 FT. WE COMPLETED EXPLOSIVE DECOMPRESSION CHKLIST. I ELECTED NOT TO HAVE THE FO EJECT THE PAX OXYGEN MASKS BECAUSE I NEEDED HIM TO HELP ME COMPLETE OTHER DUTIES WITH THE ACFT AND WE WERE HAVING SOME PROBS WITH THE INTERCOCKPIT COM. THE PAX MASKS NEVER DROPPED, PROBABLY BECAUSE AT SOME POINT BEFORE 10000 FT, THE OUTFLOW VALVE DROVE FULL CLOSED AND THE CABIN REPRESSURIZED. IN FACT, THAT WAS MY LESSON LEARNED. WE WERE SO BUSY WITH THE ACFT CTL AND COM THAT THE CABIN PRESSURE DROVE TO ZERO BY THE TIME WE LEVELED AT 10000 FT AND WE NOTICED IT. WE RE-ESTABLISHED AUTOPRESSURE CTL AND THAT WORKED INTO ELP. 2 PAX RECEIVED MEDICAL ATTN AT THE GATE FOR BLOCKED SINUS AND EARS. THE PAX WERE OK AFTER EMS ATTENDED TO THEM.

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.