What happened
On 22 November 2007, a private flight departed from Gariep Dam Aerodrome in the Free State Province, heading toward the Colesberg area. The aircraft, a Nimbus 4DM motor glider with registration D-KRAV, was carrying a pilot and one passenger. At approximately 1530Z, while flying at an altitude of roughly 2,000 m AGL, the glider experienced a catastrophic mid-air structural failure. The aircraft broke apart in the Colesberg district, and the resulting debris field spanned approximately 7 km. Both occupants sustained fatal injuries, and the aircraft was destroyed by the impact and a subsequent post-crash fire.
The investigation
Investigators from the SACAA AIID examined the wreckage, which included the fuselage, engine, and various wing components. Reconstruction of the wing panels revealed that the fractures occurred in a symmetrical pattern on both the left and right sides, indicating the airframe was subjected to a positive g-load failure caused by severe overloading.
The investigation noted that the outer wing tiplets, canopy sections, and portions of the flaps and ailerons were the first components to separate. Evidence from the wreckage suggested that the airbrake mechanism on the right inner wing had been subjected to extreme stress; the airbrake cap and its connecting linkage were found detached from the wing panel. Furthermore, the wing's carbon fibre cap assembly showed signs of scuffing, suggesting the airbrakes may have been extended at high speed.
Findings
- The primary cause of the structural failure is believed to be aerodynamic flutter encountered during high-speed flight, which led to the disintegration of the airframe.
- The aircraft likely encountered high speeds that exceeded its design limitations, causing the wing control surfaces to flutter.
- There is evidence that the airbrake mechanism may have been subjected to excessive loading, potentially due to the airbrakes being deployed or partially deployed at speeds beyond their safe operating range.
- While other scenarios—such as an overstress event during a spin recovery or a mechanical failure of the airbrake linkage—were considered, the high-speed flutter scenario is the most probable cause.