On the evening of November 29, 1989, two Belgian gendarmes near Eupen reported a large, low, flat triangle with bright lights underneath. That night 143 people reported similar sightings, though many reports came in after the press got hold of the story.
Sightings went on until April 1990. On the night of March 30 to 31, 1990, radar picked up unknown targets and the Belgian Air Force scrambled two F-16s. The pilots made brief radar locks but saw nothing, and the Air Force later published a report on the night, which is rare for a military.
Skeptics point out that the first sighting fits a helicopter, that the radar contacts may have been weather effects, and that the best-known photo of a triangle, from Petit-Rechain, was admitted as a hoax in 2011. Supporters say this does not explain hundreds of reports.