Behind the Forecast: The striking interaction between lightning and planes

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Science Behind the Forecast 3/1/19

LOUISVILLE, KY (WAVE) - Each year the Federal Aviation Administration (FAA) watches over more than 15,800,000 flights. That boils down to around 43,000 flights every day! In the U.S., there are around 100,000 thunderstorms each year. Many of flights are struck by lightning; on average, each airplane in the United States’ commercial fleet is struck by lightning more than once every year. So why don’t we hear about more damage to aircraft?

Lightning is the massive discharge of electricity between the atmosphere and the ground or within the atmosphere itself. Negative and positive charges between two locations increase until they overcome the insulative nature of the air resulting in a release of electricity, or lightning. Lightning can be intra-cloud (within a cumulonimbus cloud) or cloud-to-ground; sometimes lightning even shoots up towards space. Lightning can strike more than 10 miles away from the source storm. Positive cloud-to-ground lightning strikes can have a charge of 1 billion volts.

Florida airport ground worker struck by lightning

This airport worker amazingly survived a lightning strike as he worked on the tarmac at a Florida airport. He has now been released from the hospital after being treated for third degree burns.

Posted by NBC News on Wednesday, August 2, 2017

The FAA has regulations in place to make sure that aircraft are protected from harm. Typically, jet aircraft can safely fly over thunderstorms as long as their flight altitude is above the cloud tops, according to the FAA. If a route is impeded by significant weather, air traffic is rerouted, reduced or a ground stop is implemented. “Pilots definitely try to avoid lightning. Anything with that much power is not something to be messed with,” pilot Ken Hoke stated. “But if we do get hit, it’s not something we worry about. After we land, we let the maintenance technician know we had a possible lightning strike and he will give the aircraft a close look.” An aviation meteorologist’s job revolves around informing pilots about dangerous weather and helping to create safe flight plans in order to keep planes away from hazardous conditions.

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Here’s the thing. Much the lightning that strikes aircraft each year is actually triggered by the plane itself! According to studies, the strike begins at the aircraft as it travels through a very charged portion of a cloud then stretches away in opposite directions. At first, lightning attaches at the aircraft’s nose or the tip of a wing, according to the Scientific American. The plane then flies through the flash which re-attaches on the fuselage as the aircraft remains part of the electrical circuit. The electrical current streaks through the aircraft’s exterior before exiting out of an extremity.

“Most lightning we see are just bright flashes with no thunder that can be heard from inside the aircraft. If the lightning occurs very close to (or strikes) the aircraft, we see the flash and hear the boom simultaneously. It's tremendously bright and loud,” Hoke said.

Most aircraft now have conductive skin made of aluminum. However, more modern planes are constructed with compositive materials that are embedded with fibers or screens to make them more conductive. Engineers must make sure that there are no gaps in the conductive path on the exterior of the airplane to avoid issues within. Of course, an aircraft’s skin near fuel tanks must be quite thick with fasteners designed to avoid sparks. Lightning diverter strips are placed on the surface of a plane’s radar to protect it; radar does not work within a conductive enclosure, according to the Scientific American.

“The aircraft exterior receives very minor damage,” Hoke explained. “At the lightning entry point (usually near the nose) maintenance personnel will find 4 or 5 very small holes in the aircraft skin (about the size of a toothpick). The holes are often conveniently located where rivets are already installed. When the lightning detaches at the rear of the aircraft, it often leaves several more small toothpick-size holes in the skin. The holes are completely harmless. They are so small that they do not effect the pressurization system or structural integrity of the air frame. The holes are easily and quickly repaired with rivets.”

Because of work to improve the structure of airplanes, a commercial flight has not crashed because of a confirmed lightning strike since December 8, 1963. On this date, a Pan American Boeing 707 was struck by lightning over Elkton, Maryland killing all 81 people onboard. According to investigators, the lightning strike ignited jet fuel vapor in a wing tank causing it to explode.

While damage to the aircraft is rare nowadays, momentary blindness from flashes has been reported by some pilots. However, many take steps to prevent that situation from occurring. “When we are flying at night through an area with lightning potential, we turn on all the interior cockpit lights - full brightness,” Hoke explained. “This reduces the chance of us being temporarily blinded by a nearby lightning flash.”

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