What happens when a plane is hit by lightning

asks Pathfinder:
A. It's estimated that most commercial planes are lightly struck by lightning at least once a year.

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Q. Why so frequently
A. Bigger commercial planes can trigger lightning by simply flying through a heavily charged region of cloud. When this happens, the lightning flash begins at the plane and extends away in opposite directions.

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Smaller planes are thought to be struck less frequently because of their size and because they often avoid stormy weather.

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Q. Can lightning knock a plane out of the sky
A. The last commercial plane crash directly attributed to lightning occurred in the US in 1967. The lightning caused the fuel tank to explode. Today's planes use modern techniques to protect against lighting - each plane has to go through painstaking lightning certification tests.

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Q. So what happens if a plane is struck
A. The passengers might see a flash and hear the loud rumble of thunder. If the lightning strikes the plane, it will attach to an extremity such as the nose or wing tip. As the plane flies through the lightning flash, it becomes attached to other parts of the fuselage. The current travels through the conductive outer covering - made mostly of aluminium, which conducts electricity well. The lightning leaves via some other extremity, such as the tail. By making sure that there are no gaps in the path of the lightning, it can be kept safely on the exterior of the plane.

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Q. What if the plane is not made of aluminium
A. Sometimes very modern planes are made of composite materials, which are far less conductive than aluminium. They have a layer of conductive fibres embedded in the skin to deal with lightning currents.

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Q. Does the lightning affect anything on the plane
A. It may cause lights to flicker or interfere with instruments for a few moments. Dozens of small onboard computers are often susceptible to disturbance from power surges. So the aircraft design must ensure that no surges from the lightning reaches them by using shielding, grounding and surge suppression devices.

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Q. What about the fuel tank
A. The outer skin around the fuel tanks is made extra thick so it can't be burned through. Everything connected to the fuel tank - access doors, fuel caps, vents, pipes and fuel lines, as well as the engines themselves - are protected against lightning.

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By Sheena Miller

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