What happened
On November 10, 2017, at the Ono Gliding Field in Gifu Prefecture, a Schempp-Hirth V.L. Discus CS glider, registered JA05KG, was participating in a familiarization flight. During a winch launch, the pilot maintained a low nose attitude to prevent an excessive climb, but this resulted in the aircraft failing to transition into a normal climbing attitude. Sensing an abnormality in the towing power, the pilot decided to abort the launch and release the towline at an altitude of approximately 30 meters.
Following the release, the pilot attempted to land the aircraft. However, the pilot did not deploy the air brakes and struggled to manage the aircraft's high airspeed. The flight path drifted toward the winch area, and the pilot's attempts to control the pitch led to pilot-induced oscillations (PIO), characterized by a repetitive bouncing motion. Ultimately, the glider's right main wing struck the winch at approximately 1.2 meters above the ground, causing the aircraft to roll over and come to rest upside-down. The impact destroyed the aircraft.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight history, the pilot's training background, and the mechanical state of the aircraft. The investigation focused on the pilot's decision-making during the aborted launch, the lack of emergency procedure rehearsal, and the aerodynamic behavior of the high-performance glider during the landing approach. Investigators also reviewed the training protocols provided by the Japan Students Aviation League regarding winch launching and emergency responses.
Findings
- The pilot's lack of recent experience with this specific high-performance model led to an excessive nose-down attitude during the initial phase of the launch.
- The pilot failed to deploy the air brakes during the landing approach, which prevented the necessary increase in drag and reduction in lift.
- The pilot's overcontrol during the landing flare caused pilot-induced oscillations (PIO), making the aircraft unstable and difficult to manage.
- A lack of specific training for low-altitude towline release emergencies contributed to the pilot's inability to execute a calm and effective response.
- The pilot's focus on avoiding obstacles led to a flight path that placed the aircraft in close proximity to the winch.