CROSSVILLE, TN, USA
N7613J
PIPER PA-28R-180
ON TAKEOFF THE PLT SAW AN OIL LEAK AROUND THE PROP HUB. THE ACFT WAS RETURNED TO THE AIRPORT AND THE PROP GOVERNOR OIL TUBE FITTING WAS FOUND TO BE CRACKED. THE PART WAS REPLACED AND THE FLT WAS CONTINUED. THE PART WAS CHECKED DURING A LATER REFUELING STOP AND WAS NOT FOUND TO BE LEAKING. DURING CRUISE IN MOUNTAINOUS TERRAIN AN OIL LEAK WAS AGAIN SEEN. VECTORS WERE RECEIVED TO A NEARBY ARPT. THE ENG QUIT AND THE PLT ATTEMPTED AN EMERGENCY LANDING DURING WHICH THE ACFT STRUCK A TREE. EXAMINATION OF THE ENG SHOWED THAT THE OIL LINE FITTING HAD AGAIN CRACKED. BOTH FITTINGS WERE FOUND BY METALLURGICAL EXAMINATION TO HAVE FAILED DUE TO A LOW STRESS HIGH CYCLE FATIGUE INDUCED BY A HIGH MEAN TENSILE STRESS. THE OIL LINE WAS FOUND TO BE UNRESTRAINED ALTHOUGH THE SERVICE MANUAL CALLS FOR TWO CLAMPS. THE RESULTING VIBRATION INDUCED THE STRESS LOADS AS SEEN ON THE TWO FITTINGS.
Source: NTSB Aviation Accident Database
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