Lightning is a powerful force, one seemingly capable of great destruction in the right circumstances. It announces itself with a searing flash, followed by a deep rumble heard for miles around.

Intuitively, it might seem like a lightning strike would be disastrous for something like a plane flying at altitude. And yet, while damage is possible, more often than not—a plane will get through a lightning storm unscathed. Let’s explore the physics at play.

Flying High

According to organizations in the know, like the National Weather Service and Airbus, in-service commercial passenger planes get hit by lightning one to two times a year on average. Despite this, crashes due to lightning strikes are extremely rare in these aircraft. One might imagine that a modern airliner, full of complex electrical systems and fuel, would be highly sensitive to a large release of electrical energy. However, thanks to basic physics and smart design, modern commercial planes are actually able to weather a lightning strike quite well.

Much this comes down to the way electrical current flows through a conductor. In a traditional airliner with an aluminium fuselage and wings, the outer body of the aircraft acts as a Faraday cage. This sees the current from a lightning strike flow primarily through the exterior of the aircraft, without harming anything inside. The lightning strike typically contacts the outside of the aircraft at one point, and leaves the aircraft at another, while the electronic systems inside are largely undisturbed. This effect also works in composite-bodied aircraft, thanks to aircraft manufacturers including conductive foils or strips in the fuselage to ensure this effect is preserved. “All components of the aircraft structure (metallic or composite) must be bonded together with bonding leads or with fasteners to ensure electrical continuity,” notes Airbus in a discussion on the topic. “This will enable the lightning current to travel through the aircraft structure without creating significant damage.” Those onboard the plane might here a loud noise and see a giant flash, but actual impact to the aircraft’s structure and electronic hardware is usually very limited.

It’s worth noting that this protective effect is quite important, because aircraft themselves have a tendency to attract lightning when flying through an area of strong electrical field. As explained by Airbus, lightning leaders projecting from a storm can readily meet up with lightning leaders emanating from a plane’s wings, nosecone, tailplane, or other extremities. When this happens, the plane, effectively a large conductor, becomes part of the lightning channel when the discharge happens, carrying current as part of the lightning’s path. A lightning strike may enter the plane at the nose, with discharge passing from the tail, wingtips, or other pointed protrusion. Static discharge wicks can help in this regard. These are small pointed metal protrusions fitted across an airliner’s body, which are intended to release static electricity built up from friction with the air, dust, or precipitation during flight. They can act as discharge points for a lightning strike, too.

While modern aircraft are designed to survive lightning strikes, it’s still better to not get hit in the first place. Often, damage is minor or inconsequential, but planes still need to be checked over after a strike event regardless. For that reason, pilots rely on weather forecasts and guidance from air traffic control to fly around or over danger areas wherever possible.

In the event a modern airliner is struck, damage usually fits the description you’d expect from a large arcing event. Metal components may show burn marks, holes, or pitting, along with deformation from excess heat. Composite parts may also show fiber damage, delamination, or damage to conductive elements impacted by the strike. Post-strike inspections are thus performed to find and repair this damage before a plane flies again.

Unfortunately, while damage or crashes due to lightning strikes are rare, they do still occasionally happen. Flightline Flight 101 crashed in 2001, with the small turboprop plane suspected to have gone down due to electrical failure after a lightning strike. Investigators noted that the Swearingen SA226-AT aircraft had been known to suffer electrical failure in other lightning strike incidents. Another tragic example was LANSA Flight 508, which crashed in 1971 after the Lockheed L-188 Electra suffered wing failure after a lightning strike.

However, more modern passenger airliners from manufacturers like Boeing and Airbus have proven a much more solid safety record when it comes to lightning strikes. This has come as a part of modern regulations, which demand electrical bonding of components to reduce the chance that a lightning strike could ignite fuel vapors or fuel tanks, and panel thickness requirements to make sure lightning strikes can’t easily melt through an entire panel to damage parts inside. Many of these rules were instituted after the loss of  Pan Am Flight 214 in 1963, when investigators concluded that a lightning strike had ignited fuel vapor leading to the total loss of the aircraft.

It’s also worth noting that lightning can actually be a large danger to planes when on the ground. Airports are often large, open areas with few tall structures around, meaning that aircraft can be a more likely target for lightning strikes in the area. In the event a plane is struck on the tarmac, crew nearby can be in severe danger if the strike jumps to them on its way to the ground. Aircraft are often grounded with conductive straps when on the tarmac to help reduce the chance of this happening, and work on the ground is often postponed if there is a high risk of lightning in the area.