PVT INST RATED PLT OF AN SMA SET OVERSHOT DSCNT ALT ASSIGNMENT DUE TO A DISTR OF A PARTIAL ENG PWR LOSS.

Narrative

SHORTLY AFTER GIVEN ASSIGNED ALT OF 3000 FT (FROM 4000 FT); AN UNEXPLAINED DROP IN RPM WAS NOTICED. I BECAME DISTRACTED AS I EMPLOYED CARB HEAT; SET MIXTURE TO FULL RICH; CHKED THE PRIMER AND ADJUSTED THE THROTTLE FRICTION. I DID NOT STOP THE DSCNT AT 3000 FT; BUT CONTINUED TO 2300 FT. THE IMPROPER ALT WAS NOTICED AT 2300 FT AND I BEGAN AN ASCENT TO 3000 FT. DETROIT APCH BROUGHT THE ALT TO MY ATTN AS WELL; AND REMINDED ME OF THE CORRECT ALT. THE MAJOR FACTOR ON THIS INCIDENT WAS THE DISTR AND MY FAILURE TO MONITOR THE ALTIMETER AS THE RPM PROB WAS DIAGNOSED. THE FLT WAS UNEVENTFUL AFTER THE RETURN TO 3000 FT. NO ADDITIONAL RPM PROBS WERE NOTED; AND WE PROCEEDED TO FLINT AFTER DOING A MISSED APCH AT PONTIAC (CEILING BELOW DIRECTIONAL GYROSCOPE). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE WAS OPERATING A CESSNA 172 DURING THIS INCIDENT. HE BELIEVED THAT THE PWR LOSS WAS DEFINITELY DUE TO ENG INTAKE ICING SINCE THE PWR WAS REGAINED AFTER A BRIEF PERIOD OF CARB HEAT APPLICATION. HE REALIZES THAT OP OF A SEL ENG ACFT IN LOW WX CEILING SITS COULD BE HAZARDOUS SINCE THERE WOULD BE NO OPPORTUNITY TO SELECT THE BEST POSSIBLE LNDG SITE. THERE WAS A SAFETY PLT ON BOARD.