Accident Details
On 17 April 1970 at 0849 hours, a Rhönlerche II glider registered as HB-589 commenced a winch launch from Grenchen airfield. At approximately 0850 hours, during a turn executed close to the ground, the aircraft's right wingtip contacted the terrain, followed by a hard impact. The two occupants—a flight instructor and a student pilot—sustained light injuries and were treated on an outpatient basis. The glider suffered serious damage, with no third-party damage reported.
Investigation Findings
Both the instructor and student held valid licenses, and no health impairments were identified. Meteorological conditions were deemed irrelevant to the accident sequence. The glider had been properly maintained and was certified for operation. The center of gravity (CG) was measured at 0.530 meters behind the reference plane, which, while near the rear limit, remained within the approved range (0.365–0.540 meters).
The investigation revealed that the instructor initiated a simulated cable break exercise, releasing the winch cable at an altitude of approximately 70 meters. The student reacted slowly, applying forward elevator pressure only after a delay. Following the instructor's directive to veer left, the student began a left turn with insufficient airspeed and using only the rudder. This resulted in a rapid loss of altitude. The instructor then took control, first pushing the nose down to regain speed, then initiating a right turn at treetop height to avoid an off-field landing. The turn was flown with a steep bank. As the instructor attempted to level the aircraft near the ground, it responded poorly to control inputs, likely due to a stalled aerodynamic condition. The rearward CG position may have contributed to a tendency to pitch up, exacerbating the stall. Subsequently, the right wingtip struck the ground, and the glider impacted hard while rotating approximately 180 degrees.
Conclusion
The accident was attributed to the aircraft entering a stalled condition during a low-altitude turn, causing the right wing to contact the ground and resulting in a hard impact.