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Posted at 02:00 PM ET, 05/17/2011

Airline safety: Is the fear of a lightning strike warranted? JetBlue plane struck


Still image of plane being affected by lightning flash (NOAA)
This morning, the New York Daily News reports a JetBlue flight declared an emergency after it was struck by lightning on its descent to JFK International Airport.

“The electrifying episode caused passengers and crew to smell smoke on board, leading the pilot to ask that emergency vehicles meet the plane upon landing,” it said.

No one was hurt.

That’s wasn’t the case on December 8, 1963, a 5-year old Boeing 707 Pan American World Airways jetliner crashed near Elkton, MD, killing a total of 73 passengers and 8 crew members. The plane, en route from Puerto Rico, had stopped at Baltimore and was on its initial approach to Philadelphia, the final destination. Since thunderstorms were in the vicinity, it was thought that lightning had caused the vapors in a reserve fuel tank to explode.

You should know that that accident—almost 50 years ago--represents the last time that lightning was responsible for commercial U.S. airline casualties. A very good record indeed!

Nevertheless, as evident from this morning’s Jet Blue incident, lightning does strike airliners all the time. In fact, according to Edward J. Rupke, senior engineer at Lightning Technologies, Inc., (LTI) in Pittsfield, Mass., lightning hits each U.S. commercial airliner “lightly” more than once each year. Rupke asserts that the planes themselves “often trigger lightning when flying through a heavily charged region of a cloud [when natural lightning has ceased-see below].…when the lightning flash originates at the airplane and extends away in opposite directions.”

On April 23rd, 2011, a London videographer captured a spectacular lightning strike of an Emirates Airlines Airbus A380 jetliner on its final approach to Heathrow Airport. (See Jason Samenow’s post of May 12th.) Although the circumstances of this lightning strike are unclear, the video, now gone viral, might argue against a “triggered,” strike, as described by Mr. Rupke.

However, Vlad Mazur, a NOAA lightning expert, maintains that the Emirates incident was “without doubt a triggered flash.” According to Mazur, natural lightning had probably already ended but left behind a highly charged electrical field. In such situations, Mazur contends that without a “natural mechanism” to initiate a lightning discharge, it takes an “artificial trigger,” such as an airliner.

So how has the airline industry been so successful in protecting planes from lightning damage during the last 47½ years? Advanced radar systems, of course, play a big role in this safety record, as more than anything else, detection and avoidance is the primary goal, mirroring the lightning safety advice of the National Weather Service reflected in this blog last year. Airliners cannot fly over the towering cumulonimbus clouds of thunderstorms--which can reach 50,000 feet or more--but they usually can fly around them. A solid line of thunderstorms stretching hundreds of miles can be dealt with by delaying the takeoffs of planes which must cross that line. Turbulence in and around thunderstorms is generally regarded as the greater threat.

Despite the best of efforts, sometimes airliners are struck by—or trigger—lightning discharges. When an airliner is struck at one of its extremities, the lightning often travels along the metallic surface* of the plane and exits at another extremity, such as a wing tip. Often a “bang” or “pop” is heard, which is more alarming than anything else. (Having experienced this once, it is not a comforting feeling.)

A Qantas flight a struck by lightning mid-air on its descent to Sydney on September 5, 2004.

But according to engineer and lightning expert Rupke, the real danger lies with the possibility of “transients,” or power surges, entering the aircraft and damaging its sensitive electronics or a spark somehow entering the fuel system, the probable cause of the 1963 accident. Airline experts have now largely succeeded in resolving these issues, so that today’s aircraft must pass a rigorous and exhaustive set of criteria before they can be certified.

Rupke says that to prevent the above types of electrical breaches and insure the integrity of an airliner’s “skin,” great care is taken to eliminate the slightest gap in a plane’s exterior surface. As for the fuel system and associated vapors, not only must the fuel tanks themselves be sufficiently thick to withstand a “burn-through,” but all rivets, joints, and other connectors must be designed to withstand a lightning discharge. Last (but certainly not least), today’s jet fuel is much less volatile than that of the past, when explosive vapors were of even greater concern.

So what are your traveling plans? Will the prospect of thunderstorms en route deter you? Have you ever been in a plane and realized at the time that it sustained a lightning strike? Personally, my wife and I will be flying off to Minneapolis soon—thunderstorms or not.

*Aircraft surfaces are increasingly being built with composite materials, which are lighter and less conductive than aluminum, the favored material of the past.

By  |  02:00 PM ET, 05/17/2011

Categories:  Lipman, Latest, Science, Thunderstorms

 
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