Accidente del LET L-13 Blanik durante entrenamiento de acrobacias en el aeródromo de Schaffhausen

El 18 de septiembre de 1976, un LET L-13 Blanik se estrelló durante un vuelo de entrenamiento de acrobacias en el aeródromo de Schaffhausen en Suiza. El instructor de vuelo y un estudiante realizaban maniobras cuando la aeronave perdió el control tras una falla mecánica del alerón derecho. El planeador entró en una espiral pronunciada y se impactó contra el suelo a alta velocidad, resultando en la destrucción de la aeronave y la muerte de ambos ocupantes. La investigación confirmó la falla mecánica como un factor contribuyente a la pérdida de 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.