What happened
On July 26, 2012, an Alisport Silent 2 Targa, registration HB-5522, was engaged in a VFR flight from Grenchen toward the Alps. After climbing to approximately 3,000 meters near Ste-Croix, the pilot began a glide toward the Romont region. During this phase, the aircraft's ground speed averaged 143 km/ and was significantly higher than the aircraft's best glide speed of 90 km/h.
As the aircraft approached the Le Gibloux area, the altitude continued to decrease. While flying northeast of Romont, the pilot attempted to deploy the retractable engine system. However, the deployment occurred at an extremely low altitude—approximately 240 meters above ground—and at a distance of only three kilometers from the intended landing site. Eyewitnesses observed the aircraft performing a left turn at an altitude of just 30 to 50 meters before the nose dipped, causing the aircraft to strike a field at a 30-degree angle. The impact resulted in one fatality and the total destruction of the aircraft.
The investigation
SUST examined the flight path, meteorological conditions, and technical state of the aircraft. The investigation utilized FLARM data and radio communications to reconstruct the sequence of events. Investigators noted that the pilot had recently participated in a flight with an experienced competition pilot, where tactical considerations for crossing the Mittelland were discussed.
Technical analysis of the aircraft revealed that the retractable engine had only partially deployed, reaching an angle of approximately 45 degrees relative to the longitudinal axis. Evidence suggested that an insufficient battery charge prevented the full extension of the mechanism. Furthermore, the investigation confirmed that the pilot's flight speed during the glide phase was roughly 60% higher than the optimal glide speed, which led to a much lower arrival altitude than planned.
Findings
- The pilot's high-speed glide approach caused the aircraft to arrive in the Romont region roughly 400 meters lower than if the best glide speed had been maintained.
- The decision to deploy the retractable engine was made too late, well below the recommended safety margin of 500 meters above a potential landing field.
- The delayed decision to deploy the retractable engine left insufficient time and altitude to manage the complex task of engine startup and landing preparation.
- The engine mechanism failed to fully extend due to a likely low battery state, creating an immediate need for an emergency landing.
- The combination of high-pressure decision-making, low altitude, and the mechanical failure of the engine deployment led to the loss of control.