Incident Overview
On 20 April 1974, a Standard Libelle glider registered as HB-950 was involved in an accident near Weesen, Switzerland. The aircraft was participating in a training camp for the Swiss national gliding team at Schänis. The pilot, born in 1924, held a valid glider pilot license with 3,000 total flight hours, including 1,100 hours on the accident type. No health issues were noted at the time of the accident.
Flight History
The scheduled flight was a 248 km triangular course from Schänis to Sonthofen to Klosters and back to Schänis. Before takeoff, pilots were briefed on meteorological conditions, including expected downdrafts in the final approach area. The pilot departed in HB-950, and the flight proceeded normally until the final phase. Approximately 60 km from Schänis, the pilot initiated the final approach with an estimated height reserve of 400 m.
Accident Sequence
Over the western half of Lake Walen, HB-950 encountered widespread downdrafts with speeds up to 6 m/s, causing a significant altitude loss. Unable to reach the destination airfield, the pilot decided to perform an off-field landing near Süstli. During the landing approach, with the sun low on the horizon and in backlight conditions, the glider collided with a 16 kV overhead power line. The left wing severed the earth wire suspended above the two main conductors at a height of approximately 25 m above ground. The resulting deceleration rotated the aircraft about 46° to the left. Subsequently, the right wing struck a 380 V line running parallel to the Linth river and the intended landing direction. This impact rotated the glider back toward the landing direction. The right wing broke three of the four wires of the 380 V line and became entangled on the fourth, while the left wing struck the ground and fractured inboard of the aileron. The glider came to rest at 1710 hours MEZ in a 70° left bank, with the fuselage suspended horizontally about 4 m above the ground. The dangling earth wire caused a short circuit, de-energizing the lines. The pilot reported the accident by radio to Schänis and then exited the glider using a ladder.
Damage
The pilot was uninjured. The glider sustained severe damage. Minor third-party damage occurred.
Investigation Findings
- The pilot had a valid license and adequate experience; no evidence of impairment.
- No technical defects were found on the glider. Weight and balance were within limits.
- The chosen landing field was located in an area crossed by several power lines. The 16 kV line was not marked on the terrain nor indicated on obstacle charts.
- Weather at the time: wind weak from west to north at about 5 kt, visibility 10–20 km, 3/8 to 5/8 cirrus and cirrostratus clouds, temperature 14°C, sun azimuth 264° and elevation 21°.
- The low sun likely blinded the pilot during the approach, preventing him from seeing the power line.
Probable Cause
The probable cause of the accident was a collision with a high-voltage line during a forced landing attempt due to sun glare.