Accident du Ka 4 Rhönlerche II lors d'un vol d'entraînement à l'aérodrome d'Olten
Le 23 mai 1970, un vol d'entraînement impliquant un Alexander Schleicher Ka 4 Rhönlerche II à l'aérodrome d'Olten en Suisse s'est terminé par un accident. Le planeur, piloté par un instructeur avec un élève, a subi un décrochage lors d'un virage à basse altitude après une rupture de câble simulée. L'instructeur a tenté de récupérer l'appareil, mais celui-ci a percuté le sol avant de terminer la manœuvre. L'élève a subi des blessures légères, tandis que l'instructeur est resté indemne. Le planeur a subi des dommages importants, et il y a eu des dommages mineurs à des tiers.
- Aerotow initial climb: The instructor and student began an aerotow training flight from grass runway 23 at Olten airfield and climbed out normally behind the towplane.
- Low-altitude simulated break: As briefed, the instructor released the tow rope at about 15 m above ground near the end of the runway to simulate a cable break.
- Very low height: The simulated cable break and subsequent maneuver were initiated at only about 15 m above ground, leaving minimal height margin for turns or recovery.
- Obstacle proximity: Trees located roughly 120 m south of the departure path reduced lateral obstacle clearance and pressured the instructor to fly a very tight turn.
- Tight low turn initiated: The instructor took control, banked right slightly, then began a left turn back with bank increasing to about 50° or more to tighten the turn away from the trees.
- Stall in steep turn: During the steep, low-altitude turn the glider apparently dropped below minimum speed, became sluggish to control inputs, and stalled before the instructor could level the wings.
- Crash - minor injury: Still in a partially banked attitude with a shallow nose-down flight path, the glider struck the ground before completing the turn, heavily damaging the aircraft and causing minor injury to the student.