What happened
On September 7, 1969, during a training camp for the national glider team at the Fricktal-Schupfart airfield, a Standard Libelle glider, registration HB-950, was involved in a ground collision. The event occurred during a training session intended to familiarize pilots with different aircraft types.
As the pilot attempted the first tow flight of the session, the aircraft veered sharply to the left. During the maneuver, the left wing of the glider struck the ground. The aircraft then entered a series of rotations, eventually colliding with another glider, an LS-1 with registration HB-956, which was parked alongside the runway. The aircraft completed a total rotation of approximately 580 degrees around its vertical axis before coming to a halt at the edge of the runway. There were no injuries resulting from the incident, though the HB-956 sustained heavy damage and the HB-950 suffered light damage.
The investigation
The investigation established that the tow plane began its takeoff run on the left side of runway 08, leaving a lateral clearance of only about 3 to 4 meters from the aircraft parked along the runway. At the time of takeoff, a ground assistant was holding the left wingtip of the HB-950.
While the initial start of the takeoff appeared normal, the aircraft's left wing dipped and brushed the ground after the wing walker released the wing. The investigation noted that the aircraft's directional stability was limited at low speeds because the control surfaces were secured with a weight-on-the-spring mechanism. Additionally, the terrain sloping downward in the direction of the veer likely contributed to the loss of control.
During the excursion, the pilot attempted to release the tow rope but could not immediately locate the release handle. The release occurred either through the pilot's manual action or via the automatic safety coupling only after the aircraft had turned approximately 90 degrees from its original heading.
Findings
- The primary cause of the accident was the insufficient lateral distance between the takeoff path and the parked aircraft.
- The pilot's delay in activating the tow rope release contributed to the severity of the excursion.
- The aircraft's reduced directional stability at low speeds, caused by the configuration of the control surfaces, facilitated the leftward veer.
- The downward slope of the ground in the direction of the veer assisted the aircraft's departure from the runway centerline.