What happened
On 19 April 2012, a Falco F8L aircraft, registration ZU-BTT, departed from Kimberley Aerodrome for a private flight to Beaufort West. The flight proceeded normally for approximately 1.85 hours until the aircraft reached the cruise phase. While cruising at 145 knots with the engine running at 2500 RPM, the propeller suddenly detached from the engine attachment flange.
Upon separation, the propeller struck the engine cowling and the left wing, causing substantial damage to the airframe. The pilot managed to execute a controlled forced landing on the N12 National road, approximately 50 km south of Victoria West. At the time of the landing, the road was clear of traffic. Following the landing, the aircraft was moved to a nearby gravel road. There were 0 fatalities and 0 injuries among the two occupants.
The investigation
SACAA AIID investigators examined the wreckage and the components involved in the failure. The investigation focused on the six bolts used to secure the propeller to the engine ring gear. Metallurgical analysis of the fractured bolts revealed that the failure was caused by fatigue. Specifically, the examination identified crack-like lap defects within the thread roots, which were created during the thread rolling process.
Further inquiry into the origin of the hardware revealed that the bolts were sourced from a private, non-aviation supplier rather than an approved aviation component manufacturer. While the pilot, who was also the aircraft owner, had selected the bolts based on their perceived suitability, the investigation noted that the manufacturing standards of these fasteners likely did not meet the rigorous requirements for aviation-grade components.