Décrochage du Ka 4 Rhönlerche II après échec de lancement par treuil sur un aérodrome militaire suisse

Le 21 mars 1964, un Alexander Schleicher Ka 4 Rhönlerche II a subi un échec de lancement par treuil sur un aérodrome militaire en Suisse. Le planeur, piloté par un instructeur de vol et un élève, a subi une rupture de câble pendant l'ascension. Malgré la disponibilité d'une longue piste devant, l'instructeur a tenté de revenir au point de départ. Le planeur a décroché et a vrillé d'environ 15-20 mètres, s'écrasant sur la piste. Les deux occupants sont restés indemnes, mais l'appareil a subi des dommages à l'aile gauche et au nez.

1. Winch launch climb: During a dual-instruction winch launch from a military airfield, the Rhönlerche began its initial climb with the student in front and the instructor in the rear seat.
2. Cable break in climb: After the glider had covered about 200–300 m and reached roughly 50–60 m height, the winch cable’s weak link failed and the cable broke.
3. Adequate landing area ahead: Despite approximately 800 m of hard-surface runway and a further 1000 m of flat grass available straight ahead, the crew did not plan for a straight-ahead landing after the cable break.
4. Student recovers, proposes turn: The student correctly lowered the nose to stabilize the glider after the cable break and then proposed a turn back toward the launch point, which the instructor accepted.
5. Instructor steepens low turn: When the student initiated a left turn that seemed too shallow, the instructor took over and increased the bank angle without increasing airspeed at low altitude.
6. Stall and wing drop: After about 100–120° of heading change, the glider became too slow and stalled, dropping over the left wing from an estimated 15–20 m height.
7. Crash - no injury: The glider struck the hard runway first with the left wingtip and then the nose, sustaining damage to the left wing and forward fuselage, while both occupants remained uninjured.