Summary
On Saturday, 19 October 1968, at 1410 hours, a Blanik L-13 glider, registration HB-882, crashed on a meadow approximately 3 km north of Schänis airfield in Benken, Switzerland. The glider had been conducting aerobatic training under the supervision of a flight instructor. The pilot sustained serious injuries, and the aircraft was destroyed.
Investigation
The official investigation was carried out by the Swiss Aircraft Accident Investigation Commission, assisted by the St. Gallen cantonal police. The final report was issued on 16 October 1969.
Aircraft
The Blanik L-13 (serial number 173401) was built in 1967 by SPP Kunovice, Czechoslovakia. It was a two-seat, all-metal shoulder-wing glider owned by the Segelfluggruppe Lägern. At the time of the accident, the glider had a total of 481 flight hours and 716 landings. The takeoff weight was 382 kg, within the maximum permissible limit of 500 kg, and the center of gravity was within limits.
Pilot and Instructor
The pilot, born in 1927, held a glider pilot license issued on 19 October 1966 and a passenger endorsement. He began glider training in 1946, resumed in 1965, and started aerobatic training in June 1967. His total flight experience was 87 hours and 39 minutes with 224 landings, including 8 hours and 6 minutes of aerobatic training. He was described as a cautious pilot who tended to make abrupt control inputs.
The supervising flight instructor, born in 1942, held a glider pilot license with aerobatic and instructor endorsements, as well as a private pilot license.
Flight Sequence
On the day of the accident, the pilot conducted three flights. The instructor had assigned a sequence of maneuvers: left spin (two turns), loop, left renversement, left spirals, and a precision landing. During the third flight, the pilot performed a spin, loop, and renversement; the latter was executed with slightly late rudder input, causing a 45° yaw when the nose dropped. After recovery, the pilot flew straight for 1–2 km, then turned right toward the valley at an altitude of 400–500 m above ground.
A witness observed that after completing the aerobatics, the glider flew away in a shallow right turn on a northerly heading. The pilot later stated that during the third flight, he practiced three left spirals. The glider would not recover from the spiral; the control stick was slightly right of center, and he could not move it further right despite using both hands. The glider continued descending in a steep spiral. At about 250 m, he considered bailing out but decided the altitude was insufficient. The airbrakes were partially deployed, and the flaps were asymmetrical (right extended, left retracted).
Damage
The first ground contact was made by the left wingtip. After approximately 9 m, the forward fuselage hit the ground with a nose-down attitude of about 35°, and the glider rotated right and came to rest inverted 33 m from the initial impact. The pilot was seriously injured. The glider was destroyed. Minor third-party damage occurred.
Technical Findings
Post-accident examination revealed that the left flap was retracted and the right flap fully extended. The elevator trim was set to full nose-down. The airbrakes were partially extended. The control system was tested: the left aileron push-pull tube had minor friction from a static discharge cable, but this was easily overcome. The right aileron system showed no binding. The control rods failed due to impact forces. No pre-existing defect was found in the aileron control system. The seat cushions did not cause any control jamming.
Probable Cause
The accident occurred because the pilot failed to recover the glider from a steep spiral for reasons that could not be determined, resulting in ground contact during a left turn.