Flight Details
On 28 July 1975, a glider L-13 Blanik, registration HB-995, operated by the Segelfluggruppe Rigi, was involved in an accident on the west slope of Unterer Schafberg, Graubünden, Switzerland. The pilot, born in 1933, held a glider pilot license with passenger and instrument flight endorsements and had accumulated 1,237:38 flight hours, including 38:25 hours on type. The passenger, born in 1958, was a student pilot with 11:38 hours of flight experience.
The pilot and his daughter departed from Samedan for a winch launch at 14:00. After release at about 400 m above ground, they flew to Muottas Muragl, gaining altitude. After approximately one hour, at around 2500 m above sea level, they attempted to cross to the Schafberg area. A witness flying nearby observed the glider at a distance of 200 to 250 m and about 100 m lower, performing a full circle near the slope. The glider entered a steep turn with high bank angle, and during the second rotation, it struck the slope at an estimated angle of 50°. Another ground witness reported that the glider flew along the slope, turned right toward the slope, banked, and after completing two circles, impacted the ground. The passenger stated that the Fowler flaps were half extended and the airspeed was about 80 km/h before the glider suddenly yawed to the right. The pilot retracted the flaps, but the glider impacted after 0.5 to 1.5 turns. The accident occurred at 15:01 at coordinates 789'350 / 153'400, elevation 2340 m.
Investigation Findings
Examination of the wreckage revealed no pre-impact technical malfunctions. The glider's weight (approximately 470 kg) and center of gravity (0.166 m) were within permissible limits. The right Fowler flap was fully extended, the left about 2/3 extended; the right airbrake was about 1/4 open, left about 1/2 open; the landing gear was extended. The airspeed indicator was jammed at 38 km/h, with a red mark at 70 km/h. The trim lever was set to "SINKT" (nose down). The flap control in the rear seat was in the "OFF" position but not locked, and the airbrake lever was 2/3 extended. The pilot's autopsy determined that death resulted from impact injuries; toxicology was negative. The passenger survived due to energy absorption by the fuselage structure and rapid rescue by helicopter.
Probable Cause
The probable cause of the accident is falling below minimum airspeed near the slope, with contributing factors of inappropriate flight tactics and misoperation of the Fowler flaps.