What happened
On September 12, 2015, a SZD-9 „Bocian” glider departed from Langhennersdorf airfield for a training flight. The flight, conducted via aero-tow, was intended to practice spin recognition and recovery maneuvers. The crew consisted of a flight instructor and an 18-year-old student.
After reaching an altitude of approximately 800 meters and completing circuit patterns, the crew initiated a spin by applying left rudder. During the maneuver, the aircraft entered a prolonged spin that lasted for five to six rotations. The instructor attempted to recover the aircraft by applying right rudder and releasing elevator pressure; however, the aircraft failed to respond to these inputs.
At an altitude of approximately 400 meters, the instructor ordered an emergency egress. The student jettisoned the forward cockpit canopy and unbuckled their harness. As the student attempted to exit, the spinning motion momentarily ceased, but the situation was already too critical to abort the jump. Both occupants exited the aircraft using their automatic rescue parachutes, landing near a local road. The SZD-9 „Bocian” struck a tree in a residential garden, resulting in the destruction of the aircraft.
The investigation
The BFU examined the aircraft's flight data via GPS and inspected the wreckage. The investigation focused on the control surfaces and the aircraft's trim state. While the rear fuselage and tail section were heavily damaged, the investigation found no evidence of mechanical failure in the rudder, elevator, or aileron linkages.
Investigators also reviewed the aircraft's weight and balance. The total weight of the occupants and parachutes was within limits, and the center of gravity was within the permitted range. A key point of interest was the trim setting, as the student reported the instructor had set the aircraft to a tail-heavy trim to accelerate the onset of the stall.
Findings
- The primary cause of the accident was inappropriate control inputs during the recovery phase, which prevented the spin from being terminated in a timely manner.
- The recovery was likely complicated by the aircraft being trimmed in a tail-heavy configuration, which can increase the number of rotations required to exit a spin.
- The instructor's decision to bail out at 400 meters was considered a necessary and appropriate response to the failed recovery attempts.