Narrative:

The initial problem was a tail compartment high temperature light. Following emergency and abnormal procedure resulted in shutting down one pack. This solved the problem, but left us with a 1-PACK operation. The 1 pack could not maintain cabin altitude resulting in cabin altitude going above 10000'. This resulted in an emergency descent down to a habitual altitude, and a diversion to bwi. Oxygen masks were deployed and passenger advised to use them, which they did. Flight landed at bwi west/O further incident. When the emergency descent was initiated we did declare an emergency and squawked 7700'. Callback conversation with reporter revealed the following: a loose duct connection was the source of heat that triggered the high temperature light in the tail compartment. Reporter says it is not an uncommon occurrence on this aircraft when operating at high ambient temperature and that turning off the high pressure bleeds usually corrects the problem. On this occasion the flight crew had to turn off the packs alternately to isolate the problem and they did not notice the cabin pressurization loss until the warning horn sounded and the masks dropped. It was later determined that the remaining pack was not functioning at full output as expected and this allowed the cabin altitude in increase.

Related reports:

Google
 

Original NASA ASRS Text

Title: ACR MLG UNABLE TO MAINTAIN CABIN ALT ON ONE PACK MADE AN EMERGENCY DESCENT AND DIVERTED TO ALTERNATE.

Narrative: THE INITIAL PROB WAS A TAIL COMPARTMENT HIGH TEMP LIGHT. FOLLOWING EMER AND ABNORMAL PROC RESULTED IN SHUTTING DOWN ONE PACK. THIS SOLVED THE PROB, BUT LEFT US WITH A 1-PACK OPERATION. THE 1 PACK COULD NOT MAINTAIN CABIN ALT RESULTING IN CABIN ALT GOING ABOVE 10000'. THIS RESULTED IN AN EMER DSCNT DOWN TO A HABITUAL ALT, AND A DIVERSION TO BWI. OXYGEN MASKS WERE DEPLOYED AND PAX ADVISED TO USE THEM, WHICH THEY DID. FLT LANDED AT BWI W/O FURTHER INCIDENT. WHEN THE EMER DSCNT WAS INITIATED WE DID DECLARE AN EMER AND SQUAWKED 7700'. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: A LOOSE DUCT CONNECTION WAS THE SOURCE OF HEAT THAT TRIGGERED THE HIGH TEMP LIGHT IN THE TAIL COMPARTMENT. RPTR SAYS IT IS NOT AN UNCOMMON OCCURRENCE ON THIS ACFT WHEN OPERATING AT HIGH AMBIENT TEMP AND THAT TURNING OFF THE HIGH PRESSURE BLEEDS USUALLY CORRECTS THE PROB. ON THIS OCCASION THE FLT CREW HAD TO TURN OFF THE PACKS ALTERNATELY TO ISOLATE THE PROB AND THEY DID NOT NOTICE THE CABIN PRESSURIZATION LOSS UNTIL THE WARNING HORN SOUNDED AND THE MASKS DROPPED. IT WAS LATER DETERMINED THAT THE REMAINING PACK WAS NOT FUNCTIONING AT FULL OUTPUT AS EXPECTED AND THIS ALLOWED THE CABIN ALT IN INCREASE.

Data retrieved from NASA's ASRS site as of August 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.