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. In addition, the bases of the thunderstormswere high enough that cloud-to-ground lightning strikes were harder to come bydue the insulation affect of the air between the ground and cloud base. Theairplanes being closer to the clouds became the closer target for thelightning.Although the lightning strikes were loud, bright and nerve-racking forpassengers, the planes were safe from them.
The preliminary FAA report on the 3 incidents as reported by WPVI-TV inPhiladelphia states...
AirTran Airways Flight 628, Boeing 717, landed on runway 27R at 6:22
p.m.after reporting it had been struck by lightning. aircraft declaredemergency, landed safely.
Republic Airlines Flight 3407, an Embraer 170, reported being struck by
lightning over NE Philadelphia at 6:15 p.m., landed runway 27L at 6:20p.m.
Did not declare an emergency.
America West Flight 1036, a Boeing 757, reorted being struck bylightning three minutes (6:18 p.m.) after RPA Flt 3407 was hit. Aircraftdeclared emergency, landed on runway 27L at 6:34 p.m.
FAA inspectors will examine each aircraft today to determine if therewas any damage.
Republic Airlines crew reported no damage last night. America Westreported some, and AirTran crew reported the aircraft was struck "righton the nose."
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.
Story by AccuWeather.com Senior Meteorologist Henry Margusity
