The pilot of the Piper Chieftain reported that at the top of
descent he noticed that the left engine began to run roughly.
Initial checks showed no evidence of a problem and the pilot began
to troubleshoot. Approximately 30 seconds after the initial onset
of vibrations, the pilot noticed that the left engine oil pressure
and power significantly decreased before the engine failed. The
pilot shut the engine down and feathered the propeller in
accordance with emergency procedures. The pilot broadcast a PIN to
Melbourne Air Traffic Control advising of the situation and that
his intention was to continue to Devonport. After arriving in the
circuit area the pilot ensured that the Rescue Fire Fighting
Service was in attendance and that he had briefed the passengers,
before landing the aircraft without further incident.
A post flight engineering inspection revealed that a number
2-cylinder connecting rod bolt had failed allowing the rod to
puncture the left engine crankcase in two locations.
The failed components were examined by the ATSB technical
analysis section. It was found that the number 2 connecting rod
failure was the result of fatigue cracking of the connecting rod
big-end bearing housing.
The fatigue cracking had initiated and developed due to abnormal
loads arising from the loss of the bearing shell material from
within the connecting rod big-end housing. The connecting rod bolt
failure then occurred due to bending overload , which resulted from
the fatigue cracking and separation of the opposite side of the
big-end bearing housing.
As at 11 September 2001, the ATSB was examining ten engines from
PA 31 aircraft types as part of the ongoing investigation 20002157.
The engine in this occurrence was one of the ten being examined,
however insufficient evidence was available from the items examined
in this occurrence to enable a determination of the mechanism of
the big-end bearing failure.