What happens when an aircraft is struck by lightning?

Aircraft are struck by lightning far more often than you might think. Fortunately, while one might expect a fatal outcome, they are designed so that this poses no risk.

Every day, several aircraft are struck by lightning. If most of the time this is without consequence, it’s because they’re designed to cope with such events, which doesn’t mean they don’t need to be inspected after the event, as it remains a potentially dangerous phenomenon that could require major repairs depending on the intensity and context of the event, or if the context is unfavorable. Which hardly ever happens.

What is lightning?

Let’s start at the beginning.

Lightning is a natural phenomenon of high-intensity electrostatic discharge that occurs in the atmosphere, between electrically charged regions, and can occur either within a cloud, between several clouds, or between a cloud and the ground.

A single flash can contain up to 1 million volts or 30,000 amperes.

What is the probability of an aircraft being struck by lightning?

According to the various figures we found, a given aircraft is struck by lightning once or twice a year, or approximately every 1,000 flight hours.

These figures need to be nuanced, as they depend on a number of factors.

The first is the use of aircraft. Of course, an aircraft that flies little is less likely to be struck by lightning than one that flies a lot, but that’s not all.

In fact, there are certain phases of flight when an aircraft is more likely to be struck by lightning: the ascent and descent phases. Indeed, the figures show that the risk of lightning strikes is greatest between 2,000 and 15,000 feet (a commercial aircraft generally flies at 33,000 feet and above).

Source : Boeing

So an aircraft that takes off and lands several times a day, even over short distances that mean it can’t fly high, is more likely to be struck by lightning than one that operates one or two flights a day.

Then there’s the geographical area of operation. Lightning is synonymous with thunderstorms, and while thunderstorms can occur anywhere in the world, there are parts of the globe where they are much more frequent. Mainly the areas around the equator, but not only.

On the map below, the orange, red and black zones are those that recorded the highest number of lightning flashes.

Source: Meteo Suisse

In short, a medium-haul aircraft operating several rotations a day in the Caribbean is statistically more likely to be struck by lightning than a long-haul aircraft operating between Helsinki and Tokyo.

What happens when lightning strikes an aircraft?

The lightning will strike the aircraft at a protuberance (nose, wingtips) and follow the path of least resistance along the fuselage, which acts as a Faraday cage, protecting passengers (like the bodywork of a car) until it reaches an exit point.

Source : Boeing

Instead of saying that the aircraft is struck by lightning, we’ll say that it travels along the fuselage. It’s just a waypoint encountered on its way to the ground. So if it has found an entry point, all you have to do is lead it to an exit point, and it’s back on course for the ground.

Aircraft are therefore specially designed to conduct and dissipate lightning. This is what the rods you see along the wings are for, for example. We can say that the path taken by lightning striking an aircraft is “under control” thanks to the aircraft’s design.

Similarly, there are safeguards to prevent sensitive electronic equipment from being affected.

A problem arises, however, with the most modern aircraft, such as the Boeing 787 or Airbus A350, where certain parts are made of composite materials or carbon, materials that conduct electricity much less well than metal. This is a problem because the aim is to conduct lightning away from the aircraft, not conserve it.

These aircraft are therefore fitted with special protection features and layers of conductive material in composite parts.

What are the effects of lightning on an aircraft?

As already mentioned, sensitive electronic equipment and electrical circuits are specially insulated so as not to be affected by lightning, even though pilots sometimes report instruments flickering for a few seconds.

Similarly, the tanks are insulated so that no sparks can come into contact with the fuel.

Boeing notes, however, that a strike of unusually high intensity can damage components such as electrically operated fuel valves, generators, power supplies and electrical distribution systems. This has never actually been observed, but is physically possible.

Much less serious than the effect sometimes caused on observers, passengers and crews, who sometimes see a flash of lightning and hear a loud “bang“. But it’s also not uncommon for the crew to be unaware that the aircraft has been struck by lightning.

As a result, minor damage can be found on the ground (burn marks, small holes, damaged sensors) without the crew even realizing it.

Is lightning really dangerous for aircraft?

A figure is worth more than any explanation. In 2021, only 11 lightning incidents were reported, i.e. after being struck by lightning, pilots felt unable to continue flying under normal conditions. That may sound like a lot, but out of 304 million flights, it’s not much.

The last commercial aircraft accident directly attributable to lightning occurred in 1963. Pan Am Flight 214 crashed near Elkton, Maryland, on a flight from San Juan, Puerto Rico, on its final leg from Washington, D.C. to Baltimore. All 81 passengers and crew were killed in the accident.

It was in the wake of this tragedy that the FAA mandated the use of lightning rods on all commercial aircraft flying in U.S. airspace.

Finally, lightning is especially dangerous for people outside the aircraft. In 2021, a Vietnam Airlines technician tragically died after being struck by lightning while doing maintenance on an aircraft on the ground.

Bottom line

While lightning is a common event for aircraft, they are designed to have little or no consequences, and they conduct lightning more than they suffer from it.

Image : aircraft struck by lightning by Sergey Nivens via Shutterstock

Bertrand Duperrin
Bertrand Duperrinhttp://www.duperrin.com
Compulsive traveler, present in the French #avgeek community since the late 2000s and passionate about (long) travel since his youth, Bertrand Duperrin co-founded Travel Guys with Olivier Delestre in March 2015.
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