Narrative:

Cruising 16000 ft in IMC, encountered unexpected thunderstorms with rapid ice (rime) accumulation. Requested and received deviation and block airspace 14000-16000 ft. Broke out at 14000 ft and the ice cleared. Received new vectors to rno direct. After 5 min in a new IMC layer, rapidly accumulated 2 inches mixed ice and, while attempting course reversal, engine lost power, continued running erratically and did not respond to fuel tank switch-over, auxiliary fuel pump activation or variation in mixture or propeller control. Problem may have been malfunction or freezing of alternate air door spring, or heavy propeller icing. With turbulence, and erratic engine, I declared emergency requesting vectors to nearest airport. Received clearance to yerington and descent to 9000 ft. Upon arrival at yerington, I was IMC at 9000 ft and requested further instructions. While waiting, engine performance became smooth and ctlable once again, totally normal! I was vectored to rno for the localizer back course 34 approach. By this time, the LORAN was disabled by WX, the DME was nominal, #1 VOR head was shorting out, flickering on and off and neither VOR head was detecting fmg VORTAC or rno ILS (110.9). Communication radio communication had become staticy as well. Notified approach that I thought I had passed the back course without interception due to the radio problem, received vectors and descent below the clouds and completed visual approach and landing. Am writing because I don't know what I did that may be wrong, but had to call ZOA upon landing because I declared an emergency. Note: I checked WX before departing phx on crossing over las at 14000 ft and again twice before and during IMC entry and passage. Only information was thunderstorm north of rno and light rime at 16000 ft intermittent south of rno. Also probably busted altitude and vectors in the turbulence encountered while engine was malfunctioning.

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Original NASA ASRS Text

Title: PVT INST RATED PLT ENCOUNTERS TSTM ACTIVITY AND NUMEROUS ACFT EQUIP PROBS. EMER DECLARED.

Narrative: CRUISING 16000 FT IN IMC, ENCOUNTERED UNEXPECTED TSTMS WITH RAPID ICE (RIME) ACCUMULATION. REQUESTED AND RECEIVED DEV AND BLOCK AIRSPACE 14000-16000 FT. BROKE OUT AT 14000 FT AND THE ICE CLEARED. RECEIVED NEW VECTORS TO RNO DIRECT. AFTER 5 MIN IN A NEW IMC LAYER, RAPIDLY ACCUMULATED 2 INCHES MIXED ICE AND, WHILE ATTEMPTING COURSE REVERSAL, ENG LOST PWR, CONTINUED RUNNING ERRATICALLY AND DID NOT RESPOND TO FUEL TANK SWITCH-OVER, AUX FUEL PUMP ACTIVATION OR VARIATION IN MIXTURE OR PROP CTL. PROB MAY HAVE BEEN MALFUNCTION OR FREEZING OF ALTERNATE AIR DOOR SPRING, OR HVY PROP ICING. WITH TURB, AND ERRATIC ENG, I DECLARED EMER REQUESTING VECTORS TO NEAREST ARPT. RECEIVED CLRNC TO YERINGTON AND DSCNT TO 9000 FT. UPON ARR AT YERINGTON, I WAS IMC AT 9000 FT AND REQUESTED FURTHER INSTRUCTIONS. WHILE WAITING, ENG PERFORMANCE BECAME SMOOTH AND CTLABLE ONCE AGAIN, TOTALLY NORMAL! I WAS VECTORED TO RNO FOR THE LOC BACK COURSE 34 APCH. BY THIS TIME, THE LORAN WAS DISABLED BY WX, THE DME WAS NOMINAL, #1 VOR HEAD WAS SHORTING OUT, FLICKERING ON AND OFF AND NEITHER VOR HEAD WAS DETECTING FMG VORTAC OR RNO ILS (110.9). COM RADIO COM HAD BECOME STATICY AS WELL. NOTIFIED APCH THAT I THOUGHT I HAD PASSED THE BACK COURSE WITHOUT INTERCEPTION DUE TO THE RADIO PROB, RECEIVED VECTORS AND DSCNT BELOW THE CLOUDS AND COMPLETED VISUAL APCH AND LNDG. AM WRITING BECAUSE I DON'T KNOW WHAT I DID THAT MAY BE WRONG, BUT HAD TO CALL ZOA UPON LNDG BECAUSE I DECLARED AN EMER. NOTE: I CHKED WX BEFORE DEPARTING PHX ON XING OVER LAS AT 14000 FT AND AGAIN TWICE BEFORE AND DURING IMC ENTRY AND PASSAGE. ONLY INFO WAS TSTM N OF RNO AND LIGHT RIME AT 16000 FT INTERMITTENT S OF RNO. ALSO PROBABLY BUSTED ALT AND VECTORS IN THE TURB ENCOUNTERED WHILE ENG WAS MALFUNCTIONING.

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.