What happened
A non-scheduled IFR flight departed Lille, France, at 12:40 GMT, bound for Wroseb Poland. During the initial climb, the pilot communicated with Brussels ACC, providing progress updates relative to various waypoints including Silly and Gatta. At approximately 12:54 GMT, the pilot reported being at FL 130 and estimated arrival at Olno for 13:10 GMT.
Discrepancies in navigation were noted when the pilot reported passing over Silly for a second time; upon investigation, the radar controller determined the aircraft was actually positioned over Gatta. During this period, the controller was also managing a Caravelle with registration F-BJTQ, which had requested a detour to avoid heavy storms.
By 13:11 GMT, Brussels ACC noted that the Vickers Viscount had failed to provide its expected arrival report for Olno. Subsequent attempts to establish radio contact were unsuccessful, and the aircraft disappeared from radar surveillance. It was later determined that while in cruising flight, the aircraft entered a region of severe weather, lost altitude, and suffered an in-flight disintegration. The aircraft struck the ground at 13:08 GMT. There were four fatalities among the crew.
Findings
Investigators found no specific evidence to explain the sudden loss of cruising altitude. However, the atmospheric conditions near Jeuk were characterized by intense storm activity. It is believed that the aircraft encountered a cumulonimbus cloud, and it is highly probable that severe turbulence caused the pilot to lose control of the aircraft.