Unusual Cold Leads to Planes Hit by Lightning

The unusually cold weather across the Northeast this week was the culpritfor the lightning strikes on the planes landing at the PhiladelphiaInternational Airport. Why? The freezing level was only about 3,000 feet abovethe ground, which is a level that is more common in March. The air aloft wherethunderstorms grow was very cold with temperatures lower than 10 degrees upthrough 15,000 feet. That means any thunderstorms that develop will immediatelyhave ice crystals and hail that lead to the charge separation that produceslightning. Now, add an airplane with a metal casing flying through a highlycharged cloud and bang, a lightning strike is produced. In Thursday evening'sflight, the storms moved into the approach path to Philadelphia InternationalAirport; two airplanes most likely encountered the highly charged clouds andprobably generated the strikes. Lightning strike data in that area did not showany cloud to ground strikes, which leads to the theory that the planesthemselves generated the strikes.Although the lightning strikes were loud, bright and nerve-racking, theplanes were safe from them.

It is estimated that every commercial airplane is hit by lightning at leastonce per year. With tight schedules and the sheer number of planes in the air,it is inevitable that a commercial airplane will eventually be hit bylightning. The fact is that in most cases the airplane will actually triggerlightning when flying through a heavily charged cloud. The aluminum casing ofthe airplane combined with the friction produced as the plane flies through thecharged cloud will result in a lightning strike that originates at the planeand extends away from the plane. It's the same principle of a person walkingacross a carpet and causing a static charge shock when the person comes incontact with a metal object or another person.

The airplane itself is engineered to be protected by lightning strikesdespite all the electronicsand computer systems. The last known commercial crash due to a lightning strikeoccurred in 1967. Since then, millions of airplanes have been hit by lightningor generated lightning with little incident.