PHILADELPHIA, PA, USA
N66LA
MITSUBISHI MU-2-60
AT 6000 FEET MSL, WHILE IN CRUISE FLIGHT, A PROPELLER BLADE FROM THE LEFT PROPELLER ASSEMBLY SEPARATED IN-FLIGHT, PENETRATED THE FUSELAGE, BREAKING ELECTRICAL LINES AND CAUSING A LOSS OF ELECTRICAL POWER. AT THE TIME THE AIRPLANE WAS IN IMC, SO THE PILOT ELECTED TO TURN 180 DEGREES IN AN ATTEMPT TO FLY TO AN AREA OF BETTER WEATHER. HE FLEW WITHOUT ELECTRICAL POWER OR MOST OF THE INSTRUMENTS FOR ABOUT 40 MINUTES, UNTIL REACHING AN AREA OF CLEAR WEATHER. ONCE THE PILOT WAS ABLE TO IDENTIFY HIS LOCATION HE ELECTED TO MAKE A GEAR UP LANDING AT THE NEAREST AIRPORT. METALLURGICAL EXAMINATION OF THE SEPARATED BLADE REVEALED THAT THE SEPARATION OF THE BLADE WAS THE RESULT OF FATIGUE CRACKING THAT INITIATED FROM MULTIPLE SITES LOCATED AT CORROSION PITS IN THE BALANCING HOLE. IT WAS DETERMINED THAT THE CORROSION PITTING HAD NOT BEEN DETECTED DURING THE LAST OVERHAUL AND PROCEDURES TO SHOT PEEN AND PAINT THE BALANCING HOLE WERE NOT PERFORMED.
THE IN-FLIGHT SEPARATION OF A PROPELLER BLADE AS A RESULT OF FATIGUE CRACKING INITIATED FROM MULTIPLE SITES LOCATED AT CORROSION PITS IN THE BALANCING HOLE. CONTRIBUTING FACTORS IN THE ACCIDENT WERE: THE FAILURE TO DETECT THE CORROSION DURING THE LAST OVERHAUL PROCEDURE; AND A COMPLETE LOSS OF ELECTRICAL POWER AS RESULT OF THE SEPARATED BLADE BREAKING THE ELECTRICAL LINES.
Source: NTSB Aviation Accident Database
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