Sighting in Tourdun, April 17, 2018

At around 9 p.m., a witness was taking a long-exposure photograph of the sky, with the camera aimed at the zenith between the Big Dipper region (Ursa Major) and Leo. They noticed a streak on the image, which they first took for an ordinary aircraft trail. They also reported seeing the ground light up intermittently in their field of view for about two seconds. Only one witness account was collected.

The investigation identified the star field in the photo using an online star-calibration tool, then worked out the viewing azimuth and the axis of the trajectory. Cross-checking this against aircraft flying over the area identified, with certainty, an Airbus A321 operating the scheduled Munich–Lisbon service (flight LH1792/DLH05A). The white anti-collision lights on its wingtips showed an abnormal sequence: Airbus aircraft normally give two very close flashes at one hertz, whereas the image shows four, or a random pattern. Investigators concluded that the lights were malfunctioning.

When the GEIPAN questioned the witness, they gave a different account: their surprise came from seeing the detail on the photo, and only then did they become aware of the light on the ground. This second version was judged very probably the correct one. It fits a priming effect, in which a first oddity leads a witness to link others to it. The brief nature of the light, seen in peripheral vision, points to a local point source such as car headlights or a flashlight. The case has low consistency: the original photo was not supplied, the angular data had to be reconstructed, and nothing is known about the witness's surroundings. The explanation still stands, and the GEIPAN classified the case as A.