What happened
On October 26, 2024, at approximately 13:50 JST, an Alexander Schleier ASK21 glider, registration JA21YP, was conducting specialized emergency maneuvers near the Naganoshi Glider Site in Nagano Prefecture. The flight, operated by the Nagano Gliding Association, was intended to simulate a loss of towing force from a winch at a low altitude.
During the climb phase, the trainee pilot released the tow line after the winch power was cut. While the trainee initially attempted to land on the runway, the instructor took control to execute a forward slip to increase the descent rate. However, the instructor determined that the glider's momentum and the remaining runway distance made a safe runway landing impossible without risking a dangerous ground loop or an overrun into a pavement step-down.
To avoid these hazards, the instructor opted to abort the runway landing and steer the aircraft toward a grassy area northeast of the runway. During a left turn intended to avoid trees and an elevated bridge, the left wingtip struck vegetation. The aircraft subsequently touched down while rotating left and skidded to the right, with the nose colliding with trees and plants. There were no injuries to the instructor or trainee, but the aircraft sustained significant damage, including cracks in the left fuselage skin, the left wing leading edge, and a broken rear seat canopy.
The investigation
The JTSB investigation focused on the flight dynamics, the winch operations, and the safety protocols of the training session. Investigators analyzed the meteorological conditions, which were clear with minimal wind, and the technical specifications of the runway length.
Key areas of examination included the timing of the winch operator's decision to stop winding and the lack of standardized safety parameters for such high-risk training. The investigation also reviewed the association's procedures for defining safe operating envelopes for emergency simulations.