Narrative:

Aircraft was 1.5 hours into the flight at FL410. The cabin temperature was continuing to increase even at maximum cool. We had selected cowl anti-ice on prior to entering an area of clouds and thunderstorm activity. 8-10 mins later we got a cooling turbine hot light on the opp side we were having a problem with. Following the checklist we turned off the affected pack, opened the isolation valve and immediately started to lose pressurization at a rate exceeding 2000 FPM. We immediately donned oxygen masks and asked for lower altitude from ny commercial radio. They were unable to clear us lower than FL390. We declared an emergency to get a lower altitude and diverted to bermuda 45 mins away. On the ground in bermuda it was discovered that the air conditioning unit for the cabin had iced up and severely reduced the flow of air. The fact that cowl anti-ice was on and the low flow of air through the iced up unit caused the one remaining unit to overheat. Once we selected it off we had very little pressurization.

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Original NASA ASRS Text

Title: CPR MLG UNABLE TO MAINTAIN CABIN ALT HAD TO DIVERT TO AN ALTERNATE. THE LEFT PACK HAD ICED UP AND THE RIGHT PACK OVERHEATED TRYING TO COMPENSATE.

Narrative: ACFT WAS 1.5 HRS INTO THE FLT AT FL410. THE CABIN TEMP WAS CONTINUING TO INCREASE EVEN AT MAX COOL. WE HAD SELECTED COWL ANTI-ICE ON PRIOR TO ENTERING AN AREA OF CLOUDS AND TSTM ACTIVITY. 8-10 MINS LATER WE GOT A COOLING TURBINE HOT LIGHT ON THE OPP SIDE WE WERE HAVING A PROB WITH. FOLLOWING THE CHKLIST WE TURNED OFF THE AFFECTED PACK, OPENED THE ISOLATION VALVE AND IMMEDIATELY STARTED TO LOSE PRESSURIZATION AT A RATE EXCEEDING 2000 FPM. WE IMMEDIATELY DONNED OXYGEN MASKS AND ASKED FOR LOWER ALT FROM NY COMMERCIAL RADIO. THEY WERE UNABLE TO CLR US LOWER THAN FL390. WE DECLARED AN EMER TO GET A LOWER ALT AND DIVERTED TO BERMUDA 45 MINS AWAY. ON THE GND IN BERMUDA IT WAS DISCOVERED THAT THE AIR CONDITIONING UNIT FOR THE CABIN HAD ICED UP AND SEVERELY REDUCED THE FLOW OF AIR. THE FACT THAT COWL ANTI-ICE WAS ON AND THE LOW FLOW OF AIR THROUGH THE ICED UP UNIT CAUSED THE ONE REMAINING UNIT TO OVERHEAT. ONCE WE SELECTED IT OFF WE HAD VERY LITTLE PRESSURIZATION.

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.