What happened
On August 5, 2016, a Sportine Aviacija Lak17BT motor glider, registered F-CGDT, was performing a local flight at the Châllen-Écury-sur-Coole aerodrome. The pilot was preparing for a winch launch. As the aircraft accelerated down the runway, it experienced a very short ground roll before immediately taking an excessive pitch-up attitude.
Witnesses on the ground observed the aircraft oscillating on its yaw axis at an altitude between 20 and 30 meters. Shortly after reaching this height, the glider abruptly pitched down and collided with the runway surface on its back with high energy. The impact resulted in the destruction of the aircraft and caused one injury to the pilot, who sustained serious injuries and had no memory of the event.
The investigation
The investigation examined the wreckage and the operational conditions of the launch. The aircraft was configured with 21-meter wing extensions, and the engine was properly stowed. The flight controls were found to be continuous, and the wing extensions were correctly attached. The winch operator reported setting the hydraulic winch to 300 bar, a setting typically used for single-seat gliders. Upon noticing the aircraft's unusual attitude, the operator immediately reduced power, which caused the cable to detach.
Post-accident testing of the winch revealed no mechanical anomalies, and the equipment continued to operate normally for subsequent launches during a competition held the following day. Meteorological conditions were favorable, with a light wind of 5 to 10 knots aligned with the takeoff direction and no significant turbulence reported.
Findings
- The primary cause of the accident was an excessive pitch-up attitude during the initial phase of the winch launch.
- This high pitch angle caused the aircraft to climb at a steep angle at the expense of airspeed, leading to a stall under load.
- The low altitude reached during the incident left the pilot with insufficient time to recover control before the ground impact.
- The reduction in winch power by the operator, intended to mitigate the unusual attitude, likely caused the cable to detach during the loss of control.