SELMA, AL, USA
N3735Y
BEECH A36
DURING CRUISE FLIGHT, THE ENGINE RPM DECREASED, MOMENTARILY. THE PILOT LANDED AND A MECHANIC CHECKED THE ENGINE. NO ANOMALIES WERE FOUND. A POST MAINTENANCE FLIGHT, IN THE LANDING PATTERN, WAS FLOWN TO VERIFY ENGINE OPERATION. ON FINAL APPROACH, THE ENGINE QUIT, AND THE AIRPLANE WAS LANDED IN ROUGH TERRAIN SHORT OF THE RUNWAY. EXAMINATION OF THE ENGINE REVEALED THAT THE NUMBER 2 CHECK COUNTERWEIGHT BLADE WAS FRACTURED. METALLURGICAL EXAMINATION DISCOVERED CORROSION PITTING ON THE INNER DIAMETER OF THE COUNTERWEIGHT PIN BUSHINGS, AS WELL AS EXCESSIVE INNER DIAMETER WEAR. THE COUNTERWEIGHT BLADE FRACTURE EXHIBITED EVIDENCE OF FATIGUE. A LOG BOOK ENTRY INDICATED THAT THE ENGINE HAD BEEN PREVIOUSLY DISASSEMBLED FOR EXAMINATION FOLLOWING A LIGHTNING STRIKE. THERE WAS NO RECORD OF AN ENGINE OVERHAUL. THE SAFETY BOARD BELIEVES THAT THE COUNTERWEIGHT FAILED IN FATIGUE, BECAUSE OF PREVIOUS PITTING DAMAGE TO THE BUSHINGS, FROM AN UNKNOWN SOURCE.
THE FATIGUE FAILURE OF THE ENGINE CRANKSHAFT COUNTERWEIGHT BLADE, WHICH RESULTED FROM EXCESSIVE WEAR OF THE COUNTERWEIGHT PIN BUSHINGS, DUE TO CORROSION FROM AN UNKNOWN SOURCE.
Source: NTSB Aviation Accident Database
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