Sighting in Émerainville, June 5, 2017

Between 11:58 and 12:03, under a clear sky, a witness noticed a phenomenon in the sky that puzzled them. To the north-west, at medium height, they saw two lights side by side, like the beams of two headlights. Behind them they could make out a sort of cylindrical fuselage. The whole thing moved horizontally eastward at about the speed of an aircraft and at low altitude. It then stopped and appeared to hover, before climbing almost vertically. A commercial airliner at medium altitude, coming from the north-east, seemed to cross its original path. The airliner kept its course, while the object resumed its horizontal flight on its original heading. It seemed to stop a second time, then climbed almost vertically again until it vanished completely from the witness's view. The witness thought it was an unknown craft disturbed in its course by the airliner, and asked the GEIPAN to investigate. They were the only person to report it. They also gave the wrong year, 2015, in their free-text account.

The air traffic record showed the witness was in a busy area, at least at that hour, with aircraft at all altitudes, including light aircraft making low-altitude circuits. An aircraft at low or medium altitude can be recognised by its lights, which may be on in daytime, and by its body. At low altitude it can carry out all kinds of manoeuvres, such as training manoeuvres: slowing down, changing heading, which a witness may read as a sharp drop in speed when the aircraft goes from crossing the line of sight to flying along it, or sudden changes of altitude. Hovering and a vertical climb are hard to judge from the ground, and the witness themselves used the words "it seems" and "almost". Since the observation itself contained nothing strange, the GEIPAN did not investigate the scenario the witness had imagined. The sighting took place in broad daylight in an urban area, so a genuine anomaly would hardly have gone unnoticed by the many potential witnesses on the ground and in the air. The same witness submitted a similar report two months later. The GEIPAN classified the case as A: aircraft.