What happened
On October 10, 2021, a solo training flight involving an Alexander Schleicher ASK13 glider, registration JA2189, resulted in an accident at the Aso Temporary Airfield in Kumamoto Prefecture. The flight was being conducted by a trainee pilot under the ground-based supervision of an instructor.
During the landing sequence, the trainee initiated a base turn that was wider than the standard traffic pattern due to being at a higher altitude than usual at the checkpoint. This decision significantly lengthened the final approach, increasing the distance from the touchdown point from the typical 600 meters to approximately 900 meters. Consequently, the approach path became lower than intended.
As the glider approached the ground, it encountered turbulent wind conditions caused by gusts blowing over a nearby hill. While attempting to align the aircraft with the runway, a right-hand gust caused the glider to bank. The trainee attempted to correct this with left-hand input, but overcontrol caused the aircraft to bank too far to the left. Upon touchdown, the glider was facing the leeward direction and drifted off the runway, striking a shrub. The impact caused substantial damage to the left wing, while the subsequent movement of the tail section caused the tail wheel to buckle the aircraft's steel pipe structure.
The investigation
The JTSB investigation examined the flight logs, meteorological data, and the aircraft's flight path. Investigators analyzed the terrain surrounding the Aso Temporary Airfield, noting that the southeastern approach path is bordered by high terrain that generates disturbed wind. The investigation also reviewed the trainee's proficiency and the specific maneuvers performed during the final approach, including the use of the crab method and the transition to a side slip.
Findings
- The trainee's decision to extend the base turn resulted in an approach path that was too low and too long.
- Although the recorded wind was within the official safety criteria for solo flight, the presence of turbulent wind from the nearby hills created challenging conditions for a trainee.
- The pilot's attempt to correct for a sudden gust led to overcontrol, leaving the aircraft improperly aligned for touchdown.
- At the moment of touchdown, the glider's speed was insufficient for the rudder to effectively counteract the leftward deviation.