Beginning on the night of November 29, 1989 and continuing through April 1990, thousands of residents across eastern Belgium — particularly in the provinces of Liège and Luxembourg — reported a distinctive silent, slow-moving, triangular craft with three white lights at its corners and a red light at its center. The first major wave occurred on that November night, when gendarmes (national police) from multiple jurisdictions independently observed the object, providing extensive written reports within hours. Over the following five months, more than 13,500 written reports were collected by civilian investigators and by the Belgian Air Force.
The case became exceptional because of the response of the Royal Belgian Air Force. On the night of March 30–31, 1990, air-defense radar at Glons (the NATO Ground Control Interception station) detected unknown targets. Two F-16 fighters were scrambled from Beauvechain Air Base. Over the course of roughly seventy-five minutes the jets obtained nine radar locks, each broken within seconds by the objects accelerating away at speeds exceeding Mach 1 and descending at rates that would exceed twenty-five g — far beyond any known aircraft and certainly beyond what any pilot could survive. Extensive data from onboard radar recordings was released publicly by Colonel Wilfried De Brouwer.
A still photograph taken in 1990 near Petit-Rechain by a man named Patrick Maréchal became the iconic image of the wave, showing a black triangle with three corner lights and a central glow. Decades later, Maréchal admitted the photograph was a hoax created with styrofoam; however, the admission applied only to the photograph, not to the many thousands of other reports.
Belgium is the only NATO country to have acknowledged that its air force investigated, engaged, and could not explain a UFO phenomenon. The final official report by the Royal Belgian Air Force concluded that the objects were real but of unknown origin, and it called the case among the most important in the history of military aeronautics.