A student pilot and instructor watched on as the wooden propeller on their aircraft flew off as they were conducting circuit training.
An ATSB investigation revealed how the instructor took control of the Jabiru J120-C and landed the aircraft at Devonport Airport in Tasmania.
The incident took place in January 2022, and the propeller was eventually 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 the organisation’s director of transport safety, Dr Stuart Godley.
The full report reveals how 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.
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 ATSB however said it “could not discount” the observations of an apparent bird strike and said it was “possible” it caused the propeller to separate.
“The propeller bolts showed extensive fatigue crack propagation,” said Dr Godley. “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.
“Particular attention should be paid to evidence of abnormal contact or movement between components as indications of loose or fretting components.”