What happened
On July 31, 2017, a Piper PA28, registration F-GHBA, was conducting a general aviation flight from Turin, Italy, to Lyon Bron, France. The aircraft was carrying two pilots and two passengers. After departing Turin, the pilot climbed toward the ALPIGNANO waypoint, following the highway toward Susa. Upon encountering a cloud layer near Susa at approximately 5,500 ft, the crew decided to descend to 5,000 ft to remain below the cloud base.
After passing Susa, the aircraft turned north into a valley leading toward the Mont Cenis pass. Due to the valley's "S" shape, the crew lost visual contact with the pass and eventually found themselves facing the Mont Cenis dam. Realizing they were flying too low to clear the terrain, the pilot handed control to the more experienced co-pilot to execute a left-hand turn. During this maneuver, the aircraft's stall warning activated, and the plane entered a stall, striking trees and impacting the ground. The impact triggered a fire; while the two passengers and the co-pilot managed to escape the wreckage before the fire spread, the pilot in the left seat had to be rescued by emergency services after the flames were contained.
The investigation
The BEA examined the wreckage, which was located in a steep, wooded, and damp area below the dam. The investigation focused on the pilots' flight preparation, the meteorological conditions, and the navigation charts used. Investigators noted that the flight plan had been updated to an earlier departure to avoid worsening weather, but the specific route through the valleys under the ridgelines had not been studied or prepared. The investigation also reviewed the pilots' experience levels and the limitations of the VFR charts used, which did not provide detailed topographic information regarding the heights of the dam or the Mont Cenis pass.
Findings
- The crew decided to descend into a valley without having prepared for the specific terrain or obstacles encountered.
- The pilots were distracted by a discussion regarding whether they were in the correct valley, which caused them to ignore warnings from a passenger about their low altitude.
- The decision to fly into an unprepared mountainous area under the ridgelines led to the emergency situation.
- The narrowness of the valley made a safe U-turn impossible given the aircraft's performance and altitude.
- The VFR charts used lacked sufficient detail for navigating valleys under ridgelines, as they did not indicate the altitude of the dam or the pass.
- A dilution of command authority occurred because the decision-making process became shared between the two pilots due to the difference in their experience levels.