Impacto en tierra del Ka 4 Rhönlerche II durante un giro a baja altitud en el aeródromo de Grenchen

El 17 de abril de 1970, un Alexander Schleicher Ka 4 Rhönlerche II sufrió un impacto en tierra en el aeródromo de Grenchen, Suiza. Durante un lanzamiento con cabrestante, el instructor inició un ejercicio de rotura de cable a aproximadamente 70 metros de altitud. La respuesta tardía del alumno piloto provocó una pérdida de altitud, lo que llevó al instructor a tomar el control. Al intentar un giro a la derecha para evitar un aterrizaje en campo, la aeronave entró en pérdida y golpeó el suelo con su ala derecha. Ambos ocupantes sufrieron heridas leves y el planeador quedó gravemente dañado.

1. Winch launch climb: During a winch launch at Grenchen, the Rhönlerche II was climbing normally with instructor and student on board.
2. Simulated cable break: At about 70 m above ground, the instructor intentionally released the winch cable to conduct a cable-break exercise.
3. Delayed pitch response: The student reacted only hesitantly by pushing the stick forward, resulting in inadequate nose-down input and low airspeed.
4. Low-speed left turn: Following the instructor’s command to head slightly left, the student initiated a left turn using only rudder at insufficient speed, causing rapid height loss.
5. Instructor’s low turnback: The instructor took over, pushed strongly to regain speed, then in tree-top height initiated a steep right turnback to avoid an off-airfield landing.
6. Stall in steep turn: In the steep low-altitude turn with an aft center of gravity, the glider entered an over‑stalled condition and responded poorly to control inputs.
7. Crash - minor injury: The right wingtip struck the ground and the glider impacted hard, rotating about 180° on its yaw axis, causing serious airframe damage and minor injuries to both occupants.