June 2, 2009
Modern Jets May Be More Vulnerable To Lightning
Experts say passenger jets are hit by lightning every 1,000 hours (on average twice a year) and the risk from the bolts of electricity continues to be an increasing problem, AFP reported.
However, after the disappearance of an Air France jet in the Atlantic with the feared loss of 228 lives, technical experts say lightning alone could not have caused it to crash into the ocean.The A300-200 jet was likely hit by lightning as it passed through a violent storm on the flight from Rio de Janeiro to Paris on Monday, according to Air France.
But Pierre-Henry Gourgeon, Air France's chief executive, said the plane suffered multiple technical failures before falling off radar screens.
He said the jet sent a succession of a dozen technical messages that showed "several electrical systems had broken down" which caused a "totally unprecedented situation in the plane."
Gourgeon suggested it was probable that the plane had an impact with the Atlantic shortly after these messages were sent.
Vincent Fave, an expert airline accident investigator, told AFP that while lightning could cause a mechanical problem or pierce the aircraft, it can usually continue to fly.
A lightning strike could damage a plane's communications and navigation systems, according to Yves Deshayes of the French national airline pilots union (SNPL).
"But in a plane the systems are doubled, even tripled, so a lightning strike that threatens the security of a flight, and even the state of the aircraft, is extremely rare," he said.
A lightning strike could explain why there was no radio contact with the Air France plane, but nothing more, Deshayes said. He said it was hard to imagine lightning hitting a plane and making it explode.
"To my knowledge there are no incidents of planes which were blown up by a lightning strike," he said.
Aircraft are designed to survive lightning strikes, according to David Learmount of Flight International magazine, but he noted the disappearance of the Air France jet was a "chilling reminder that nothing is impossible, however unthinkable."
Francois Grangier, an expert on aircraft accidents, told AFP in a 2005 interview of his experience: "In my career as a pilot I often experienced lightning as did all of my colleagues. It's something which is often impressive, it makes a lot of noise in the aircraft and usually electrical power fails, but it's just as if it happens at home: the fuses jump, you put them back and everything works."
He said the electrical impact usually spreads across the surface of the aircraft "along the external skin, in aluminum alloy which is a very good conductor of electricity, and the fuselage and wings act as a Faraday cage."
Any external metallic frame prevents lightning from traversing the structure under the Faraday phenomenon.
But many manufacturers are bypassing aluminum for composite materials based on carbon fiber and resin because they offer weight, and therefore fuel, savings.
Boeing's new generation 787 Dreamliner makes extensive use of such materials, but experts say composite materials are less effective in deflecting lightning and manufacturers have turned to another way of providing a shield.
Many companies now use the 'metallization' of the aircraft: a kind of mesh is added, a superficial layer which acts as a Faraday cage protecting the aircraft.
At least two air crashes are believed to have been caused by lightning in recent years.
Chinese authorities say a bi-turboprop Yun 7 belonging to the Chinese carrier Wuhan Airlines was hit by lightning on June 22, 2000 as it approached Wuhan airport.
Forty-two people on the plane and seven on the ground perished when the plane crashed into a boat.
A Kenyan Airways Boeing 737-800 on its way from Abidjan in Ivory Coast to Douala, Cameroon on May 5, 2007 went down in a violent storm and all 114 people on the plane were killed. Lighting was the suspected cause of the crash.
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