PLT OF AN SMA SEL LOST PWR DURING AN IFR FLT RESULTING IN AN OFF ARPT LNDG WHEN THE ENG QUIT.

Narrative

WHILE IN CRUISE; LEAVING HELON INTXN TOWARDS IGN VOR ON AIRWAY V58; ENG RPM DROPPED FROM CRUISE OF 2500 RPM TO 2000 RPM. UNTIL THIS POINT THE ACFT HAD BEEN PERFORMING NORMALLY SINCE DEP FROM CGF; 3.5 HRS PRIOR. FLT CONDITIONS WERE IMC IN CLOUDS; TOPS UNDETERMINED BASES AT 2000 FT. OUTSIDE AIR TEMP WAS 10 DEGS WITH NO ICE OBSERVED ANYWHERE ON ACFT. THESE CONDITIONS HAD BEEN SIMILAR FOR THE PRIOR HR BEFORE THE ENG MALFUNCTION. FLT WAS SMOOTH. IMMEDIATELY UPON EXPERIENCING THE RPM DROP; THE PLT NOTIFIED ATC OF THE PROB AND BEGAN EMER PROCS. ATC VECTORED THE ACFT TO AN ILS 5 APCH AT SWF AND INSTRUCTED A DSCNT FOR THE APCH. PLT WAS GIVEN MORE VECTORS TO SET UP THE APCH. AFTER PASSING THROUGH APPROX 5000 FT; THE ENG RPM DROPPED FURTHER TO 1400 RPM. AS IT BECAME INCREASINGLY DIFFICULT TO HOLD A SHALLOW DSCNT THE PLANE LOST MORE ALT. THE PLANE BECAME ESTABLISHED ON THE ILS AT 3000 FT ABOUT 11 MI OUT FROM THE ARPT. WE WERE NOT ABLE TO HOLD ALT TO MAINTAIN ON THE GS. IT WAS APPARENT WE WOULD NOT MAKE SWF. AFTER ADVISING ATC WE WERE VECTORED TO MGJ ABOUT 6 MI AWAY. AT BTWN 2500-2000 FT WE DSNDED THROUGH THE BASES AND OBSERVED THE FIELD ABOUT 4 MI DISTANT. WE CONTINUED TOWARDS MGJ AND SELECTED A RWY. AT 1500 FT MSL THE ENG STOPPED COMPLETELY AND DEVELOPED NO PWR WITH THE PROP WINDMILLING. WE DETERMINED WE WOULD NOT HAVE ENOUGH ALT TO MAKE MGJ AND SELECTED A FIELD 1/2 MI FROM MGJ. ON SHORT FINAL TO THE FIELD THE PLANE CLIPPED A FEW TREES AT THE END OF THE FIELD; HITTING THE TOP 2 FT OF THE TREE'S SMALLER BRANCHES CAUSING MINOR DAMAGE TO THE R WING ROOT AND STABILATOR. OTHERWISE THE PLANE LANDED SAFELY WITH NO FURTHER DAMAGE AND NO INJURIES.