Summary
On Wednesday, 8 August 1962, at approximately 1812 local time, a Grunau Baby II glider (registration HB-565) collided with the wooded west slope of Girshubel near Zweisimmen, Switzerland. The pilot, a student pilot, was uninjured, but the glider sustained heavy damage. The subsequent investigation concluded that the accident was probably caused by a stall in diminishing updraft.
Investigation
The investigation was conducted by the Swiss Federal Aircraft Accident Investigation Commission. The wreckage was examined at the accident site, and the fuselage remained intact while both wings had broken near the strut attachments. A defect was found in the rudder control system: the locking screw for the upper rudder hinge fitting was missing, allowing the fitting to rotate. However, tests showed that the rudder could still be moved freely through its full range of motion without noticeable resistance, and the defect likely did not significantly affect controllability.
Aircraft and Pilot
The glider was a Grunau Baby II, a single-seat, high-wing wooden training glider built in 1951. It was owned by Segelfluggruppe Oberaargau, Langenthal. The maximum takeoff weight was 250 kg, and the weight at the time of the accident was about 250 kg, with the center of gravity within limits. The glider had accumulated 438 total flight hours, with 22 hours since its last official inspection on 2 April 1962.
The pilot, born in 1937, held a student pilot license for motor and glider aircraft valid until 25 March 1963. He began glider training in April 1961 and had a total flight experience of about 8 hours in 45 flights, with about 2 hours in 16 flights on the accident type. His longest flights were 45 minutes dual and 16 minutes solo. No previous accidents or violations were recorded.
Accident Sequence
The flight took place during a glider camp at Zweisimmen. On 6 August, the pilot had flown a familiarization flight with an instructor. On 8 August, he first flew two solo circuits and a 16-minute hill attempt. Then, at 1420, he started a towed flight without a time limit set by the instructor. After about 10 minutes, he released at about 1500 m altitude and found wave lift. He spent nearly three hours in smooth wave updraft, reaching about 3300 m. As evening approached, the wave diminished. Around 1800, near St. Stephan, he was about 800 m above the valley floor and intended to land but first sought to gain altitude.
At the steep, wooded west slope of Girshubel, he encountered weak lift (0.2 m/s). He flew back and forth along the slope. According to his statements, during a right turn away from the slope at 65 km/h, he had difficulty initiating the turn and needed excessive bank. After that, he flew at a 35-45° angle towards the slope, then tried to initiate a left turn away but felt the rudder barely moved and the aircraft responded only to ailerons. Approaching the slope, he pulled back on the control stick. At 1812, after a 3-hour 50-minute flight, the glider flew into trees.
Damage and Findings
The pilot was uninjured. The glider was heavily damaged: the fuselage was intact, but both wings broke near the strut attachments. The recovery team noted that the locking screw for the upper rudder hinge fitting was missing. Detailed examination indicated the fitting had likely been rotated for some time. Tests showed that even with the rotated fitting, the rudder pedals could be moved to stops without noticeable resistance, and the rudder could be fully deflected without deformation. The defect did not significantly impair control. The only other damage was minor tree damage.
Probable Cause
The investigation concluded that the accident was probably due to the student pilot stalling the glider in diminishing updraft near the slope, possibly aggravated by his limited flight experience and fatigue from the nearly four-hour flight.