The question of how jets survive direct strikes by lightning was raised again recently when an Airbus 380 from Dubai was struck by lightning while approaching the runway at Heathrow Airport in London. The lightning strike was caught on camera, which captured the world's imagination and begged the question how an aircraft can survive such a spectacular and powerful phenomenon.
According to Natalie Wolchover on LiveScience.com, in cooperation with Lifeslittlemysteries.com, the average commercial aircraft is struck by lightning a little more than once a year, so it is actually quite a common occurrence. What has prompted public interest in the recent Airbus 380 incident is the fact that it was captured on camera, which is actually quite rare.
Scientists now believe that airliners actually cause the lightning which results in direct strikes to jets by flying through storm clouds. The metal of the plane itself intensifies the storm cloud's electrical field and a direct strike is the result. This can result in an electrical breakdown, but in general jets survive these incidents intact.
Vlad Mazur, an atmospheric scientist at NAOA (the National Atmospheric and Oceanic Administration) said of the Heathrow flight: "In decaying storms you have a very high electrical field. It's enough to support the development of lightning, but there is no natural mechanism for initiating lightning discharge. When an airplane comes in, it acts as an artificial trigger."
Passengers on a jet struck by lightning are protected in the same way as a person driving a car struck by lightning - the phenomenon is known as a Faraday Cage, where the lightning is conducted all around the metal body without affecting any people within (as long as the people in question aren't in contact with the metal exterior and are well insulated).
For the jet itself, modern aircraft are designed so that the plane's body acts as a conductor, with a positive charge building at one end of the aircraft, and a negative charge at the other end. According to Mazur, the charge tends to build at points on the plane's largely aluminium shell where the curvature is quite sharp: wing-tips, the plane's nose, and the tip of the tail. Then just a single spark is required to initiate the development of a plasma channel (or a bolt of lightning, in other words).
In general though, these direct strikes are spectacular but harmless. Electricity flows over and around the plane, but not through it. Out of over 140,000 aviation accidents in the NTSB (National Transportation Safety Board) records, just 24 are lightning-related, and only five resulted in fatalities. These are great odds when you consider that the average aircraft is struck by lightning at least once a year!
The most serious lightning-related accident on record occurred in 1963, when a direct strike ignited a fuel tank and the resulting explosion killed the entire crew and 81 passengers. These days, jets like the Airbus 380 are designed so that the electricty from a lightning strike flows over the fuselage and away from critical systems. Fuel tanks are tested to make sure they can withstand direct strikes without producing deadly sparks and electronic systems are grounded to prevent disruption.
Jets survive direct strikes by lightning intact because the Faraday Cage principle protects passengers within from the electricity flowing over the surface, and clever engineering and safety testing minimises the risk to fuel tanks and other critical systems. A lightning strike is a common but still not a trivial occurrence for a commercial aircraft.