PLT OF AN SMA SEL LOST ACFT CTL WHILE IN ICING CONDITIONS; AND REGAINING ACFT CTL AFTER LOSING 4000 FT OF ALT.

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WHILE IN CRUISE ON TOP OF LAYER (HIGH CIRRUS LAYER MUCH FARTHER ABOVE); WE WERE ENGULFED BY A RISING AND BUILDING CLOUD HEAD. NO ICING WAS FORECAST. WHILE WITHIN THE CLOUD WE WERE ACCUMULATING ICE QUICKLY ON ALL LEADING EDGES AND FRONT WINDOWS. PITOT HEAT WAS ON PRIOR TO ENTRY OF CLOUD. AFTER ABOUT 90 SECONDS WE HAD NOT EXITED THE OTHER SIDE; WE EXECUTED A 180 DEG TURN IN AN ATTEMPT TO EXIT THE ICING CONDITIONS. SHORTLY AFTER EXECUTING THE TURN; WE LOST INDICATIONS OF AIRSPD (140 TO 0 INDICATED IN ABOUT 15 SECONDS) AS WELL AS ALL OTHER PITOT-STATIC INSTS. CTL OF THE ACFT WAS LOST AND WE DSNDED FROM 20000 FT TO 16000 FT BEFORE CTL WAS REGAINED. EMER WAS DECLARED DURING THIS TIME. WE WERE STILL IMC WHEN CTL WAS REGAINED AT 16000 FT BUT WE HAD A MODERATE ICING PROB ON THE ACFT. WE CONTINUED OUR CTLED DSCNT BELOW ASSIGNED ALTS AND BELOW MVA WHILE BEING VECTORED TOWARD MMH ALONG AIRWAYS. THIS WAS NECESSITATED BY THE CONTINUED ACCUMULATION OF ICE. WE BROKE OUT AT 12300 FT OVER MONO LAKE. WHILE CONTINUING OUR NOW VMC DSCNT TOWARD MAMMOTH ARPT WE PARTIALLY LOST PWR (PROBABLY DUE TO INDUCTION ICE UP). ALTERNATE AIR DID LITTLE TO RESTORE FULL PWR. THE WINDSHIELD WAS COMPLETELY FROZEN OVER. WE LANDED SAFELY AT MMH BY UTILIZING PERIPHERAL VISION OUT OF THE SIDE WINDOWS. THE LOSS OF CTL WAS DUE TO FIXATION ON THE AIRSPD INDICATOR PROB AND NOT PROPERLY XCHKING MY OTHER INSTS. ABOUT 10 SECONDS ELAPSED BTWN LOSS OF CTL AND THE REALIZATION THAT A PITOT-STATIC BLOCKAGE HAD OCCURRED. I HAVE PRACTICED PARTIAL PANEL ON MY MOST RECENT INST-COMP CHK. EXPERIENCING THIS FAILURE IN ACTUAL CONDITIONS AND STRUGGLING TO MAKE SENSE OF THE INSTS IS QUITE DIFFERENT FROM AN INSTRUCTOR OBVIOUSLY COVERING AN INST. I DID NOT UTILIZE THE ALT-STATIC VALVE; DUE TO HAVING TO QUICKLY HANDLE THE LOSS OF CTL. I HAVE RECEIVED A CRASH (NO PUN INTENDED) COURSE IN INST FAILURES IN ACTUAL CONDITIONS. THIS WAS MY FIRST EXPERIENCE IN SUCH. THE NEXT TIME IT HAPPENS I'LL BE MUCH MORE PREPARED. I DON'T THINK FIXATION ON ANY ONE INST WILL OCCUR AGAIN.