I witnessed this accident in which a London Gliding Club K21 was destroyed
in mid-air by what was later found to be an exceptionally powerful lightning
strike. Indeed, the strike was many times more powerful than the most
energetic that commercial aircraft designers typically allow for when
specifying composite components for their aircraft. The pupil, who was a
member of the public on a one day gliding course, parachuted out
successfully, while the instructor suffered minor injuries on landing from
the jump. He was back flying a few weeks later, none the worse for wear, and
continues to fly at the club.

The lightning entered one wing of the glider at roughly the point where the
aileron actuator connects to the aileron, and exited from approximately the
corresponding location on the other wing. The effect was to drive an immense
electrical current though the metal push-rods and other metal fittings in
the fuselage, some of which were vaporised, or else melted and severely
distorted. The effect of this current was to generate a massive amount of
heat which caused the explosive expansion of the air inside the wings. This
stripped the skin off a large part of the wings which, of course, are not
designed to withstand loads that are essentially trying to inflate the wing
from within and peel the skin away from the spar.

The UK Air Accident Investigation Branch took a considerable interest in
this event, not least because a senior investigator happens to be a member
of London Gliding Club and an extremely detailed analysis was published by
them later. This includes a fascinating account of the mechanism of
lightning strikes on aircraft. The UK AAIB report can be found he
http://www.aaib.dft.gov.uk/cms_resou...pdf_500699.pdf. The
accident also attracted the attention of various airlines and aircraft
manufacturers who were interested in the implications for composite
components of commercial airframes.

Contrary to jeplane's quote from Business & Commercial Aviation, the AAIB
report specifically says (in referring to GRP with foam or honeycomb filled
sections bonded together) that "These materials are electrically
non-conductive." Later on it says "In aircraft or gliders constructed from a
non-conducting material such as GRP, the lightning arc is likely to attach
to the extremities of any linked conducting components within that
structure". It was very clear from the AAIB examination of the glider that
it was the electrical conduction through the metal parts, and not through
the skin that caused the aircraft to disintegrate as a result of the events
I have described above.

David Starer

"jeplane" wrote in message
ups.com...
There is an article in this month of "Business & Commercial Aviation"
regarding lightning.

It says that in 1999, a ASK21 desintegrated large sections of the
fuselage, while flying in clear air, about 800 yards from a cloud.
Both pilots were ejected from the strike, but fortunately were wearing
parachutes.

The same article goes on to say fiberglass, especially carbon fiber is
conductive. So if you are on the ground and a thunderstorm is over the
airport, to seek shelter inside a building and NOT inside the glider
which has no protection.

Has nayone heard this before? Do you know someone who had a lightning
strike in a glider before?
I am just curious as I never heard of this before.