What happened
Shortly after reaching cruise altitude, the pilot experienced a loud noise followed by noticeable vibration originating from the left engine. In response to these indications, the pilot shut down the left engine and initiated a return to the departure airport.
Upon landing, an inspection of the aircraft revealed that approximately eight inches of the propeller blade tip attached to the left engine had separated during flight. The detached fragment impacted the nose section of the airplane, damaging a former in the structure. The debris then traveled into the right engine nacelle. A small nick was observed on the remaining blade surface, which coincided with the fracture plane.
The investigation
The examination focused on the separation of the propeller blade tip and the resulting damage to the airframe. Investigators noted the specific location of the damage in the nose section and the right engine nacelle. The presence of a small nick on the remaining blade surface provided context for the fracture mechanism.
Findings
The primary finding was the separation of approximately eight inches of the propeller blade tip from the left engine. This failure resulted in structural damage to the nose former and intrusion into the right engine nacelle. The investigation identified a small nick on the remaining blade surface that aligned with the fracture plane as a key factor in the failure event.