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A Jabiru aircraft’s wooden propeller separated in flight due to extensive fatigue cracking resulting in the fracture of the propeller bolts, an ATSB transport safety investigation details.
An instructor and student pilot had been conducting circuit training in the Jabiru J120-C aircraft at Devonport Airport, Tasmania on 16 January 2022.
While on the downwind leg of a circuit, the student pilot (seated in the left seat) saw a white flash and called ‘seagull’, believing they saw a bird. At the same time, the instructor felt a jarring and saw that the propeller had separated from the aircraft.
The engine RPM immediately increased as the engine was unloaded, however there was no other unusual noise, vibration or indications associated with the propeller separation.
The instructor immediately took control of the aircraft, closed the throttle and conducted an unpowered landing onto the runway. The propeller was subsequently found, on the beach adjacent to the airport, with the tip of one of the blades separated.
“The ATSB’s investigation determined that the propeller separation occurred as a result of fracture of the propeller bolts,” said ATSB Director Transport Safety Dr Stuart Godley.
Examination of the propeller found no evidence of a defect at the fractured tip, while there was no observed organic matter or smearing to indicate a bird strike.
“The propeller bolts showed extensive fatigue crack propagation. Regardless of whether or not the propeller struck a bird, the extent of cracking was such that the propeller could have separated without an external influence, or would have separated with continued operation.”
The investigation also found that propeller washers had not been installed in accordance with the maintenance manual, and this may have contributed to accelerated wear and subsequent cracking of the bolts.
“This incident and investigation highlights the importance of conducting maintenance and thorough inspections of hardware in accordance with the manufacturer’s requirements and recommendations, as deviations can have unintended, and potentially hazardous consequences,” said Dr Godley.
“Particular attention should be paid to evidence of abnormal contact or movement between components as indications of loose or fretting components.”
Dr Godley noted that the ATSB did not typically investigate accidents and incidents involved recreational aircraft registered with Recreational Aviation Australia (RAAus), however Australia is the state of design and manufacture for the Jabiru aircraft. As such the ATSB investigated this incident to determine if there were broader implications of the international Jabiru aircraft fleet.
Read the report: In-flight propeller loss involving Jabiru J120, 23-1531 Devonport Airport, Tasmania, on 16 January 2022