What happens if lightning strikes an aircraft?
Summer is the season for thunderstorms, and sometimes lightning can strike an aircraft that is flying. However, a lightning strike on an aircraft is not dangerous, as aircraft are designed to withstand lightning strikes. For an airline the size of Finnair, lightning typically strikes planes dozens of times a year.
The aircraft fuselage is designed to withstand lightning strikes
Pilots try to avoid thunderstorm clouds and fronts. Individual thunderstorm clouds can normally be avoided, but sometimes pilots have to fly through a thunderstorm, which also increases the risk of a possible lightning strike. Thunderclouds can appear in altitudes between one and over ten kilometres. Most often lightning strikes occur during takeoff or before landing when the aircraft is reducing its altitude.
Lightning usually strikes an aircraft on the front side of the plane's cockpit. The edge of the cockpit window is a typical point of impact. The aluminium fuselage of the aircraft conducts electricity well, and due to that, the lightning discharge does not affect the inside of the aircraft. The discharge travels onwards along the outer surface of the aircraft and exits again into the atmosphere, typically from the tips of the wing, control surfaces or the tail of the aircraft.
In aviation, safety always comes first. For an aircraft type approval to be granted, the aircraft manufacturer must demonstrate through extensive certification tests that the aircraft's lightning protection is sufficient. Due to careful testing, the passengers and equipment inside the aircraft are safe.
Passengers often notice a lightning strike by a bang and a simultaneous flash outside the aircraft. It might scare you, but it's nothing to worry about.
Thunderstorms are taken into account in the cockpit and in maintenance
Pilots avoid flying during thunderstorms if possible. Aircraft have a weather radar, which allows pilots to avoid possible thunderclouds along the flight route. When flying at night, pilots adjust the cockpit lighting to brighter mode so that their eyes get used to the bright light in case of a possible lightning strike. As a precautionary measure, pilots also turn on the seat belt sign in the cabin to ensure the safety of passengers and cabin crew in case of turbulence.
As in the cabin, the lightning strike can be seen and heard in the cockpit as well. After the strike, pilots ensure that all devices, such as radios, work normally.
Pilots report the lightning strike to technical staff, and after the aircraft lands, it undergoes a thorough inspection. The most typical areas of damage are overhangs and rivets of the surface plates. Any damages are repaired according to the aircraft manufacturer’s instructions, and after that, the aircraft is ready to fly again.