PVT PLT OF A C340 ACFT LEFT ASSIGNED ALT DUE TO INFLT ENCOUNTER WITH ICING WX CONDITIONS AND HAD COMPLETE PRIMARY ELECTRICAL SUPPLY PROB.

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UPON INITIAL CLB OUT OF SUN VALLEY IN LIGHT SNOW ON AN IFR FLT PLAN; ENG BEGAN RUNNING VERY ROUGH; MISSING AND SPUTTERING. BECAUSE OF WX AND TERRAIN; RETURN TO KSUN WAS NOT DEEMED FEASIBLE SO PLT CONTINUED CLB TO ASSIGNED ALT OF 9000 FT MSL ENRTE TO DEST/NEAREST ARPT; TWIN FALLS. UPON REACHING ASSIGNED ALT; ENGS WERE RUNNING SMOOTHLY AND WITHIN NORMAL OPERATING LIMITS. SHORTLY AFTER MAKING CONTACT WITH APCH CTL; ACFT SUFFERED COMPLETE ELECTRICAL FAILURE CUTTING OFF COMS AND NAV EQUIP IN IMC. PLT CLBED TO 11000 FT FOR TERRAIN CLRNC FINDING VMC BTWN LAYERS. HANDHELD RADIO WAS ON BOARD AND PARTIAL COMS AND NAV WAS RESTORED. ALTHOUGH PLT SQUAWKED 7700; IT IS NOT BELIEVED THAT APCH CTL RECEIVED BECAUSE OF ELECTRICAL PROB AND NON RADAR ENVIRONMENT. BECAUSE APCH INTO TWF WOULD HAVE REQUIRED FLYING INTO IMC WITH ONLY LIMITED RELIABILITY ON PARTIALLY RESTORED ELECTRONICS; PLT REQUESTED AND WAS GRANTED DEV ON IFR FLT PLAN TO LAS VEGAS; MCCLELLEN; THE NEAREST ARPT WITH VFR AND CLR SKIES. PRIOR TO RECEIVING CLRNC TO LAS; ACFT CIRCLED OVER TWF; PROBABLY OFF AIRWAY AND IN CONFLICT WITH ORIGINAL CLRNC. WHEN CLRED FOR ILS APCH INTO TWF; PLT DECLINED. ENRTE TO LAS; GRADUALLY CLBED TO 17000 FT TO AVOID WX. FLT THEREAFTER WENT SOMEWHAT ROUTINE EXCEPT FOR ONE DEV FROM ASSIGNED ALT OF 17000 FT DOWN TO APPROX 15500 FT DUE TO ICE AND WX. ACFT FLOWN WAS A CESSNA 340A. PROBABLE CAUSE OF ENG PROB: BECAUSE ENGS ULTIMATELY SMOOTHED OUT; PLT SURMISES PROB MAY HAVE BEEN CAUSED BY ICE PARTICLES SUSPENDED IN FUEL AND INGESTED DURING INITIAL CLB. ALTHOUGH ACFT ENGS WERE PREHEATED AND RAN NORMALLY DURING RUNUP; FUEL IN WINGS COULD HAVE BEEN BELOW OR AT FREEZING TEMPS. PROB PROBABLY COULD HAVE BEEN AVOIDED THROUGH USE OF DE-ICE ADDITIVE TO FUEL. AS OF THE DATE OF THIS RPT; ELECTRICAL PROB HAS NOT BEEN DIAGNOSED. CONTRIBUTING FACTORS MAY HAVE BEEN HIGH ELECTRICAL LOADS THROUGH PREVENTIVE USE OF DE-ICING EQUIP. PARTIAL ELECTRICAL WAS EVENTUALLY RESTORED THROUGH RESET OF ALTERNATOR CIRCUITS AND ALTERNATING BTWN SYS ON AT ANY ONE TIME. AVAILABILITY OF A HANDHELD RADIO IS CONSIDERED BY THIS PLT TO BE AN IMPORTANT PART OF SAFETY EQUIP. IT DOESN'T DO A GREAT DEAL OF GOOD; HOWEVER; UNLESS THE BATTERY IS FULLY CHARGED. OURS WAS LOW; AND SO IT WOULD ONLY BE USED SPARINGLY.