Dan Blewett is the co-host of STRUCK, an aerospace engineering podcast.
How Often Are Planes Struck by Lightning?
The Federal Aviation Administration (FAA) estimates that commercial planes are struck by lightning approximately once every 1000 flight hours. This converts to about one lightning strike per year, on average, per plane.
Yet, despite consistent lightning strikes on commercial aircraft, it's exceedingly rare that planes crash or have other airborne accidents due to lightning. So, what is protecting commercial airliners from lightning strikes, and how do they not crash when hit by such powerful bolts of electrical energy?
How Lightning Exits an Airplane
Before we talk about how airplanes are protected from lightning, let's talk about the overall path a lightning bolt wants to take. Lightning strikes the aircraft because electric charge builds up on various parts of plane. Small water and ice particles cause electrical charge to build at the nose, radome, and other parts, so aircraft actually have the ability to cause lightning strikes rather than simply being an innocent bystander in the wrong place at the wrong time.
We know that electricity always follows the path of least resistance, and commercial airliners are made of aluminum skins with airframes made of a combination of metal and composite materials. For commercial airliners, when lightning energy reaches the aluminum skin of the aircraft, it spreads out and flows safely toward the bottom or rear of the plane before passing back into the air toward the earth. Cloud to plane to ground is the overall path the lightning strike will take, and when it flows mostly through the metal skin of the airplane, major damage is avoided.
Composite Structures Take the Most Damage
The problem, however, is that planes are made of a combination of composite and metallic structures. A radome is a composite enclosure that houses sensitive radar, satellite, antenna, and other equipment.
The problem with radomes is that they are on the nose of the aircraft (and house protection, weather, and radar equipment) and on the top (where they provide satellite communications, antenna functions, and in-flight wifi). These locations are highly susceptible to lightning strikes and because these radomes are made of composite materials, they'll be damaged if struck.
Composite structures like radomes will suffer burn or puncture damage if struck, potentially requiring replacement of not only the sensitive equipment inside but also the entire expensive radome.
Lightning Diverters Protect Radomes
The most common protection for composite radomes on an aircraft are segmented lightning diverter strips. Lightning diverter strips provide a path for lightning energy to flow over, thus protecting the aircraft's delicate composite radomes.
Lightning diverters work by forcing the electrical energy to jump from segment to segment through the air rather than flowing through the composite material, which would severely damage it. This keeps composite radomes—and the sensitive equipment inside—intact.
Lightning-Protection Technology Continues to Improve
Aircraft come in all shapes and sizes, and many smaller planes have carbon-fiber or composite bodies that need significant lightning protection. Because these planes don't have the metal skin that helps safely divert lightning energy, they are more at risk for significant damage if struck.
Expanded metal foil is one technology that is applied to carbon fiber aircraft parts to help spread out the energy of a lightning strike. This helps reduce puncture damage incidents and improves overall safety. Carbon fiber with wire weave is also used when building aircraft parts from carbon fiber, as the interwoven wire helps dissipate lightning energy.
These techniques, along with lightning diverters and other technology, can help reduce the impact of a lightning strike and keep an aircraft and its passengers safe from mother nature.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2020 Dan Blewett