The radar observation of a UFO in Belgian airspace beginning on 3/30/90 and continuing into the early morning hours of 3/31/90 was merely one incident in an extensive period of UFO activity over Belgium and neighboring countries during that year. Observations at Eupen, which were made by citizens and public officials (including uniformed police officers), indicated the presence of a large triangular object which was capable of low altitude / slow speed, hovering, high acceleration, and high speed. In this, the observations were similar to those of nearly a decade before in the Westchester County area of New York state (USA).
A case summary of the Wavre events of 3/30/90 through 3/31/90 indicates that several ground-based radars simultaneously obtained radar signals from the same object at the same time, as judged by the radar operators. At 11:56PM local time, the required conditions for an intercept having been met, two F-16 fighter aircraft of the Belgian Air Force departed their base and attempted to engage the unidentified aircraft. One of the F-16s had a video camera operating which recorded the radar readings and the HUD (Heads Up Display) presented to the pilot. Readings from the HUD display based on the frame rate of the video allowed military analysts to extract information on the performance of the unknown target.
Linear accelerations ranged from 0.5G to 21G.
The largest acceleration occurred at the lowest speed; at higher speeds maximum accelerations were only half of that maximum value.
Turn radii of less than a mile are the rule, despite speeds for some turns in excess of 1000 knots.
Centripetal accelerations range from 8 to 35 G. Combined with linear accelerations, total forces on the UFO structure or occupants would be as high as 50G.
https://web.archive.org/web/20080113151125/http://www.temporaldoorway.com/ufo/analysis/belgianradar/index.htm 
