What happened
During the climb to cruise phase of flight, the pilot experienced a sudden loss of one blade from the three-bladed right-hand propeller. The failure occurred while the aircraft was gaining altitude, resulting in immediate mechanical compromise of the propulsion system.
The investigation
A detailed examination of both the propeller assembly and the associated engine was conducted to determine the root cause of the incident. Technical analysis revealed that critical components were missing from the engine assembly. Specifically, the crankshaft counterweight bushings had not been installed during previous maintenance or assembly work.
The absence of these bushings allowed high-frequency vibration to develop within the engine structure. This persistent and severe vibration was directly responsible for the structural failure of the propeller hub. The mechanical stress caused by the unmitigated vibration led to the disintegration of the hub, which in turn resulted in the separation of the propeller blade.
Findings
The investigation identified a specific maintenance error as the primary contributing factor. The failure was not due to material defect or operational overload, but rather the omission of essential hardware.
- Missing crankshaft counterweight bushings were found to be absent from the engine assembly.
- High-frequency vibration existed in the engine due to the missing components.
- Propeller hub failure was caused by the sustained vibration.
- One propeller blade separated during the climb phase.