Glider collision with unmarked cable in French Alps leads to injuries

Casualties unknown • Dingy-Saint-Clair, FR

A STEMME S-10V glider struck an unmarked lift cable near Parmelan mountain, resulting in a flat spin and a crash into a tree-covered slope.

What happened

On 5 August 2020, a STEMME S-10V self-launching glider, registered F-CAOT, was conducting a local flight near the Chambéry - Challes-les-Eaux aerodrome. The pilot, accompanied by one passenger, had been utilizing local thermals before flying north toward Lake Annecy and the Lachat mountain area.

While returning along the southern rock face of the Parmelan summit, the glider's left wing struck a lift cable. The impact caused the aircraft to become unstable and enter a flat spin. The glider subsequently collided with a tree-covered mountain slope. Both the pilot and the passenger sustained injuries, and the glider was destroyed.

The investigation

The BEA investigation utilized FLARM data and the pilot's statement to reconstruct the flight path. The investigation established that the pilot was relatively unfamiliar with the region, having arrived the previous day, and was following another glider during the flight. Although the pilot was using a 2020 gliding map that indicated the cable, he did not observe the obstacle during the outbound leg or the return leg.

Investigators examined the status of the cable's visibility. While the cable, which reaches a height of approximately 120 m, was originally equipped with markings, these had deteriorated over time. Following a 2010 determination by the French Civil Aviation Safety Directorate (DSAC-CE) that additional marking hardware might pose a hazard, the owner had removed the markings. While the cable was listed in the aeronautical information service as an "unmarked cable," the investigation noted that the FLARM obstacle database was not updated with this specific information at the time of the accident.

Findings

  • The pilot was flying at a lower altitude on the return leg, positioned below the ridgeline and closer to the cliff wall, which likely prevented him from seeing the refuge or the pylon that would have alerted him to the cable's presence.
  • The lack of a cable marking system contributed to the pilot's failure to detect the obstacle.
  • The collision with the cable was the direct cause of the loss of control and the subsequent spin.

Probable cause

The accident was caused by the glider striking an unmarked lift cable, a collision made more likely by the absence of physical markings on the cable and the pilot's inability to visually identify the obstacle while flying close to the terrain.

Frequently asked questions

What happened in the 2020-08-05 STEMME S-10V accident near Dingy-Saint-Clair, FR?

A STEMME S-10V glider struck an unmarked lift cable near Parmelan mountain, resulting in a flat spin and a crash into a tree-covered slope.

What aircraft was involved and where did it happen?

The accident on 2020-08-05 involved a STEMME S-10V, registration F-CAOT, at Dingy-Saint-Clair, FR.

What was the probable cause of the accident?

The accident was caused by the glider striking an unmarked lift cable, a collision made more likely by the absence of physical markings on the cable and the pilot's inability to visually identify the obstacle while flying close to the terrain.

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