Sighting in Hyères, May 27, 2016

A witness lying on a beach noticed something odd in the sky, where an aircraft contrail was passing. It was a straight, black or very dark grey shape that the witness compared to a kind of curtain of smoke, running from the ground up into the sky. It did not move, and the witness heard no particular noise. They filmed and photographed it. Theirs was the only account collected during the investigation.

GEIPAN studied the testimony, the photographs and the video. The dark line was explained as a natural phenomenon known as a volumetric shadow seen edge-on (an "edge shadow"). It appears when a straight contrail passes in front of the sun and the sun, the contrail and the observer are lined up. The slice of atmosphere bounded by these three then carries a shadow. That slice acts like a slightly tinted pane of glass: it goes unnoticed when seen face-on, but forms a dark streak when seen from the side. The streak is darker the longer the straight part of the contrail is. As soon as the observer is outside that slice, the streak vanishes. All these conditions were met for the witness, and the streak covered their whole line of sight, sky included. The witness could picture the contrail's shadow cast on the ground, but not a shadow across the sky. GEIPAN therefore classified the case as A: aircraft contrail and a volumetric shadow seen edge-on.