What happened
On March 17, 2016, a privately owned PZL-Bielsko SZD-50-3 Puchacz glider, registration JA50KM, was conducting an aero-tow flight training session from Otone airfield. The flight, which included an instructor in the rear seat and a trainee in the front, was the second flight of the day for the crew. After departing from the tow plane at an altitude of approximately 3,000 feet, the glider was observed by another pilot flying toward the south of the airfield.
At approximately 12:20 JST, the glider entered a residential area in Sakae-town, Inba-gun, Chiba prefecture. Witnesses near the site reported seeing the aircraft in a steep, nose-low, rotating posture, followed by a diving motion. The glider struck the roofs of two houses, causing significant damage to the structures and the destruction of the aircraft. Both the instructor and the trainee sustained fatal injuries due to the impact.
The investigation
The Japan Transport Safety Board (JTSB) examined the wreckage and interviewed witnesses to reconstruct the flight path. Investigators noted that the aircraft's airbrakes were found in the extended position, though the exact timing of this deployment could not be determined due to the severity of the impact. The investigation also reviewed the aircraft's maintenance history, noting that the glider had undergone repairs following a submersion incident in 2015 and had passed a recent airworthiness inspection.
Analysis of the crash site indicated that the aircraft was likely banked to the left with a low nose attitude at the moment of impact. The investigators also considered the meteorological conditions, noting that the area's residential density often generates thermals, which can influence flight dynamics.
Findings
- The aircraft likely entered a spin and was unable to recover before impacting the ground.
- The entry into the spin may have been caused by a stall during a turn within a thermal, where the margin between minimum sink airspeed and stall speed was insufficient to account for turbulence and bank angle.
- Alternatively, the spin may have occurred accidentally during a maneuver to manage altitude for landing.
- Recovery from the spin may have been unsuccessful due to insufficient altitude or improper recovery techniques, noting that the instructor had not operated this specific glider type for over a year.
Safety action
Following the accident, the flying club implemented several safety measures:
- Conducted safety seminars and competency assessments for members, specifically regarding piloting training.
- Prohibited all gliders and powered aircraft from flying over the densely populated residential area near the airfield.