Impact au sol du Ka 4 Rhönlerche II lors d'un virage à basse altitude à l'aérodrome de Granges
Le 17 avril 1970, un Alexander Schleicher Ka 4 Rhönlerche II a subi un impact au sol à l'aérodrome de Granges, en Suisse. Lors d'un lancement au treuil, l'instructeur a initié un exercice de rupture de câble à environ 70 mètres d'altitude. La réponse tardive de l'élève-pilote a entraîné une perte d'altitude, incitant l'instructeur à prendre le contrôle. En tentant un virage à droite pour éviter un atterrissage en campagne, l'appareil a décroché et a percuté le sol avec son aile droite. Les deux occupants ont subi des blessures légères et le planeur a été gravement endommagé.
- Winch launch climb: During a winch launch at Grenchen, the Rhönlerche II was climbing normally with instructor and student on board.
- Simulated cable break: At about 70 m above ground, the instructor intentionally released the winch cable to conduct a cable-break exercise.
- Delayed pitch response: The student reacted only hesitantly by pushing the stick forward, resulting in inadequate nose-down input and low airspeed.
- 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.
- 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.
- 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.
- 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.