What happened
On April 17, 2007, an FFA AS202/15-1 aircraft, registered as HB-HFI, departed Lausanne-La Blécherette for a planned navigation training flight toward St. Gallen-Altenrhein. The flight was being conducted under visual flight rules (VFR) by a student pilot and an instructor.
During the flight, the crew entered the rear Neckertal valley. Approximately four kilometers before reaching the end of the valley, the aircraft performed a 180-degree turn to head back toward the valley exit, followed by another 180-degree turn that directed the aircraft back up the valley. While executing a left-hand turn, the aircraft struck the terrain at an altitude of approximately 3,606 feet AMSL. The impact resulted in two fatalities and the total destruction of the aircraft.
The investigation
Investigators examined the flight path, cockpit instruments, and local topography to reconstruct the sequence of events. Analysis of the terrain revealed that while the valley appeared relatively open from the west, the southern slope becomes significantly steeper just two kilometers before the crash site.
Technical examinations of the HB-HFI showed no evidence of mechanical failure or pre-existing technical defects. The aircraft's weight and balance were within limits, and the engine and instruments were functional. The investigation also reviewed the crew's experience and the environmental conditions, noting that the weather was clear with nearly calm winds at the time of the accident.
Findings
Determining the cause of the accident, investigators concluded that the aircraft collided with the ground because the crew maintained an altitude that provided insufficient clearance for a safe turnaround or for crossing the lowest surrounding ridges within the narrow valley basin.
Several contributing factors were identified:
- Inadequate local topographical knowledge regarding the narrowing of the valley and the steepening of the slopes.
- Delayed intervention by the flight instructor during the maneuver.
- The terrain constraints at the time of the turn left very little lateral space, as the aircraft was likely drawn toward the center of the valley to avoid the steep, forested slopes, further reducing the available width for a safe 180-degree turn.