[AERO EZY] ETREPAGNY (27) 04.01.2015

On 4 January 2015 at 19:45, a passenger on a scheduled flight approaching the outskirts of Paris saw a luminous phenomenon on the ground that appeared to move at the aircraft's speed. Other passengers also saw it after their attention was drawn to it. During a telephone interview, the witness placed the phenomenon to the aircraft's left, at an estimated angle of 50°–70° from the vertical. It sometimes appeared ahead and sometimes behind, occasionally requiring him to turn his head backward. The Moon was 99.6% illuminated, almost due east at azimuth 90.8° and elevation 23.26°, within his field of view. He did not mention it, probably because he was concentrating on the ground. Since the phenomenon seemed to follow the aircraft, GEIPAN immediately favored an optical effect involving a celestial body. It considers specular reflection of moonlight from lakes and flooded areas the very probable cause, making wet areas stand out against the dark ground. The reported filaments were probably flooded paths or small canals. The source cites rain in northern France on 2 and 3 February, despite dating the observation to 4 January; this discrepancy is retained here. The estimated angle of 50°–70° fits the hypothesis: the ideal angle would be complementary to the Moon's approximately 23° elevation, or 67°. GEIPAN attributes the apparent changes between positions ahead and behind the aircraft to changes in heading. The phenomenon would remain due east: directly left of a southbound aircraft, or ahead and left of an aircraft heading southeast. GEIPAN lacked the information needed to correlate the exact flight path with the apparent positions. It classifies the case B: very probable reflections of moonlight from bodies of water and flooded areas.