What happened
On February 14, 2013, a student pilot was conducting solo flight training at Buttwil airfield (LSZU) in Switzerland. Having recently completed the requirements for a private pilot license, the student was performing maneuvers to prepare for an upcoming practical skill test. The flight consisted of 13 circuits, including complex maneuvers such as engine-out approaches and landings without the use of flaps.
The airfield was covered in snow, with the runway surface prepared to a width of 18.5 meters featuring hard, compacted snow, while the area outside the markings contained deep, soft snow. During the final landing, the Reims Aviation F152, registration HB-CFF, touched down approximately 170 meters past the displaced threshold. While the initial rollout was straight, the aircraft began to drift toward the right. The pilot attempted to correct the deviation using rudder pedals and brakes, but the right main gear eventually entered the deep snow at the edge of the prepared surface. The sudden drag caused the aircraft to pivot sharply, leading to a nose-over that left the aircraft resting upside down in the snow.
The investigation
An investigation by the Swiss Transportation Safety Investigation Board (SUST) examined the aircraft, the pilot's training records, and the airfield conditions. Investigators found no evidence of mechanical failure or technical defects in the HB-CFF. The aircraft's weight and center of gravity were within limits, and all maintenance was up to date.
The investigation also focused on the flight program and supervision. It was noted that the instructor and student had not conducted a formal briefing that morning, as the instructor was occupied with another student on a separate flight. The student had self-imposed a demanding and lengthy training session that lasted over an hour, which investigators believed contributed to fatigue.
Findings
- The primary cause of the accident was the loss of lateral control during the landing rollout on the snow-covered runway.
- The lack of direct supervision by an instructor contributed to the accident, as the flight school's regulations required an instructor to monitor solo circuits.
- The flight program was deemed inappropriate and overly taxing, involving high-intensity maneuvers that led to pilot fatigue and diminished concentration.
- The reduced braking and directional control effectiveness provided by the compacted snow increased the difficulty of maintaining the aircraft on the runway centerline.