Narrative:

West of prescott prc could see cumulus build-up and went off frequency to check on WX. Flight watch said the tops appeared to be above 30000 ft and suggested deviation to the north. Center approved. Flying at 11000 ft began encountering moderate rime and some clear ice. Requested lower from center but they couldn't approve at that time. Due to IFR conditions the center controllers were very busy. Northwest of prc the engine began to cut out and I began to lose altitude I immediately killed the autoplt, turned on the boost pump and switched tanks. This helped a little bit but I still could not retain altitude. I declared an emergency and never heard directly from center again. Fortunately, a citation above relayed center's vectors to the nearest airport (valle 40G). I broke out of the clouds approximately 700 ft AGL and began to regain power. Flew to airport and landed. In retrospect, it was not the ice that brought me down, but probably the fact that I had left my ram air open with ice and freezing rain blowing into the engine compartment. Callback conversation with reporter revealed the following information: the fuel injected mooney has a ram air system to increase manifold pressure at higher altitudes. It is recommended that it not be open in rain. On preflight the next day it was found to be open even though the reporter says he never uses it below 5000 ft. He assumes it was open at altitude and was left that way during descent and landing. Power was available below the icing conditions but was not normal throughout the approach and landing.

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Original NASA ASRS Text

Title: MOONEY PLT ENCOUNTERS ICE NEAR PRC, AZ. UNABLE TO MAINTAIN ALT DUE TO PWR LOSS, DECLARES EMER, DSNDS, COORDINATES WITH ARTCC THROUGH PASSING ACFT AND DIVERTS TO ANOTHER ARPT.

Narrative: W OF PRESCOTT PRC COULD SEE CUMULUS BUILD-UP AND WENT OFF FREQ TO CHK ON WX. FLT WATCH SAID THE TOPS APPEARED TO BE ABOVE 30000 FT AND SUGGESTED DEV TO THE N. CTR APPROVED. FLYING AT 11000 FT BEGAN ENCOUNTERING MODERATE RIME AND SOME CLR ICE. REQUESTED LOWER FROM CTR BUT THEY COULDN'T APPROVE AT THAT TIME. DUE TO IFR CONDITIONS THE CTR CTLRS WERE VERY BUSY. NW OF PRC THE ENG BEGAN TO CUT OUT AND I BEGAN TO LOSE ALT I IMMEDIATELY KILLED THE AUTOPLT, TURNED ON THE BOOST PUMP AND SWITCHED TANKS. THIS HELPED A LITTLE BIT BUT I STILL COULD NOT RETAIN ALT. I DECLARED AN EMER AND NEVER HEARD DIRECTLY FROM CTR AGAIN. FORTUNATELY, A CITATION ABOVE RELAYED CTR'S VECTORS TO THE NEAREST ARPT (VALLE 40G). I BROKE OUT OF THE CLOUDS APPROX 700 FT AGL AND BEGAN TO REGAIN PWR. FLEW TO ARPT AND LANDED. IN RETROSPECT, IT WAS NOT THE ICE THAT BROUGHT ME DOWN, BUT PROBABLY THE FACT THAT I HAD LEFT MY RAM AIR OPEN WITH ICE AND FREEZING RAIN BLOWING INTO THE ENG COMPARTMENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FUEL INJECTED MOONEY HAS A RAM AIR SYS TO INCREASE MANIFOLD PRESSURE AT HIGHER ALTS. IT IS RECOMMENDED THAT IT NOT BE OPEN IN RAIN. ON PREFLT THE NEXT DAY IT WAS FOUND TO BE OPEN EVEN THOUGH THE RPTR SAYS HE NEVER USES IT BELOW 5000 FT. HE ASSUMES IT WAS OPEN AT ALT AND WAS LEFT THAT WAY DURING DSCNT AND LNDG. PWR WAS AVAILABLE BELOW THE ICING CONDITIONS BUT WAS NOT NORMAL THROUGHOUT THE APCH AND LNDG.

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.