What happened
On 8 August 2015, a private flight departing from Avontuur Airfield in the Western Cape ended in an aircraft accident. The pilot and a passenger were attempting to fly to Graaff-Reinet for an annual aircraft inspection. After completing a pre-flight check and taxiing to Runway 06, the pilot began the takeoff roll.
As the RAF 2000 GTX SE F1 reached a height of approximately 3 to 3.5 meters above the ground, the pilot experienced severe vibrations and a sudden loss of control. The aircraft sank and struck the runway, causing substantial damage to the airframe. Both the pilot and the passenger sustained minor injuries and were able to evacuate the wreckage.
The investigation
Investigators examined the wreckage and the rotor assembly to determine why the aircraft became uncontrollable. During the takeoff, a witness observed a loud bang followed by the separation of the rotor blades. One winglet was thrown to the left side of the runway, while the other landed on the right side.
Technical scrutiny of the aircraft's maintenance history revealed several discrepancies. The logbooks lacked complete records regarding a previous rollover accident from 2013, and there were missing entries for mass and balance updates and compass swing certifications. Additionally, the investigation noted that the engine instrumentation used different units and markings than those specified in the flight operations manual.
Findings
The investigation established that the primary cause of the accident was the fatigue failure of a high-strength hex head shear bolt within the rotor hub bar assembly. Metallurgical analysis confirmed that the bolt broke due to fatigue caused by repeated reverse bending loads in the horizontal/lead-lag operational plane.
Contributing to the failure was improper maintenance, specifically the failure to replace the old bolt with a new one during the assembly process. It was also noted that while the rotor hub bar assembly installations should be performed exclusively by the manufacturer, the winglets had been installed by an approved person following a period when the aircraft was transported by road without them attached.