Accidente del Blanik L-13 durante entrenamiento acrobático en el aeródromo de Schaffhausen con resultado fatal

El 18 de septiembre de 1976, un LET L-13 Blanik estuvo involucrado en un accidente fatal en el aeródromo de Schaffhausen en Suiza. El planeador, pilotado por un instructor y un alumno de acrobacias, perdió el control durante un vuelo de entrenamiento. Testigos informaron de una serie de maniobras acrobáticas seguidas de un descenso en espiral pronunciado. La investigación confirmó una falla mecánica en el enlace de control del alerón derecho, lo que contribuyó a la pérdida de control. Ambos ocupantes murieron y la aeronave fue destruida al impactar.

1. Aerotow aerobatics flight: The instructor and aerobatic student departed Schaffhausen on aerotow for an aerobatic training flight and released near the airfield at about 1000 m above ground.
2. Failed vertical manoeuvre: After several renversements, the pilot pulled the Blanik up to the vertical at about 500 m above ground, where it stopped, slid backwards 50–100 m, and then violently tumbled about the lateral axis.
3. Aileron linkage failure: Around the time the glider returned to normal attitude, witnesses heard a loud bang later determined to be the right aileron control linkage failing, leaving the right aileron inoperative.
4. High control loads: The extreme attitudes and airflow reversal during the botched vertical manoeuvre likely imposed unusually high loads on the flexible aileron control system, contributing to the fracture of the aileron linkage.
5. Attempted recovery actions: After the bang the glider flew straight for about two seconds with flaps and airbrakes partially extended, indicating the crew attempted to regain control and possibly configure for recovery or descent.
6. Uncontrolled right spiral: With the right aileron disabled, the glider entered an increasingly steep, irregular right spiral from about 300 m above ground, with turn rate and speed increasing despite control inputs.
7. Crash - fatal: After 4–5 turns in the steepening right spiral, the glider struck the ground with high speed and about 75–80° right bank, killing both occupants and destroying the aircraft.