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