A powered paraglider is a cheap, cheerful way to take to the skies. But like flying an airplane, a hang glider, or even a drone, it requires the operator to pay attention to every hazard.

On October 30, British twins Hugo and Ross Turner ascended to 8,500 feet in an electric-powered paraglider-like aircraft, called a paramotor. The brothers soared over the ski resort Val d’Isere ...