What happened
On January 14, 2004, a Socata TB 20 operated by a flight school departed Merville for an instrument flight rules (IFR) training mission. The crew, consisting of an instructor and two student airline pilots, initially performed an instrument approach to Rouen before continuing toward Calais.
While cruising at flight level 50, the instructor identified two cumulonimbus cells near the ABB VOR. Seeking to avoid the cells, the crew requested a trajectory change to pass between them and descended to flight level 40 to avoid potential icing conditions. During this descent, the aircraft entered a region of light turbulence and light precipitation, and the crew lost all external visual references.
At approximately 16:15, the crew witnessed a blue fireball strike the front cowling, accompanied by a loud thunderclap and the smell of burning. While the engine continued to operate, the lightning strike caused widespread electrical failure. The HSI, RMI, second VOR, DME, and heading indicator ceased to function, along with engine parameters, fuel gauges, flap position indicators, and the alternator.
Without navigational aids or visual references, the crew descended rapidly to a safe altitude of 2,200 feet. Once the ground became visible at 2,500 feet, they performed a visual diversion to Le Touquet, where they landed without further incident.
The investigation
The investigation focused on the sequence of events leading to the strike and the aircraft's condition. Investigators examined the weather reports (METAR/TAF) for Rouen, Lille, and Ostend, which indicated convective activity and potential thunderstorms in the region. The investigation also assessed the aircraft's equipment, noting that the F-GGIB was not equipped with weather radar for storm cell detection and was not de-iced.