Answer: Lightning

Statistically, every airliner in the world is struck by a bolt of lighting at least once per year (and those that fly through frequently stormy regions are stuck with even higher frequency). Although it sounds terrifying, unless a passenger happens to be looking out the window in the right direction at the exact moment it happens, they likely won’t even notice.

The electricity of the lightning strike is conducted over the aluminum skin of the aircraft and then continues towards the earth. Although historically lightning strikes could spell serious trouble for planes (by inducing sparks in areas where fumes had accumulated for example), after a Pan Am 707 airplane crashed in 1962 after being struck by lightning, industry regulations were revised and tightened. Modern planes feature a wide array of lightning protection and electrical suppression mechanisms.

Thanks to improved safety measures and mechanisms, it’s far safer to be in the plane when the thunderstorm comes than it is to be on the ground at the airport.