Foudre détruit un ASK 21 lors d'un vol d'entraînement près de Northall, Bedfordshire

Le 17 avril 1999, un planeur Schleicher ASK 21 a été frappé par la foudre lors d'un vol d'entraînement près de Northall, Bedfordshire. Le planeur, opérant depuis un site à Dunstable, volait à environ 2 500 pieds lorsque l'incident s'est produit. La frappe de foudre a provoqué la désintégration de la cellule, obligeant les deux occupants à sauter en parachute pour se mettre en sécurité. L'instructeur et l'élève ont tous deux subi des blessures légères, et le planeur a été détruit. L'incident a été observé par plusieurs personnes qui ont rapporté une forte détonation suivie de débris tombant du ciel.

1. Aerotow — thermaling: The ASK 21 was aerotow-launched from Dunstable and spent about an hour soaring up to 4,000 feet between Leighton Buzzard and Bletchley before returning toward the airfield along the edge of an advancing cloud mass.
2. Thunderstorm nearby: A large area of bad weather with heavy rain and wet snow, including cumulonimbus with forecast lightning, was slowly advancing toward the local flying area, with the glider operating close to the cloud edge.
3. Non-conductive structure: The ASK 21’s largely glass-reinforced plastic, non-conductive structure and lack of designed-in lightning protection made it vulnerable to severe structural damage from a lightning strike.
4. Lightning strike: While turning away from the cloud at about 2,500 feet agl, roughly 800 yards from the cloud base and flying at about 80 kt, the glider was struck by a powerful lightning discharge that attached to the airframe.
5. In-flight breakup: The lightning strike caused large sections of the GRP airframe, including most of the right wing, outer left wing, and fuselage center section, to disintegrate and separate in flight.
6. Crew bailout: After an initial dazed period and communication difficulty, the student and then the instructor abandoned the disintegrating glider, with both parachutes inflating by about 1,800 feet agl.
7. Crash - minor injury: The wreckage descended near Northall and was destroyed while both occupants parachuted to the ground with minor injuries, including hearing damage and a broken ankle for the instructor.