What Would Happen if Lightning Struck Your Airplane?

December 4, 2015 | Joanne Kennell

Photo credit: Robert Körner/flickr (CC BY-NC-SA 2.0)

Passenger films lightning while in flight.

It is quite unforgettable when you witness lightning from the safety of your home, but imagine flying through a large storm and seeing lightning right outside your window. Would you be scared?

A few days ago, a passenger on a flight entering Brisbane, Australia captured footage of a large storm producing lightning streaks across the sky, terrifying the passengers.  This storm was so intense, it generated at least 28,000 lightning strikes in a single evening.

Were the passengers’ fears justified?  To answer that question, it is important to first understand what lightning is and how it forms.

Have you heard of Benjamin Franklin? Well, the renowned inventor and politician wanted to prove that lightning is a form of electricity so he proposed flying a kite with a metal key in a thunderstorm (whether or not he actually conducted this experiment is unclear). According to legend, when Franklin reached for the key after the storm, he received a shock, proving his idea that lightning is static electricity.

For lightning to occur, there must be a separation of positive and negative charges, with negative charges lower in the cloud and positive chargers above and on the ground.  This allows electric fields to form and grow not only within the cloud, but also between the cloud and the ground.  

Diagram illustrating the distribution of positive and negative chargers during a lightning storm. Negative: lower clouds. Positive: upper clouds and ground.
Photo credit: Environment Canada

There are two main lightning types: Cloud-to-ground (CG), and cloud-to-cloud (CC).  CG is the most dangerous and destructive form of lightning, but CC is the most common.  For CG lightning to form, negative charges within the cloud make a path toward the ground — called a stepped leader.

Since opposite charges attract, positive charges on the ground respond by moving upward from the ground. These are called upward leaders.

When the stepped leader and upward leader meet, 30 to 100 meters above the ground,  negative charges flow downward, and almost instantaneously, a current shoots up to the cloud which follows the path of the stepped leader.  This is known as the return stroke, and it is what we see as lightning. The typical lightning we see actually travels from the ground to the cloud, not the other way around!

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CG lightning either carriers negative or positive charge, meaning there is either a net transfer of negative or positive charge from the cloud to the ground.  Negative strikes are the most common, making up 95 percent of all CG strikes.  Positive charges on the other hand, although very rare, carry a higher charge because the strikes originate from high up within the cloud.  Positive lightning strikes tend to cause more damage, and are associated with power outages and fires.

So can any of these forms of lightning bring down an airplane?  The short answer is, it shouldn’t.  When an airplane gets hit by lightning, the current will travel through the plane’s outer metal shell before harmlessly exiting at some other point.  Modern airplanes are made from lightweight carbon composite that is covered with a thin layer of copper — which makes the airplane act as a Faraday Cage — meaning that the space inside the metal (i.e. passengers) are protected from electric currents.

The sight of lightning outside your airplane window may still make you nervous, however, you should remember that airplanes are specifically designed to withstand lightning strikes.  There is a good chance you have already been on an airplane that was struck by lightning — you just didn’t know it.

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