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Australian Transport Safety Bureau (ATSB) - Australia
Narrative: A Saab 340B aircraft, registered VH-NRX was being operated as RXA768 on a routine passenger flight from Albury, New South Wales (NSW) to Sydney, NSW. On board the aircraft were 16 passengers and 3 crew. About 55 nautical miles south-west of Sydney airport, the crew noticed uncommanded engine indications and began the necessary checklists. While undertaking the checklist items, the crew experienced minor vibrations from the right engine. These vibrations worsened as the checklist progressed and became visually evident to the First Officer. As a result the crew commenced the engine shutdown procedure. During the engine shutdown procedure, the propeller separated from the aircraft. The crew made a Pan-Pan call to air traffic control, and completed the engine shutdown procedure. The aircraft landed without incident at Sydney airport.
An inspection of the aircraft by the ATSB at Sydney airport identified that the propeller shaft had fractured, leading to the separation of the propeller.
On 21 March 2017, the NSW Police Aviation Support Branch (PolAir) undertook a search operation for the separated propeller. The propeller was located in an area under dense forest about 8NM south-west of Sydney airport. The propeller was found with the flange section of propeller shaft secured to the propeller assembly and a fracture through the propeller shaft.
An inspection of the propeller revealed a fatigue fracture that began in the propeller mounting flange (the part that attaches the propeller to the gearbox) and continued into the propeller shaft. The inspection also found corrosion near the initiation of the fracture.
The ATSB stated that this was the first known critical failure of this type, initiating within the propeller hub flange of the GE Aviation CT7-9B engine.
The ATSB's ongoing investigation will focus on maintenance procedures associated with the propeller gear box shaft and examine factors that may have contributed to the fatigue fracture at the propeller mounting flange.