What happened
On May 21, 2006, during the Swiss Gliding Championships at Bern-Belp Airport, a Ventus cT glider, registration HB-2mal2229, experienced a catastrophic structural failure during its final approach. The pilot was flying a high-speed pass over the finish line at an altitude of approximately 150 to 250 meters.
Witnesses observed the aircraft's wings bending significantly downward for several seconds, accompanied by a forward pitch of the fuselage. Suddenly, the wings flexed upward with great force, and the right wing snapped at the fuselage junction with a loud bang. The remaining fuselage and left wing entered a parabolic descent, striking the ground at a very high velocity. The pilot sustained fatal injuries in the impact.
The investigation
The investigation focused on the structural integrity of the aircraft and the aerodynamic forces acting on the wings during the final moments of flight. Investigators examined the wreckage, the flight data from multiple onboard loggers, and the state of the airspeed indicator, which showed an impact speed exceeding 300 km/h.
Technical analysis of the Ventus cT design revealed that at high speeds, a positive camber (flap) position causes the wingtips to bend downward. The investigation also looked into the mechanical forces required to operate the flap lever at high speeds and the potential for pilot-induced oscillations or sudden load factor changes during flap adjustment.
Findings
- The aircraft was flying at a high speed during the approach to the finish line.
- The wings were observed in a downward-curved position, indicating a positive camber setting at excessive speed.
- The pilot likely attempted to correct the flap position while maintaining high velocity.
- An abrupt change from a positive to a negative flap position caused a sudden shift in lift distribution, resulting in significant negative load factors.
- These sudden aerodynamic forces, potentially compounded by elevator inputs, exceeded the structural strength of the wing spars.
- The right wing failed at the wing root, leading to the loss of control and the subsequent crash.