Expert: Paul Ruderham - 6/25/2009

Question
how does an aircraft manages lightening?

Answer
Hello Sindhuja,
Aircraft, and by that I mean the body of the aircraft and not the occupants inside, are protected from lightning strikes by two things. The first and most important of these is the brains of the pilot and the weathermen who predict where violent storms are likely to be. The second is through a small unsung device called the "static wick".

Most aircraft do not fly into lightning storms, or fly through storms or areas where lightning is likely to be present. What we see as lightning is really a massive flood of electrons seeking equilibrium, either from cloud-cloud or from cloud-ground. In both cases, huge amounts of electric charge build up at the edges of the cloud. The electricity finds it's way from one place to the other via what's called a "step leader".

The sheer power of the cloud will start to attract electrons from the ground. These electrons will gather on anything that gathers charge (like a fence) or sticks up in the air (like a person), or that does both (like a telephone pole). That electric charge will start to work it's way through the air, ionizing it, until the leader working it's way down, and the leader trying to get up finally meet. When they do - there's lightning. An aircraft flying between the highly charged portions of a cloud will act as a conduit for step leaders, being able to produce one in each direction. If either of them meets a leader coming the other way... ZAP.

The way an aircraft tries to dissipate these step leaders is through the use of something called a "static wick". A static wick is a piece of metal connected electrically to the frame of the aircraft, with one or two spikes or needles on the end. It is housed in a fiberglass rod to insulate it from the airplane. Because the spikes concentrate the electric charge around them, and they are connected to the airframe, they allow the airplane to dissipate any static electricity it may build up out into the air. Also - if lightning DOES strike the plane, the chances are that the electricity will go through the dissipator and not through the airplane.

Regards
Paul