Introduction
On 6 July 1976, at 1534 hours MEZ, a Standard Libelle glider registered as HB-999 was involved in an accident during an off-field landing near Boltigen, Canton Bern, Switzerland. The glider came to rest approximately 200 meters short of the intended landing area after striking a barbed wire fence.
Flight History
The pilot, born in 1923, held a valid glider pilot license and had accumulated 607:53 total flight hours, including 95:57 hours on the accident type. In the preceding 90 days, he had flown 21:39 hours, with 9:01 hours on the type. The flight originated at Zweisimmen airfield at 1124 hours MEZ, with the intention of flying to the Valais region. After releasing from the tow plane northeast of Zweisimmen at about 1800 meters above sea level, the pilot flew over the Spillgerten hills toward Iffigsee and the Sanetsch Pass. Due to rapidly increasing cloud cover, he abandoned the Valais plan and returned toward the Wildstrubel area, reaching approximately 3000 meters. As thunderstorms developed over the Alpine chain, he descended into the lower Simmen Valley. Encountering good updrafts along the Stockhorn chain, he climbed to 2500 meters and then headed toward Thun. Finding no thermals, he returned to the Simmen Valley hoping to regain lift. Over Oberwil and Waldried (about 3.5 to 4.5 km north-northeast of Boltigen), he reportedly gained about 100 meters, reaching 1350 meters. While flying over Oberwil, the pilot inspected a former outlanding field near the railway station where he had landed in 1969. Hoping to find further lift, he continued and was radioed to land at Zweisimmen. The pilot reported his altitude and intention to land at Boltigen.
Accident Sequence
On final approach to a field south of Boltigen, the pilot flew into a headwind and downdraft while rain began. He approached at 120–130 km/h, losing altitude steadily. Approximately 400 meters before the field, a 30-meter-tall building crane was positioned. Unable to clear it, the pilot flew around the crane and barely cleared a high-voltage power line. Shortly after, the glider touched down in wet grass with minimal airspeed about 200 meters short of the intended field, rolled about 8 meters, and at 1534 hours struck a barbed wire fence at coordinates 596.450/164.050, elevation 818 meters.
Injuries and Damage
The pilot sustained serious facial injuries. The glider was damaged, including the canopy, wing leading edge, right wing, and landing gear door. Minor third-party damage occurred to a cattle fence.
Weather Conditions
At the accident site and time, weather reported by the Swiss Meteorological Institute included: flat pressure distribution with thunderstorm tendencies; 3/8–4/8 cumulonimbus base at 2000 meters and 6/8–8/8 altocumulus base at 4000 meters; visibility 15–20 km; wind from SSW to WSW at about 5 knots; temperature 27°C, dewpoint 15°C; QNH 1012 mbar; hazards of rain showers or thunderstorms reducing visibility to about 5 km and gusts to 15 knots.
Probable Cause
The investigation determined the probable cause was a wrong decision during flight and a short landing with collision with an obstacle.