Accident Details
On 21 March 1964 at 1403 local time, a Rhönlerche II glider, registration HB-702, departed from a military airfield for a dual-control training flight using an auto-win launch. The aircraft was owned by the Nidwalden Section of the Aero-Club of Switzerland and operated by the Nidwalden Gliding Group based in Stans. The instructor, born in 1939, held a glider pilot license since August 1958 and a glider instructor endorsement since September 1963, with 182 gliding hours and 664 launches. He had not flown since 24 November 1963 and resumed training that day with a 5-minute solo flight before the accident flight. The student, born in 1930, held a student license issued on 8 May 1963.
During the climb, the winch cable and its drag chute began rotating continuously. When the glider had traveled approximately 200–300 meters and reached an altitude of about 50–60 meters, the weak link in the cable broke. The instructor, judging the student's proficiency sufficient, allowed the student to continue handling the controls. The student correctly pushed the nose down and stabilized the flight. When the student suggested a turn to return to the start point, the instructor agreed, despite the availability of about 800 meters of paved runway ahead followed by about 1000 meters of level grass.
The student initiated a left turn. The instructor found the bank angle too shallow, so he took over and increased the bank without increasing airspeed. After a heading change of about 100–120 degrees, the airspeed became too low, and the glider stalled at about 15–20 meters above the ground, dropping the left wing. The aircraft struck the paved surface first with the left wingtip and then with the nose, coming to rest damaged.
Damage and Injuries
The two occupants were uninjured. The glider sustained damage to the left wing and the forward fuselage. Estimated repair costs were approximately 2500 Swiss Francs, representing about 25% of the aircraft's value.
Investigation Findings
The investigation determined that the cable rotation during the launch was likely due to asymmetry in the drag chute, which caused the weak link to fail under twisting loads. This created a classic launch failure scenario: the aircraft at low altitude in the takeoff direction, requiring a straight-ahead landing. The attempt to return to the start point with a turn (often called an "emergency turn") is a known risk, as low-altitude turning can easily lead to speed loss and stall. In this case, the instructor, whose rear-seat view was somewhat restricted, misjudged the altitude when deciding to turn back. With at least 700–800 meters of paved runway remaining straight ahead, followed by about 1 kilometer of level grass, a straight-ahead landing would have posed no significant risk. The decision to turn may have been influenced by a desire to avoid a long walk back to the start point with the glider.
Conclusion
The accident occurred because, after a cable break during a winch launch, the glider instructor attempted to return to the start point with a turnback maneuver. The available height was insufficient, causing the glider to lose airspeed during the turn and stall, resulting in a wing-drop and collision with the ground.