Sighting in Émerainville, August 4, 2017

Between 1:55 and 2:10 p.m., a witness noticed an object in the sky at roughly the altitude of airliners at cruising height. Through binoculars, they saw it hanging motionless: a vertical cylinder, red-orange on its upper third and white on the lower two thirds. A large cloud coming from the southwest then hid it. During this time, two aircraft passed almost directly overhead, one travelling west to east and the other from the southeast toward the northwest. When the cloud cleared, the object was gone. The witness thought of a drone, while noting that the object was at a high altitude. No other witness came forward.

According to the GEIPAN, what struck the witness as strange was the object's apparent stillness, its shape and its disappearance. Yet stillness is hard to judge: the cloud may have covered the object because the object itself was moving toward it, at least in part. An airliner seen from far away often looks like a wingless cylinder or cigar, because sunlight reflects steadily off the rounded fuselage, whereas reflections off the wings are stronger but very brief. The cylinder's apparent verticality is a subjective impression that depends on the aircraft's orientation relative to the line of sight. An aircraft with no contrail can also become invisible when its reflection changes, and it is then impossible to find again with binoculars. The witness was also in an area of heavy air traffic, and an earlier sighting they had reported to the GEIPAN arose from the same context.

Analysis of the aeronautical context showed nothing unusual in the observation itself. The GEIPAN therefore did not try to identify the specific aircraft, since the aircraft explanation was so probable, and classified the case as A: aircraft.