What happened
On 28 November 2008, a pilot and his seven-year-old son were conducting a private flight in the Cullinan area of Mpumalanga province. While flying at approximately 5,000 ft AMSL, the passenger spotted wildlife and requested a descent to get a better view. The pilot descended to roughly 100 ft above the ground. During a subsequent 360-degree turn, the aircraft experienced a sudden loss of altitude and struck the ground. The pilot sustained severe injuries to his spine and arm, while the passenger suffered minor injuries. The aircraft, an experimental Thunderbolt microlight, sustained substantial damage to its undercarriage.
The investigation
An investigation into the accident revealed that the aircraft was a homebuilt, experimental prototype that was not yet registered with the South African Civil Aviation Authority (SACAA). At the time of the crash, the aircraft lacked a valid Authority to Fly or a Proving Flight Authority. The investigation also noted that the pilot, while holding a valid microlight license and medical certificate, was not type-rated for this specific prototype. The weather during the occurrence was reported as calm with good visibility and a temperature of 28°C.
Findings
- The primary cause of the accident was the pilot performing a 360-degree turn, which caused the delta wing to generate a large wake vortex.
- The aircraft encountered its own wake vortex, which disturbed the airflow over the wing and led to a loss of lift and a subsequent stall.
- The aircraft was being operated illegally as it was not yet registered and lacked the necessary flight authorities.
- The pilot was not specifically type-rated for the experimental Thunderbolt model.