Collision du Ka 4 Rhönlerche II lors d'un atterrissage en campagne d'entraînement à l'aérodrome de Winterthur

Le 24 mai 1969, un Ka 4 Rhönlerche II a été impliqué dans un incident à l'aérodrome de Winterthur, Suisse. Lors d'un vol d'entraînement, l'instructeur et l'élève pilote ont dû effectuer un atterrissage en campagne en raison d'une altitude insuffisante. L'appareil est entré en collision avec une machine agricole stationnaire lors de l'atterrissage. Les deux pilotes sont indemnes, mais le planeur a subi des dommages importants. Le rapport officiel attribue l'incident à une erreur de jugement de l'instructeur lors de l'approche d'atterrissage.

1. Aerotow training flight: Instructor and student departed Winterthur on an aerotow in a Rhönlerche II for an instructional flight and released at about 500 m AGL near Wiesendangen.
2. Weak unusable thermals: After release the instructor attempted to use weak thermals near Wiesendangen but was unable to gain or maintain sufficient altitude.
3. Low height on return: The instructor instructed the student to return to the airfield at about 300 m AGL, and the circuit was flown down to roughly 120 m AGL, leaving limited height margin.
4. Too low for airfield: During the student’s turn onto base leg at about 30 m AGL with a strong headwind and a 4 m gravel heap on the approach path, the instructor recognized that the airfield could no longer be reached safely.
5. Decision to outland: The instructor decided to perform an outlanding in the field below and executed a strong right sideslip to lose height and align for landing.
6. Obstacle not avoided: Wind drift during the right sideslip and reduced field visibility from the rear seat contributed to the glider’s path bringing the left wing close to a stationary hay tedder near the field edge.
7. Outlanding - damage: After a normal touchdown and 2–3 m of ground roll in the field west of the airfield, the left wing struck the parked agricultural machine, heavily damaging the glider but leaving both pilots uninjured.