Fatal mountain collision involving Robin DR400-140B

Casualties unknown • Col du Pas de la Coche, Belledonne Massif, FR

A flight in the Belledonne Massif ended in a fatal terrain collision after the pilot entered a valley at an altitude lower than the pass, likely exacerbated by carbon monoxide exposure.

What happened

On 12 September 2020, a Robin DR40/140B, registered F-GSBS, departed Grenoble Le Versoud aerodrome for a local flight. The pilot, accompanied by two passengers, intended to fly toward Chamrousse by traversing the Pas de la Coche pass and following the eastern slope of the Belledonne Massif.

After completing a 360-degree turn, the aircraft entered the valley leading to the pass at an altitude of 6,150 ft. However, the aircraft's altitude dropped to 6,400 ft at the valley floor, which was lower than the pass itself. During the flight, the aircraft's ground speed and vertical climb rate decreased significantly. The aircraft eventually collided with the terrain approximately 100 meters below the pass, resulting in a post-impact fire. The crash resulted in three fatalities.

The investigation

The BEA examined the wreckage and flight path data, which was recorded via a private radar application. Investigators found that the aircraft likely struck the ground with a slight nose-down attitude during a left turn. While the engine appeared to be producing power at the time of impact, a detailed inspection of the exhaust system revealed a crack in the outlet pipe caused by corrosion.

Toxicological analysis of the occupants revealed high levels of carbon monoxide (CO) in the blood of both the pilot (26%) and the passengers (13%). The investigation also noted that the pilot had not received specific training in mountain flying and had a limited amount of recent flight experience. Furthermore, the flight was being conducted as a private arrangement for BIA students and was not officially authorized by the flying club's management.

Findings

  • The pilot entered a valley at an altitude lower than the ridge line and the pass.
  • The aircraft transitioned to the backside of the power curve, leading to a loss of control during an attempted turn-around.
  • Carbon monoxide poisoning likely impaired the pilot's decision-making and ability to monitor flight parameters.
  • The pilot lacked specific knowledge regarding the unique challenges of mountain flying, such as the loss of a natural horizon and restricted maneuvering space.
  • The presence of power lines in the valley prevented a safe turn-around maneuver.

Probable cause

The accident was caused by the pilot's transition to the backside of the power curve and subsequent loss of control during a turn, likely driven by a lack of mountain flying expertise and exacerbated by CO-induced physiological impairment.

Frequently asked questions

What happened in the 2020-09-12 ROBIN - DR400 - 140B accident near Col du Pas de la Coche, Belledonne Massif, FR?

A flight in the Belledonne Massif ended in a fatal terrain collision after the pilot entered a valley at an altitude lower than the pass, likely exacerbated by carbon monoxide exposure.

What aircraft was involved and where did it happen?

The accident on 2020-09-12 involved a ROBIN - DR400 - 140B, registration F-GSBS, at Col du Pas de la Coche, Belledonne Massif, FR.

What was the probable cause of the accident?

The accident was caused by the pilot's transition to the backside of the power curve and subsequent loss of control during a turn, likely driven by a lack of mountain flying expertise and exacerbated by CO-induced physiological impairment.

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