Flight Details
On 13 July 1975, at 16:30, a pilot departed from Sion Airport aboard a Blanik L-13 glider (registration HB-1049) with his son as a passenger for a pleasure flight. After a tow launch, the glider was released above Chandolin. Using moderate to weak thermals, the pilot climbed via Prabé (2042 m) and Sublage (2374 m) to the foot of Wildhorn (3247 m). From there, he crossed the Rhône Valley straight to Mont Noble (2654 m), reaching an altitude slightly above the summit. When lift ceased, he began descending toward Vernamiège in spirals and turns along the slope.
Accident Sequence
At approximately 18:10, over the Mayens de Vernamiège at an altitude of about 1607 m (approximately 100 m above ground according to a witness), the glider performed two right-hand spirals. A witness reported seeing the glider spiral at low altitude, then disappear behind trees. The passenger stated: "As we finished the second turn of the spiral, the glider went into a steep dive and my father said: 'We're done for!' I don't remember anything after that." The glider struck the ground with the right wing tip, then the nose, and finally the left wing tip after rotating about half a turn to the right. It slid backward 22 m, with the fuselage broken aft of the trailing edge at an angle of approximately 75° to the cabin.
Aircraft Information
The glider was a Blanik L-13, a tandem two-seat, high-wing, all-metal construction, manufactured by LET Kunovice in 1971 (serial number 174 909). It was owned and operated by the Groupement de vol à voile de Sion, Sion. The airworthiness certificate was issued on 10 September 1971, and the registration certificate was valid until 31 March 1980. Total service time was 671.10 hours with 772 landings. Weight and center of gravity were within limits at the time of the accident.
Meteorological Conditions
Weather was influenced by an anticyclone over Europe, providing sunny and warm conditions. At Sion at 16:00, wind was 240° at 8 knots, visibility 25 km, with scattered cumulus at 8000 ft and cirrus at 25000 ft. Temperature was +29°C, dew point +13°C. At 19:00, wind was 240° at 8 knots, visibility 25 km, no clouds. At Vernamiège around 18:00, conditions were: wind light and variable, clear sky, temperature approximately +20°C, light turbulence, QNH 1019 mb, sun azimuth 101° elevation 21°.
Injuries and Damage
The pilot (born 1928) sustained serious injuries; the passenger (born 1960, his son) sustained slight injuries. No fatalities occurred. The glider HB-1049 was destroyed. There was no fire.
Investigation and Probable Cause
The investigation, assisted by the Valais cantonal police, concluded with the final report dated 20 August 1976. No pre-existing defects were found in the glider. The probable cause was stated as: "The accident is due to a stall during maneuvers carried out with insufficient speed margin."