Lightning strike disintegrates ASK 21 alongside thundercloud

The instructor and student of an ASK 21 were lightly injured when lightning disintegrated the glider in flight; both bailed and were under canopy by ~550 m AGL, aircraft destroyed. On a training course at Dunstable, the glider had aerotowed and soared to ~1,220 m for about 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 80 kt in clear air, a positive discharge over 80 kA struck the glider. 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.