What happened
On October 23, 1960, a training flight conducted by the Churfirsten Gliding Group at Mollis airfield resulted in an accident involving a Rhönlerche II, registration HB-616. During the flight, which was being conducted by a pilot instructor candidate and a student, weather conditions had significantly deteriorated due to the influence of the Föhn wind.
At approximately 12:38, the aircraft was launched via winch to an altitude of roughly 250 meters. As the pilot attempted to initiate a left-hand approach, the aircraft encountered intense gusts and a strong crosswind from the east. The aircraft's sink rate increased sharply, reaching up to 7 meters per second, while forward airspeed dropped significantly. Realizing that returning to the Mollis airfield was no longer possible, the pilot attempted an emergency landing on a meadow located beyond a railway line. During the maneuver, the right wing of the Rhönlerche II struck a railway power line, causing the aircraft to fall from a height of approximately five meters to the ground.
The investigation
The investigation examined the meteorological conditions, the pilot's experience, and the operational oversight of the training session. Investigators noted that while the pilot instructor candidate possessed good overall flying qualifications, he was relatively inexperienced with the specific local atmospheric conditions present that day. The investigation also looked into the presence of the designated supervising instructor, who was not on-site at the time of the accident.
Findings
- The primary cause of the accident was the decision to continue flight training during unsuitable wind conditions in a mountain valley subject to Föhn winds.
- The atmospheric conditions were characterized by a complex wind structure, where a low-level wind blowing up the valley was part of a larger wind vortex, making the aircraft susceptible to sudden, violent gusts.
- The pilot's lack of familiarity with these specific local weather patterns contributed to the inability to manage the sudden loss of airspeed and increased sink rate.
- The supervising instructor, responsible for overseeing the instructor candidate's practical training, was not present during the flight.
Safety action
While the investigation noted that the pilot's decision to attempt an emergency landing on the meadow was the only viable option under the circumstances, the findings highlight the risks of conducting instructional flights when local weather conditions are known to be unstable and unpredictable.