What happened
On May 21, 2020, a pilot attempted a takeoff from the Speck-Fehraltorf airfield (LSZK) in a Stemme AG S10-VT, registration HB-2515. During pre-flight inspections, the pilot noted uneven grass heights on the grass runway, specifically observing that the area to the right of runway 30 contained taller vegetation. To avoid this, the pilot intended to offset the aircraft's takeoff roll slightly to the left of the runway centerline.
As the motor glider accelerated, reaching approximately 50 km/m after a distance of 150 meters, the right wingtip struck the tall grass. This impact caused the aircraft to enter a spin, resulting in the aircraft rolling backward through the grass until it came to a stop. The aircraft sustained heavy damage, including a detached vertical stabilizer and damaged landing gear. One person on the ground was slightly injured during the event, while the pilot escaped the wreckage uninjured.
The investigation
The investigation examined the runway configuration and the vegetation management practices at the airfield. While the operational width of the grass runway is 18 meters, the available safety area (clearance zone) extends to 25 meters. The investigation found that the airfield management had utilized a permitted flexibility to shift the runway axis to reduce wear on the turf. However, this shift resulted in the right-hand boundary of the runway being positioned directly against unmanaged meadowland.
Investigators also reviewed biodiversity guidelines from the Federal Office of Civil Aviation (FOCA), which encourage later mowing to support local ecology. While these guidelines allow for higher vegetation in certain areas, the investigation noted that excessive height can create safety risks for light aircraft.
Findings
- The Stemme AG S10-VT has a wingspan of 23 meters, leaving only a 2-meter margin within the 25-meter wide clearance zone.
- The vegetation on the right side of the runway reached a height of approximately 80 cm, significantly exceeding the recommended limits for light aviation safety.
- The collision with tall grass caused the sudden loss of directional control and the subsequent spin.
- The pilot's attempt to maintain a leftward offset was complicated by the difficulty of visually aligning the aircraft's axis when the runway centerline is shifted and lacks clear structural symmetry.