What happened
On May 15, 1976, a Standard Libelle glider, registration HB-973, was returning from a competition flight at Birrfeld airfield. While flying near Thalheim at an altitude of approximately 1,000 meters, the pilot experienced a sudden and significant loss of altitude. Realizing the intended airfield was no longer reachable, the pilot sought an alternative landing site in an open field near Schinznach Dorf.
To assess the landing area, the pilot performed several turns. During the approach, the pilot encountered further turbulence and increased sink rates. Attempting to manage the descent, the pilot initiated a 90-degree right turn at approximately 90 km/h. However, as the sink rate increased to about 5 m/s, the pilot accelerated and immediately began a second right turn. During this maneuver, the right wing struck a main road and a parallel fence. The aircraft then clipped a tree with the left wing before the fuselage made contact with the ground. The glider slid 90 degrees away from the intended landing direction and struck another tree, which caused the right wing to break.
The investigation
The investigation established that the pilot was properly licensed and had sufficient flight experience, including previous experience with off-field landings. The aircraft was properly registered, and its weight and center of gravity were within limits. Weather conditions at the time consisted of clear visibility and light winds, but the terrain and atmospheric conditions presented challenges.
Findings
- The pilot encountered unexpected downdrafts during the approach to the emergency landing site.
- The loss of altitude and increased sink rate forced the pilot to initiate flight maneuvers earlier than planned.
- The available altitude and airspeed reserves were insufficient to complete the approach as intended, leading to the wing striking obstacles.
- The investigation noted that pilots participating in competitions may face increased pressure to reach the primary airfield.