Piper PA-31-350, VH-TTX

While climbing through 600ft after take-off, the left engine of a Piper Chieftain failed. The pilot then completed the engine failure drill, shut down the engine and feathered the propeller. He then returned the aircraft to Bathurst Island.

Initial company engineering examination found that the crankshaft in the left engine had failed. The engine was removed and forwarded to the ATSB for examination.

During disassembly of the engine, the crankshaft was found to have failed at the shoulder of the number three main bearing journal and also through the throw of the number four crank arm. When separating the crankcase halves, it was noted that the main crankcase through studs had lost the fastening torque on all of the securing nuts. That allowed the studs to move within the crankcase stud housings and the crankcase halves to move relative to each other. Fretting wear of the stud non-threaded sections was evident from the resultant movement of the crankcase halves. Examination of the technical records for the engine showed that it had undergone a top overhaul inspection 231.9 hours prior to the crankshaft failure.

The ATSB Technical Analysis team examined the broken crankshaft segments. The analysis determined that the crankshaft fracture was caused by fatigue crack growth through the number three main bearing journal and the number four connecting rod crankarm. Fatigue cracking initiated at the forward fillet of the number three main bearing journal and was associated with surface damage created by contact with the number three main bearing inserts during engine operation. It was evident that those main bearing inserts had moved forward in their housing during engine operation, but they had not rotated in the housing.

Secondary fatigue cracking had initiated at the forward fillet of the number three connecting rod journal and extended a short distance into the number three connecting rod and number three main crankarm. Final fracture in that crankarm occurred as a result of the presence of the small fatigue crack and abnormal loading following the fracture of the number three main and number four rod crankarm.

A summary of broader issues involving this engine failure and similar engine failure occurrences is in the ATSB's report 200002157.