Air carrier aircraft (in the US) are hit by lightning on the average of about once every 3000 hours.
It has been suggested that aircraft showing symptoms of static electricity (P static on the radio, or St Elmos fire) may be leaving an ionised wake, it is also possible that the jet exhaust leaves a similar wake, even if the aircraft isn't being charged by the environment. This wake acts as a charge path, so aircraft actually
trigger lightning.
If an aircraft is hit, the electricity flows through the airframe, and exits on the other side (the airframe becomes part of the lightning's "circuit").
What can happen if an aircraft is hit? The worst is a
fuel explosion. Jet A is by far the safest fuel to use, it will not normally form a combustible mixture in the tanks at the temperature at which a lighning strike is possible. There has never been a verified lightning caused fuel fire or explosion with an aircraft using Jet A.
Lightning caused fuel explosions have bought down a Pan Am 707 (Dec '63), an Iranian Air Force 747 (May '76), a US Air Force C-130E ('78) an F-4, F-16 and a KC-135, although all of these aircraft were at least partially filled with Jet B (JP-4).
The next worse thing that can happen is
flame out (engine failure). Single flameouts due lightning strikes are fairly common on aircraft with aft mounted engines, dual flameouts have occured, although no accidents seem to have been recorded.
Small
electric shocks have been reported by pilots, but nothing incapacitating.
Beyond this, various types of structural, avionics, electrical and magnatizing
damage is possible. I have pictures of radomes blown apart, wing leading edges peeled back at the rivet line and such. This type of physical damage is usually cased by the sudden heat expansion of air due to arcing within an enclosed part of the aircraft structure, but is fairly rare.
If the aircraft suffers a lightning strike, a post lightning inspection is specified by the manufacturer in the maintenance manuals - which the engineers would carry out before the aircraft took off. In some cases, where the aircraft is at a remote port, an initial inspection can be carried out by the pilot, in order to certify the aircraft safe to fly to an engineering port for a full inspection.
Most of this information can be found in the excellent "Severe Weather Flying" by Dennis Newton.
Have a look here:
www.avweb.com/articles/lightnin.html for a story & pictures of a typical strike in a GA aircraft (an Aerostar).
If you need a (free) password, visit the avweb home page:
www.avweb.com/
[This message has been edited by Checkboard (edited 29 May 1999).]