Plane & Pilot
Tuesday, June 21, 2011

Lightning!


Lightning may not be a major hazard for aircraft, but it’s the most spectacular manifestation of our archenemy the thunderstorm


The first known instance of a lightning strike bringing down an airplane was in 1940, when a DC-3 crashed in Lovettsville, Va. Since then, there have been a few other accidents, but very few. One common scenario that can cause a crash is a strike on a mostly empty fuel tank. If the air/fuel mixture approaches the optimum 15 to 1, and an electrical charge penetrates inside the tank, the results can be catastrophic.

Serious lightning accidents are so rare that the last verified instance of a strike causing an accident was in 1976, a Boeing 747 freighter in Spain. (The verdict isn't in yet on the 2009 crash of Air France 447, an Airbus 330, into the South Atlantic off Brazil. As we go to press, the data recorder has been recovered from 13,000 feet of water, but it's not known if there's any usable information on the tape.) Composite airplanes have less natural resistance to lightning damage, and therefore are fitted with an imbedded layer of conductive fibers or metal screening material.

General aviation aircraft aren't immune from lightning strikes, but their exposure is minimal, as they typically operate at lower altitudes and rarely in close proximity to thunderstorms. Also, personal aircraft are usually smaller and less liable to attract or generate lightning. Large corporate aircraft that operate in the airline environment are more likely to suffer damage. I once inspected a Beech Starship in New Mexico that had been severely damaged by a strike, forcing the crew to make an emergency landing at the Albuquerque Sunport.

Back in the 1970s, NASA conducted in-flight tests to study the effects of lightning strikes on aircraft. The research team from the NASA Storm Hazards Project flew into more than 1,500 thunderstorms, and their aircraft were struck by lightning over 700 times, usually with no adverse consequences to the airplane. It's a safe bet they did have to clean up the interior after each flight, however.

Incidentally, let no one infer that I'm suggesting thunderstorms aren't dangerous. All pilots know that they can be killers. It's thunder and lightning that's often more bark than bite. I hope no one concludes that I treat the severe weather associated with Cb activity lightly. In fact, the opposite is closer to the truth. Many of the places I fly have no alternates, so I'm actually more conservative than the average bear. I often don't have the option of landing and waiting for the nastiness to pass, so I often don't even depart when thunderstorms are menacing the route. Other pilots with the option of diverting or landing short may opt to take a look, then change the route or forget the whole idea.

Going into Brisbane, Australia, in a Caravan several years ago, I held for two hours out over the Coral Sea, waiting for violent lightning storms to move west, wondering what I'd do if they didn't. Fortunately, the boomers gradually rolled through the area, and I was able to land before fuel became critical.

Despite its spectacular noise and flash, lightning may not be a major hazard for general aviation aircraft, but avoiding it and the often violent weather that accompanies it is simply good sense.




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