The last airplane disaster that has been directly attributed to the plane being struck by lightning occurred in Germany in 1988. On Tuesday, a Delta flight from Milwaukee to Atlanta was struck by lightning and forced to divert to Chattanooga. While forced diversions and crashes are rare, according to estimates, every plane in the U.S. commercial fleet is struck by lightning at least once a year.
So why aren’t there more crashes? The reason is better safety regulation. Since 1963, when the last lightning-caused fatal crash in the United States, the Federal Aviation Administration (FAA) has required more testing of an aircraft’s fuel storage tanks to make sure that a lightning strike cannot trigger a spark that might cause the tank to explode.
The highest probability for a lightning strike on an aircraft is during a plane’s climb after takeoff and during its descent for landing because lightning occurs more often at altitudes of 5,000 to 15,000 feet. Virtually all (96%) of all lightning strikes on airplanes occur between those two altitudes. According to a technical report from Boeing, planes flying short routes in parts of the world where lightning activity is greatest are “likely to be struck more often than long-haul flights” operating in areas where lightning is less common.
Nearly three-quarters (70%) of lightning strikes occur during a rainstorm. The conditions that cause rain also may cause clouds to store electrical energy, and that stored energy becomes available to create lightning.
Lightning can affect aircraft up to five miles away from the center of the cloud holding the energy. Nearly half (42%) of pilot reports of lightning strikes came during times when no thunderstorms were in the same area.
In the United States, parts of Florida experience an average of 100 thunderstorm days per year, making Florida the most likely place in the country for a lightning strike. Along the U.S. West Coast, the thunderstorm days average is around 10 per year, the least in the country.
When a plane is struck by lightning, the bolt usually attaches itself to one place and exits at another. The five areas of the plane where lightning typically first hits are the radome (nose), forward fuselage, nacelle (engine covering), tail assembly (empennage) or wing tip.
When the bolt hits the plane, the nose or wing tip may glow as the air around the leading edges of the aircraft are ionized. In the next stage, the ionized air forms pathways leading away from the plane that may then collide with energy from a cloud, causing the flash and bang that crew and passengers see and hear. As the lightning strike pulses, the electric current travels through the plane’s metal skin and structure and exits, usually through the tail, while seeking an opposite polarity or ground.
While it sounds awful, modern airplanes are designed and built to take this kind of abuse. The thickness of the plane’s metal skin is enough to protect the interior of the plane and also protect the plane’s electrical systems. Lightning protection also includes wire bundle shields, ground straps and other composite and metal structures.
What this all means is that even though every plane in the air can expect to be hit by lightning once a year, the damage to a plane is typically small and there are virtually no fatalities related to planes that tangle with lightning. Feel better now?