What happened
On the morning of 12 January 2007, a Safari helicopter, registration ZU-DVY, departed Wonderboom Aerodrome for a private flight to Brits Aerodrome. The flight was conducted under visual flight rules in clear weather conditions. While traversing the Lethlabile area near Rabukalo Village, the aircraft experienced a catastrophic structural failure. Witnesses in the area reported hearing a loud noise followed by the aircraft descending rapidly. The impact and subsequent fire destroyed the helicopter and resulted in the 1 fatality of the pilot.
The investigation
SACAA AIID investigators examined the wreckage and performed metallurgical analysis on the recovered components. The investigation focused on the integrity of the main rotor assembly and the maintenance history of the aircraft. Investigators scrutinized the manufacturing of the rotor head components, the validity of recent inspections, and the legality of modifications made to the airframe. The inquiry also looked into the oversight provided by the civil aviation authority regarding the assembly of this non-type certificated aircraft.
Findings
Technical analysis revealed that the main rotor head spindle failed due to the propagation of a fatigue crack. This failure caused the main rotor blades to separate from the aircraft during flight. Two primary factors contributed to this failure: the spindle was manufactured with a sharp corner lacking an appropriate radius, which acted as a stress raiser, and the component had likely been subjected to a shock overload, such as a rotor strike, at some point in its history. There was evidence suggesting that components from another aircraft, registration ZU-CPO, may have been installed on ZU-DVY.
Furthermore, the investigation identified significant maintenance and regulatory discrepancies. The aircraft had been operated beyond its mandatory 100-hour service interval, and several maintenance releases were found to be invalid. The owner had performed unauthorized modifications, including the installation of an unapproved turbocharger, and had conducted unauthorized maintenance tasks. Additionally, the aircraft lacked a formal Type Acceptance Certificate, and the oversight of the assembly process was deemed inadequate.