LET L-13 Blanik crash during acrobatics training at Schaffhausen airfield

On September 18, 1976, a LET L-13 Blanik crashed during an acrobatics training flight at Schaffhausen airfield in Switzerland. The flight instructor and a student were performing maneuvers when the aircraft lost control after a mechanical failure of the right aileron. The glider entered a steep spiral and impacted the ground at high speed, resulting in the destruction of the aircraft and the fatalities of both occupants. The investigation confirmed the mechanical failure as a contributing factor to the loss of control.

1. Aerotow acro flight: During an aerobatic training flight after aerotow release at about 1000 m AGL near Schaffhausen, the instructor and student began performing maneuvers in the Blanik L-13.
2. Vertical climb and tail slide: From about 500 m AGL the glider was pulled up into a vertical attitude, then stopped and slid backwards 50–100 m, gaining speed and then violently tumbling about the lateral axis.
3. Structural control failure: Shortly after recovering to normal attitude, witnesses heard a loud bang associated with a change at the wings, later found to be a fracture in the right aileron control linkage that rendered the right aileron ineffective.
4. Abnormal control inputs: During the abnormal tail‑slide and tumble, large or uncoordinated aileron inputs and high aerodynamic loads likely overstressed the already flexible aileron control system, contributing to the linkage failure.
5. Unrecoverable right spiral: With the right aileron failed, the glider flew straight briefly then entered an increasingly steep right spiral with large bank angle and growing speed from about 300 m AGL, with no effective recovery despite flap and airbrake deployment.
6. Crash - fatal: After 4–5 steep spiral turns the Blanik impacted the ground with high speed and approximately 75–80° right bank, destroying the glider and fatally injuring both occupants.