ATHIS-MONS (91) 30.07.2016

On 30 July 2016 at about 7:15 p.m., a witness observed from his car stopped at the red light on the RN7 at Athis-Mons, in the immediate vicinity of Paris-Orly Airport, a luminous phenomenon in the sky on his left as he heads north towards the junction allowing access to the gas station of the nearby shopping centre. The phenomenon is described as a very bright round shape, comparable to a ping-pong ball held at arm's length, appearing stationary for about a minute before moving slowly and then disappearing very quickly in a straight line. The sky is clear and the witness indicates the presence of aircraft in the area during the observation. The position of the witness, located very near the Orly runways, is in an area where approaching aircraft can be observed at a small angle to the line of sight. The analysis of the questionnaire and sketch indicates that the witness was heading north on RN7 and was observing westward to his left, corresponding to the area west of the runways. In this configuration, an aircraft approaching the airport from the west in the radar guidance phase prior to the final alignment may appear almost in the observer's viewing axis. The witness describes an extremely bright object, without visible wings or flashing lights. This description is compatible with the observation of an aircraft seen almost head-on, the powerful landing lights being able to appear as a very bright point in the sky and visually mask the structure of the aircraft from a distance. In this type of configuration, the wings and navigation lights can be difficult to detect, which can give the impression of an isolated circular object. The sequence described by the witness (apparent immobility followed by slow displacement and then very rapid departure) is also compatible with a perspective effect related to the angular velocity of an aircraft observed almost in the axis of its trajectory. When the aircraft approaches along this axis, its apparent motion in the sky may seem very small, giving the impression of a stationary phenomenon. As soon as the angle of observation changes, for example during a slight change of heading or when the aircraft is no longer viewed head-on, the angular movement suddenly becomes greater and can be perceived as a very rapid acceleration. The weather data available for the time of observation indicate a dominant north-west wind of the order of 9-15 km/h. Although this wind direction generally leads to the use of west-facing runways (runway 25), wind speed remains relatively low and the operating configuration of an airport can be maintained or modified for operational reasons. Under these conditions, the use of an east-facing approach (runway 06), involving aircraft arriving from the west, remains compatible with observed weather conditions. Given the immediate proximity of Orly Airport, the geometry of the observation, the light characteristics described and the well-known perceptual effects associated with the observation of an aircraft seen almost in the axis of its trajectory, the observed phenomenon appears to be compatible with the landing lights of an aircraft in the approach phase towards the airport. The most plausible hypothesis for the observation is therefore that of an aircraft approaching the Paris-Orly arrival circuit, whose landing lights were perceived as an intense light point, giving the witness the impression of a stationary circular object and then moving away quickly. However, it was not possible, due to the lack of radar data available for analysis, to identify the aircraft accurately. GEIPAN notes that the area immediately surrounding Orly Airport is under constant aviation safety surveillance, and that a UAP sighting there would have been logged as an anomaly. GEIPAN classifies this observation case as "B": likely observation of an aircraft approaching Paris-Orly airport whose landing lights were observed almost in the axis of trajectory.