What happened
On 18 June 2021, a Flight Design CTLS-ELA, registration F-HVAT, was conducting a cross-country instructional flight from Annecy-Meythet to Chambéry - Challes-les-Eaux. The crew, consisting of an instructor and a student-pilot, landed at Chambéry at 18:56 and departed again at 19:00, intending to return via the Bauges Mountains.
Shortly after departure, the aircraft performed a full left-hand turn near Thoiry, likely an attempt to gain altitude before entering the valley. The aircraft then proceeded at a low altitude through the center of the valley toward the Col des Prés pass. Witnesses observed the aircraft flying at a height of only several tens of meters above the trees. While navigating the valley, the aircraft attempted a right-hand turn-around. During this maneuver, the right wing struck trees, causing the aircraft to impact the ground and catch fire. The impact resulted in two fatalities.
The investigation
The BEA investigation examined the wreckage, flight data, and meteorological conditions. Investigators found that the aircraft was operating near its maximum permissible weight. Meteorological analysis revealed that while visibility was good, the day was characterized by high temperatures (a yellow heatwave warning was in effect) and a southwesterly wind. These conditions likely created downdrafts on the eastern slope of the terrain.
Analysis of the aircraft's history showed that while the instructor was highly experienced in multi-engine jet aircraft, his recent experience in light, single-engine piston aircraft and specific mountain flying was minimal. The investigation also noted that the aircraft's engine performance would have been reduced due to the high density altitude and high ambient temperatures.
Findings
The investigation established that the accident was caused by an attempted turn-around before flying over a pass, which led to the collision with terrain. Contributing factors included:
- An insufficient altitude margin when entering the valley, which prevented the crew from safely clearing the pass.
- An underestimation of how high temperatures, altitude, and high aircraft weight would negatively impact climb performance.
- The decision to fly in the center of the valley, which restricted maneuvering space and exposed the aircraft to potential downdrafts.
- A lack of recent mountain flying experience and specific experience in the aircraft type by the instructor.
- Inadequate flight preparation regarding the complexities of navigating via natural references in mountainous terrain for a student-pilot's first cross-country flight.
Safety action
Following the accident, the flight training organization implemented new safety measures, including a prohibition on solo flights in mountainous areas for students and the establishment of prohibited flying zones within mountain ranges for the ATO.