Summary
On 25 April 1970, a K 8 B glider (HB-764) was seriously damaged during an off-field landing near Langnau am Albis, Switzerland. The pilot was performing a training flight and had to land after losing altitude in a downdraft. The glider struck a tree and a wire fence. The pilot was not injured.
Pilot Information
The pilot, born in 1942, held a valid glider pilot license issued on 16 September 1964. He began glider training on 12 July 1960. Total flying experience: 42 hours 50 minutes and 170 launches, with 13 hours 32 minutes and 16 launches on the accident type. On the accident day, after a seven-month break, he completed two dual-control flights on a Rhönlerche (11 and 5 minutes). He had no previous incidents.
Aircraft Information
The glider was a K 8 B (serial 8281/1964), single-seat, shoulder-wing, mixed construction (steel tube fuselage, wooden wing). It was owned by Sportfluggruppe des Personals der Swissair. Maximum permissible weight: 308 kg; weight at time of accident: approximately 280 kg. The certificate of airworthiness was valid until 31 March 1971.
Terrain and Weather
The accident occurred on the east slope of the Albiskette at Langnau am Albis, 5 km north of Hausen am Albis airfield. The selected landing field, 240 m long with an 8% gradient, was bordered on the east by a 1.2 m high wire fence and 4-8 m high fruit trees, and on the west by a road. Weather: 7/8 cloud cover, cumulus base at 1800 m, visibility 40 km. Wind at 500 m: 240°, 10-15 kts, gusts 20-25 kts. Turbulence moderate to strong near slopes.
Accident Sequence
The flight began at 13:14 local time with an aerotow from Hausen am Albis. The pilot released the towline at Albishorn after 4-5 minutes, reaching 1200 m above the airfield. He followed other gliders to the lee side of the Albiskette, encountering updrafts up to 5 m/s. He flew to the Horgen area on the left shore of Lake Zurich, then along the Sihl valley to Üetliberg, where he regained 1100-1200 m. On the return flight along the Sihl valley, he encountered a downdraft and could not reach the windward side. Over Langenberg near Langnau am Albis, he decided to land on a field at the western exit of the village. He executed a 90° right turn to the west and approached with spoilers retracted in a shallow descent. Shortly before reaching the field, a wind shift caused a sudden loss of altitude. The left wingtip struck the outer branch of a 5 m high apple tree at about 3.5 m above ground. The glider then impacted a wire fence, yawed left about 100°, and came to rest with a broken left wing and compressed fuselage about 10 m beyond the fence.
Damage
The pilot was uninjured. The glider sustained severe damage (approx. 50% of its value). Minor third-party damage occurred.
Discussion and Conclusion
The pilot held a valid license, and no health issues were found. The glider was airworthy with no pre-existing defects. Weight and center of gravity were within limits. The off-field landing became necessary because the pilot, with insufficient altitude reserve, was on the lee side and encountered a downdraft. The selected field was suitable, but the landing failed because the remaining altitude was not enough for a steep approach appropriate for the wind conditions. The accident was attributed to inappropriate flight tactics.