What happened
On 23 August 2009, a Mistral-C sailplane, registration OO-ZTV, was being towed from runway 17 at the Goetsenhoeven airfield. The takeoff process began normally, but once airborne, the sailplane began a series of pitching oscillations, commonly known as porpoising. During this sequence, the aircraft struck the runway pavement two or three times.
The final downward movement was particularly violent, causing the aircraft's wing to strike the runway surface. Following this impact, the pilot released the tow cable. After the release, the sailplane entered a right-hand roll, eventually becoming inverted and crashing on its back on the right side of the runway. The pilot sustained serious injuries, including a head fracture.
The investigation
Investigators examined both the OO-ZTV sailplane and the towing Piper PA-18, registration OO-VVC. Technical inspections confirmed that both aircraft were airworthy prior to the accident and that the towing mechanism, including the weak link, was fully operational. The damage to the sailplane was determined to have been caused solely by the impact with the ground.
The investigation also analyzed the environmental conditions. On the afternoon of the accident, strong thermal activity was present due to high temperatures (28°C), which can induce turbulence over a dark runway. The investigators also reviewed the pilot's flight history, noting that while the pilot was qualified, they had very limited experience with composite-structure aircraft compared to their extensive background in wood and fabric models.
Findings
- The primary cause of the accident was the porpoising movement of the sailplane during takeoff, which led to a heavy collision with the runway and subsequent loss of control.
- Strong thermal activity contributed to the instability during the takeoff phase.
- The pilot's limited experience with the specific handling characteristics of modern composite-structure sailplanes was a contributing factor.
- Structural damage to the right wingtip following the runway impact may have contributed to the aircraft's inability to maintain a straight flight path after the tow cable was released.