M20F ACFT ENCOUNTERED ICING RESULTING IN ROUGH RUNNING ENG. RPTR PLT HAD TO DSND BELOW MVA IN ORDER TO REGAIN THE ENG AT WHICH TIME HE WAS DIVERTED TO A VFR ARPT BY CTR CTLR.

Narrative

THE INCIDENT FLT WAS THE SECOND OF A 2-LEG TRIP. ON THE FIRST LEG; TRACE RIME ICE WAS ENCOUNTERED AT 10000 FT NEAR THE TOPS OF A BROKEN LAYER. IT WAS FELT THAT FLYING AT 12000 FT OUTBOUND WOULD GET US ABOVE THE TOPS OF THE ICING CLOUDS; WHICH WAS TRUE FOR A WHILE. WE EVENTUALLY GOT TO THE SOLID LAYER AT 12000 FT; WHERE THE TEMP WAS - 16 DEGS C. WE SAW LITTLE EVIDENCE OF ICING UNTIL THE ENG STARTED RUNNING ROUGH AND LOSING RPM. IN A SHORT TIME; MOST PWR WAS LOST; AND WE BEGAN DSNDING BELOW MEA AND MVA TO REACH A DIVERT ARPT. AFTER MESSING WITH THE ENG CTLS ENOUGH; PWR WAS REGAINED AT APPROX 500-1000 FT BELOW MVA (WE HAD DECLARED AN EMER BY THIS POINT). A CLB WAS POSSIBLE ABOVE MVA; AND THE CTR CTLR VECTORED US TO A VFR FIELD (TUCSON) WITH AN ILS. THE SCARIEST PART OF THE WHOLE EPISODE IS THAT I'M STILL NOT SURE WHAT MADE US LOSE PWR. NO CARB; SO NO CARB ICE -- EITHER INDUCTION ICING OR PROP ICE. THROTTLE MANIPULATION SEEMED TO HELP THE MOST. THE PROB WAS CAUSED BY MY LACK OF EXPERIENCE IN WINTER/MOUNTAIN FLYING; AND BY THE FAILURE TO DIVERT IMMEDIATELY WHEN EVEN TRACE ICE WAS ENCOUNTERED. WE MANAGED TO DELUDE OURSELVES INTO THINKING WE WEREN'T PICKING UP MUCH ICE BY LOOKING AT THE WINDSHIELD AND WINGS. WHILE THERE WAS ENOUGH ICE TO FAIL THE ENG AND EVEN BREAK OFF OUR COM #1 ANTENNA (WHICH THANKFULLY REMAINED INTACT THROUGH APCH AND LNDG WITH A FEW THREADS OF FIBERGLAS). THIS EPISODE WILL MAKE ME STUDY WINTER WX FLYING; AND LISTEN TO THE EXPERTS WHEN THEY SAY TO GET OUT OF ICE AS SOON AS YOU SEE ANY OF IT.