What happened
On 22 December 2007, a Schleicher ASW 20A glider, registration ZS-GND, was winch-launched from the Goldfields Gliding Club at Hennenman, Free State. Following the launch, the pilot flew a route passing over Virginia and Ventersburg before returning toward the Hennenman Aerodrome. During the flight, the pilot communicated with another glider pilot, stating they were simply flying around the area.
Data from a GPS logger recovered from the wreckage reveals that at approximately 13:13Z, the aircraft was flying north-northwest at an altitude of 2,621 feet. During this period, the aircraft's speed and descent rate began to increase rapidly. The logger indicates the glider entered a barrel-type maneuver or skewed loop, which was followed by a significant increase in speed and a subsequent high-G load. A local tractor driver reported hearing the sound of the aircraft breaking up in the air. The main wreckage was located in a ploughed maize field roughly 3 km south of Hennenman Aerodrome. The pilot sustained fatal injuries.
The investigation
SACAA AIID investigators examined the wreckage and recovered a Cambridge GPS data logger. The investigation focused on the flight path, the physical condition of the airframe, and the aerodynamic forces acting on the aircraft during the final moments of flight. The wreckage was found spread over a 1.5 km area, indicating an in-flight breakup at an altitude of approximately 1,500 meters (4,800 feet) AGL.
Investigators analyzed the structural integrity of the wings and the control surfaces. The investigation also reviewed the aircraft's maintenance records, which showed the aircraft had a valid authority to fly and had undergone a recent annual inspection. Meteorological data from the day indicated hot temperatures and moderate turbulence, which may have influenced the aircraft's aerodynamic behavior during maneuvers.
Findings
- The aircraft experienced high-speed flutter in the control surfaces, specifically involving the flapperons.
- The investigation established that the glider reached speeds that likely exceeded its structural limits, leading to excessive g loading.
- Evidence of symmetrical loading was found on the wings, where both wing panels fractured under extreme bending loads.
- The flutter damper, while functional, was torn from its mounting due to the intensity of the structural failure.
- The aircraft's clean aerodynamic design likely contributed to rapid acceleration during the aerobatic maneuver, making speed control difficult.
- The structural breakup was so severe that the wings eventually separated from the fuselage, causing the remaining fuselage to dive into the ground.