What happened
On July 19, 2017, a flight instructor and a student pilot were conducting a training flight from Speck-Fehraltorf, Switzerland, in a Jodel D11-2. After completing several successful landings, the crew decided to perform a third circuit. During this final attempt, the aircraft encountered sudden, intense turbulence while turning toward the departure path. Due to shifting wind conditions, the instructor decided to execute a shortened circuit for a landing on runway 12.
During the final approach, severe wind gusts caused the indicated airspeed to fluctuate wildly between 85 km/h and 150 km/h. Realizing the aircraft would not stop within the remaining runway length, the instructor initiated a go-around at full power. As the aircraft turned into the departure path at an altitude of approximately 60 ft, it was struck by a powerful tailwind component. The aircraft lost altitude rapidly, and despite the pilot's efforts to maintain airspeed, the plane entered a steep bank and struck a rapeseed field. The aircraft subsequently flipped and impacted an asphalt road, resulting in two serious injuries and heavy damage to the aircraft.
The investigation
Investigators examined the meteorological conditions, the aircraft's performance, and the crew's actions. The investigation established that a multi-cell thunderstorm system was moving through the region, bringing cold air and gusty winds. While the pilots had monitored the weather and noted darkening skies, the specific turbulence encountered was caused by localized wind shear and air mass movement channeled by the local terrain.
Technical analysis of the Jodel D11-2 showed no mechanical engine failure, but noted that high ambient temperatures (31°C) resulted in a high density altitude of nearly 4,000 ft. This significantly reduced engine power and aerodynamic lift. The investigation also noted that the aircraft's takeoff mass was near its maximum limit, further constraining performance.
Findings
- The primary cause of the accident was a loss of control due to an aerodynamic stall at low altitude.
- The decision to execute the go-around was made too late in the landing sequence.
- The aircraft was flying at a low altitude and insufficient airspeed during the turn.
- Severe turbulence and a strong tailwind component significantly degraded climb performance.
- High density altitude and high aircraft weight limited the available engine power and lift.
- The terrain rising in the direction of flight prevented the pilot from maintaining altitude through level flight.