Lightning strike disintegrates ASK 21 alongside thundercloud

Instructor and student of an ASK 21 were lightly injured and the glider destroyed when lightning disintegrated it in flight while soaring near Northall; both bailed out, under canopy by ~550 m AGL. On a training course at Dunstable, it had aerotowed and soared to ~1,220 m for an hour. As bad weather advanced, the instructor turned away from the cloud at ~900 m AGL. 30° clear of the cloud line, at ~760 m AGL and 148 km/h in clear air, a positive discharge over 80 kA struck it. Large airframe sections separated; the instructor broke an ankle on landing. Damage was confined to the aileron system — the only conductive path in the GRP airframe.

1. Training at Dunstable; storms forecast: An ASK 21 was on a training course out of Dunstable, with an instructor and student aboard, both wearing parachutes. A large storm system was advancing slowly from the north.
2. Cruise along advancing cloud front: After a soaring flight up to ~1,220 m, the glider flew along the front edge of an advancing cloud before the instructor turned away to return ahead of the weather.
3. Positive >80 kA strike at 17:08:57 LT: Lightning-detection data recorded a positive strike over 80 kA close to the accident site at the moment of impact — the discharge that struck the glider.
4. Aileron rods crushed; ~1,000°C bolt: Most of the right wing, the outer left wing, and mid-fuselage detached in flight. Lightning current followed the aileron system, melting a bracket bolt and crushing a rod.
5. Both bailed; parachutes open ~550 m AGL: The student bailed out first, followed by the instructor; both parachutes were open by ~550 m AGL. The student landed unhurt; the instructor broke an ankle.
6. GRP gliders have no lightning protection: The ASK 21's GRP structure is non-conductive and has no built-in lightning protection. The strike's current followed the only metallic path — the aileron system.