What happened
On June 26, 2020, a pilot was conducting a solo training flight in a Schempp-Hirth Arcus T, registration HB-2496, at Birrfeld Airport (LSZF). The flight was part of a transition training program. While the pilot had previously completed two dual flights with an instructor, this session was intended to be a solo circuit following a tow start.
During the tow start, the aircraft encountered intense turbulence and heavy gusts. The pilot, following advice from the tow pilot, disconnected from the winch at approximately 380 meters above ground level. Due to strong northwesterly winds, the pilot performed a shortened approach pattern, turning into the base leg earlier than usual. During the final approach, the aircraft maintained an average airspeed of approximately 135 km/ to h.
In an attempt to configure the aircraft for landing, the pilot accidentally deployed the camber flaps to the "L" position instead of the spoilers/air brakes. This error, combined with high speed, caused the aircraft to bounce several times on the grass runway. The glider continued traveling at approximately 85 km/h, overrunning the end of the runway and crossing a cantonal road at a height of only about 5 meters. The aircraft eventually came to a stop in a nearby field. There were no injuries to the pilot or any third parties, and the aircraft sustained no damage.
The investigation
The SUST investigation examined the meteorological conditions, the pilot's actions, and the aircraft configuration. Investigators analyzed radar imagery from MeteoSchweiz, which showed thunderstorm cells passing north of Basel and south of Lucerne. While no precipitation was recorded directly at the airfield, the investigation established that outflow from these cells created significant wind gusts, reaching up to 30 knots at the airfield.
Findings
- The pilot was under significant stress due to sudden weather changes, which led to the incorrect manipulation of the camber flaps instead of the air brakes.
- The pilot's decision-making was influenced by the visual interpretation of radar imagery on a smartphone, which showed no precipitation over the airfield, potentially masking the risk of the approaching gust front.
- The high approach speed and the failure to deploy air brakes resulted in a landing that was too long, leading to the runway excursion.
- The investigation noted a persistent safety deficit regarding the proximity of public roads to the runway ends at Birrfeld, as the aircraft's path nearly intersected with vehicular traffic.
Safety action
The investigation noted that MeteoSchweiz is considering improvements to weather apps, such as adding wind/gust maps or warnings to radar imagery, to help pilots better identify outflow risks. The SUST also highlighted the ongoing risk to third parties in the airfield vicinity, noting that previous safety recommendations regarding runway end protection have not yet resulted in concrete mitigation measures.