Aircraft a magnet for lightning

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Aircraft frequently get struck by lightning but with improved design and technology they are built to weather it.

THE weather forecast had warned of rain with thunderstorm that fateful day, the preliminary report on the Sebuyau helicopter crash confirmed last Thursday, and there was indeed heavy rainstorm, lightning and thunder in the Eurocopter AS350’s route.

But with main body of the helicopter still missing, the actual cause of the tragedythat killed Deputy Plantation Industries and Commodities Minister Datuk Noriah Kasnon, Kuala Kangsar MP Datuk Wan Mohammad Khair-il Anuar Wan Ahmad and four others could not be determined.

And neither could the claims of villagers from Kampung Seduku, located some 46km from the crash site in Sebuyau, that they had seen a flash of lightning hit the helicopter, causing it to become unstable and crash.

According to experts, aircraft get struck by lightning frequently. Luckily, with improvements in design and technology, they are built to weather it.

The danger remains, however, says director of the Centre for Electromagnetic and Lightning Protection Research (Celp) at Universiti Putra Malaysia, Prof Ir Dr Mohd Zainal Abidin Ab Kadir.

Although the design and material used for choppers are able to withstand any high current, its small size, compared to the size of commercial aircraft, can easily cause the pilot to loose control of it, says Prof Dr Zainal.

He adds, the high electromagnetic field caused by lightning can also interfere with the electrical and electronic systems of the aircraft.

“That’s why we have to listen to and make use of weather forecasting to help us,” he says.

Lightning expert Hartono Zainal Abidin agrees that despite the design upgrading of rotary wing aircraft like helicopters, it is still not recommended for a helicopter to fly if a thunderstorm has been forecasted or is in progress.

Helicopters are normally struck at the main and tail rotor blades, he points out.

“Since modern rotor blades are not fully metallic – they are usually made of compo­site material or carbon fibre – they can be damaged by lightning if the lightning current is large.

“A damaged rotor blade spinning at very high speed can destabilise the entire rotor blade system and lead to major loss of power. This can result in the helicopter losing height quickly and crashing. The pilot will not have time to radio his emergency since he is struggling to control the helicopter,” he says.

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Another “threat”, he adds, is the high lightning flash density in the country.

Highlighting the regular occurrences of helicopters being struck by lightning over Europe’s North Sea in winter, Hartono says one study suggested that it is the presence of helicopters in the sky that triggers the lightning to strike them.

“But the lightning flash density over the North Sea is less than one flash per sq km per year.

“However, in this country, the lightning flash density is about 50 times higher. Hence, a helicopter flying through a thunderstorm in this country is 50 times more likely to be struck by lightning than a helicopter over the North Sea,” he opines.

With the seemingly increased incidences of airplanes hitting stormy “turbulence” reported in the media, some are getting worried about ordinary airplanes getting thumped by these electric bolts.

Ordinary airplanes or fixed wing aircrafts are normally struck by lightning at the nose cones and wing tips, says Hartono.

But as the bodies of modern aircraft are made of metal, the current is conducted around the shell of the plane without letting it in, he says.

A person inside any metal structure (called a “Faraday cage” in physics) is safe because lightning will move along the metal but not into the cage.

According to Lightning Technologies, Inc, planes’ electronics and navigation equipment are grounded and protected from electrical surges while fuel tanks have built-in lightning protection to ensure they can withstand a lightning strike without catching fire.

“Even though these may be damaged by lightning, airplanes do not normally lose engine power and even if they lose power, they can still glide,” Hartono assures.

Take Malaysia Airlines flight MH1348 bound for Langkawi from Kuala Lumpur; in 2014, it was reportedly struck by lightning. The flight landed safely at the Langkawi International Airport.

Still, this doesn’t mean we should underestimate thunderstorms – their greatest danger to aircraft comes from the winds and turbulence they generate.

And sometimes, this happens: In 2013, a domestic Turkish Airlines flight from Istanbul carrying 114 people was hit in its engine by a lightning bolt, causing it to burst into flames. Luckily, the plane made a safe emergency landing, even as sparks and flames crackled from its crippled engine.

Source: The Star Online. Sunday, 19 June 2016