What is being depicted in the image is known as a “Vortex Ring State”. This type of turbulence in dangerous for helicopters because of the downdraft created by the ring, this can cause a rapid descent of the aircraft. In order to recover, the pilot performs the “Vuichard Recovery Technique”, and moves toward the updraft of the vortex ring. In combination with some other maneuvers, the helicopter will eventually stabilize.

The image is seeded by an aerosol and you can see the torus beginning to form.

Photo Credit: Richard Chapuis / Air-Glaciers

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