Narrative:

We departed at XA00 heading for XXX with 32 passenger; first officer was PF. Climbing through mid -20's; a flight attendant in rear cabin called to ask us to warm it up in the back. First officer observed right pack valve indicator pegged full hot; and left pack full cold. Getting no reaction from manipulating the controls in automatic mode; he switched both sides to manual and brought the left valve off full cold to add heat to the cabin supply duct. This had the desired effect; satisfying the flight attendants throughout our brief cruise at FL280 and subsequent climb to FL360 per flight plan. All was well for the next hour. We were cleared direct when we were again called by the flight attendant saying it was cold. First officer moved both temperature control valves (still in manual) from 11 O'clock position to 12 O'clock position to provide additional heat. Approximately 10 mins later we heard a decrease in cabin 'air noise' and noticed the 'flow' light illuminated on the overhead panel. Our cabin altitude; which had been close to 8000 ft to begin with; was now climbing; so I requested a descent from ATC. We suspected one or both packs had overtemped and shut down and we were unable to control the cabin. The flight attendant called and said it was very cold; and I told her we had a pressurization problem and were descending; that the oxygen masks might deploy; and that I'd make a PA shortly. As the cabin approached 10000 ft; I told ATC we needed an emergency descent to 10000 ft. The cabin altitude warning went off at this time so we donned our masks and first officer continued his emergency descent to 10000 ft MSL. The cabin altitude reached a maximum of 15000 ft as we were descending through 15000 ft MSL. I spoke briefly to the passenger during the descent; to tell them we were in no danger; but descending due to a pressurization problem. The cabin quickly descended to 10000 ft and I told the flight attendants they could breathe normally and asked how the folks were doing. She said all were fine; and I made a PA telling them a divert might be likely; but we were assessing the situation. While troubleshooting our problem with the QRH; I made several unsuccessful attempts to contact our dispatcher by #2 radio. Our ACARS screen said 'no communication;' so I did not take the time to type a message. I restored the pack operation per QRH instruction as ATC asked our intentions. Since our pressurization system was now functioning; and being uncomfortable heading toward 11000 ft mountains at 10000 ft; I requested a climb back to FL250. As we began our climb; ATC said our company was trying to contact us. I again tried them on the other radio and found the dispatcher waiting. He confirmed our masks had dropped in the cabin and said this dictated landing at the nearest suitable airport. Though behind us; he determined ZZZ2 was our closest option; and we turned back for an uneventful landing there. 2 lessons learned: though light passenger loads and high cruise altitudes can make cabin heating a challenge; manual operation of the packs can be risky; especially anything more than momentary operation of a single side. So our attempts to provide heat in a non normal mode of operation may have caused us to be scooting low over terrain at night. My biggest mistake; in retrospect; was climbing back toward FL250 with spent oxygen generators in the occupied seats; no matter the fact that many were unused. I wish now that I had remained at 10000 ft; but whether it was the low altitude or a 'blind spot;' I was unable to confer with my dispatcher; and in the heat of the moment elected to climb to remove the first threat that came to mind -- the mountains I knew lay ahead. Though the climb allowed me to establish contact with the dispatcher; it is of little consolation. If the masks have dropped; there is no option but to stay at 10000 ft or MEA and find a place to land.

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Original NASA ASRS Text

Title: MD88 FLT CREW HAS LOSS OF PRESSURIZATION AT FL360; CABIN ALT WARNING ALERTS; EMER DSCNT REQUESTED; FLT CREW DIVERTS TO ANOTHER ARPT.

Narrative: WE DEPARTED AT XA00 HEADING FOR XXX WITH 32 PAX; FO WAS PF. CLBING THROUGH MID -20'S; A FLT ATTENDANT IN REAR CABIN CALLED TO ASK US TO WARM IT UP IN THE BACK. FO OBSERVED R PACK VALVE INDICATOR PEGGED FULL HOT; AND L PACK FULL COLD. GETTING NO REACTION FROM MANIPULATING THE CTLS IN AUTOMATIC MODE; HE SWITCHED BOTH SIDES TO MANUAL AND BROUGHT THE L VALVE OFF FULL COLD TO ADD HEAT TO THE CABIN SUPPLY DUCT. THIS HAD THE DESIRED EFFECT; SATISFYING THE FLT ATTENDANTS THROUGHOUT OUR BRIEF CRUISE AT FL280 AND SUBSEQUENT CLB TO FL360 PER FLT PLAN. ALL WAS WELL FOR THE NEXT HR. WE WERE CLRED DIRECT WHEN WE WERE AGAIN CALLED BY THE FLT ATTENDANT SAYING IT WAS COLD. FO MOVED BOTH TEMP CTL VALVES (STILL IN MANUAL) FROM 11 O'CLOCK POS TO 12 O'CLOCK POS TO PROVIDE ADDITIONAL HEAT. APPROX 10 MINS LATER WE HEARD A DECREASE IN CABIN 'AIR NOISE' AND NOTICED THE 'FLOW' LIGHT ILLUMINATED ON THE OVERHEAD PANEL. OUR CABIN ALT; WHICH HAD BEEN CLOSE TO 8000 FT TO BEGIN WITH; WAS NOW CLBING; SO I REQUESTED A DSCNT FROM ATC. WE SUSPECTED ONE OR BOTH PACKS HAD OVERTEMPED AND SHUT DOWN AND WE WERE UNABLE TO CTL THE CABIN. THE FLT ATTENDANT CALLED AND SAID IT WAS VERY COLD; AND I TOLD HER WE HAD A PRESSURIZATION PROB AND WERE DSNDING; THAT THE OXYGEN MASKS MIGHT DEPLOY; AND THAT I'D MAKE A PA SHORTLY. AS THE CABIN APCHED 10000 FT; I TOLD ATC WE NEEDED AN EMER DSCNT TO 10000 FT. THE CABIN ALT WARNING WENT OFF AT THIS TIME SO WE DONNED OUR MASKS AND FO CONTINUED HIS EMER DSCNT TO 10000 FT MSL. THE CABIN ALT REACHED A MAX OF 15000 FT AS WE WERE DSNDING THROUGH 15000 FT MSL. I SPOKE BRIEFLY TO THE PAX DURING THE DSCNT; TO TELL THEM WE WERE IN NO DANGER; BUT DSNDING DUE TO A PRESSURIZATION PROB. THE CABIN QUICKLY DSNDED TO 10000 FT AND I TOLD THE FLT ATTENDANTS THEY COULD BREATHE NORMALLY AND ASKED HOW THE FOLKS WERE DOING. SHE SAID ALL WERE FINE; AND I MADE A PA TELLING THEM A DIVERT MIGHT BE LIKELY; BUT WE WERE ASSESSING THE SITUATION. WHILE TROUBLESHOOTING OUR PROB WITH THE QRH; I MADE SEVERAL UNSUCCESSFUL ATTEMPTS TO CONTACT OUR DISPATCHER BY #2 RADIO. OUR ACARS SCREEN SAID 'NO COM;' SO I DID NOT TAKE THE TIME TO TYPE A MESSAGE. I RESTORED THE PACK OP PER QRH INSTRUCTION AS ATC ASKED OUR INTENTIONS. SINCE OUR PRESSURIZATION SYS WAS NOW FUNCTIONING; AND BEING UNCOMFORTABLE HEADING TOWARD 11000 FT MOUNTAINS AT 10000 FT; I REQUESTED A CLB BACK TO FL250. AS WE BEGAN OUR CLB; ATC SAID OUR COMPANY WAS TRYING TO CONTACT US. I AGAIN TRIED THEM ON THE OTHER RADIO AND FOUND THE DISPATCHER WAITING. HE CONFIRMED OUR MASKS HAD DROPPED IN THE CABIN AND SAID THIS DICTATED LNDG AT THE NEAREST SUITABLE ARPT. THOUGH BEHIND US; HE DETERMINED ZZZ2 WAS OUR CLOSEST OPTION; AND WE TURNED BACK FOR AN UNEVENTFUL LNDG THERE. 2 LESSONS LEARNED: THOUGH LIGHT PAX LOADS AND HIGH CRUISE ALTS CAN MAKE CABIN HEATING A CHALLENGE; MANUAL OP OF THE PACKS CAN BE RISKY; ESPECIALLY ANYTHING MORE THAN MOMENTARY OP OF A SINGLE SIDE. SO OUR ATTEMPTS TO PROVIDE HEAT IN A NON NORMAL MODE OF OP MAY HAVE CAUSED US TO BE SCOOTING LOW OVER TERRAIN AT NIGHT. MY BIGGEST MISTAKE; IN RETROSPECT; WAS CLBING BACK TOWARD FL250 WITH SPENT OXYGEN GENERATORS IN THE OCCUPIED SEATS; NO MATTER THE FACT THAT MANY WERE UNUSED. I WISH NOW THAT I HAD REMAINED AT 10000 FT; BUT WHETHER IT WAS THE LOW ALT OR A 'BLIND SPOT;' I WAS UNABLE TO CONFER WITH MY DISPATCHER; AND IN THE HEAT OF THE MOMENT ELECTED TO CLB TO REMOVE THE FIRST THREAT THAT CAME TO MIND -- THE MOUNTAINS I KNEW LAY AHEAD. THOUGH THE CLB ALLOWED ME TO ESTABLISH CONTACT WITH THE DISPATCHER; IT IS OF LITTLE CONSOLATION. IF THE MASKS HAVE DROPPED; THERE IS NO OPTION BUT TO STAY AT 10000 FT OR MEA AND FIND A PLACE TO LAND.

Data retrieved from NASA's ASRS site as of January 2009 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.