What happens when lightning hits an airplane?
Planes are hit by lightning more often than you think - but what actually happens when they are?
It’s the moment you’ve never been waiting for.
You're tucked up under your airline blanket, nose in book, when, suddenly, a flash of bright light streaks through the aeroplane. You – well, the plane with you in it – has been struck by lightning. But do you need to panic, brace, or reach for a lifejacket?
In an incident this week, Air New Zealand flight NZ433, bound for Wellington, was struck and had to turn back to Auckland as a "precautionary measure" to undergo standard checks before returning to service.
Passengers were put onto a different plane and, despite assurances from the airline that lightning strikes are very common, some were reportedly apprehensive about heading back up into stormy skies.
So what actually happens when lightning hits an aeroplane, and why are they not seriously damaged?
Typically, a bolt will hit an extremity, such as a wing tip, or the nose, and the current will travel through the aeroplane’s metal shell before leaving from another point – the tail, for example. And, according to Patrick Smith, pilot and author of Cockpit Confidential, a book on “everything you need to know about air travel”, planes are hit by lightning far more frequently than you might think.
“An individual jet liner is struck about once every two years, on average”, and aeroplanes are designed accordingly. “Once in a while there’s exterior damage – a superficial entry or exit wound – or minor injury to the plane’s electrical systems, but a strike typically leaves little or no evidence.” You might not even notice it, he says.
Professor Mamu Haddad, professor and director at Cardiff University's Morgan-Botti Lightning Laboratory, which works on understanding lightning strikes on aeroplane construction materials, explains further.
Modern aircraft, he says, are made from lightweight carbon composite covered with a thin layer of copper – Dreamliners and Boeing Airbus A350s have this construction – and act as very good Faraday Cages, meaning that the space inside the metal (ie where you’re sitting) – is protected from electric currents.
Most important, he adds, is that the fuel tanks in the wings are not exposed to any lightning sparks – hence why the surrounding metal, structural joints, access doors, vents and fuel filler caps must be able to withstand any burning from a bolt of lightning, which can have temperatures of up to 30,000C.
Strikes are most likely to happen when a jet is passing through cumulonimbus (storm) clouds, between two and five kilometres (6,500-16,500 feet) from the ground. And, like Patrick Smith, Prof Haddad says that fliers need not be concerned.
“Lightning can be up to 200,000 amps – at a low current people might hear noise, or see a flash of light through the window, but they won’t feel anything," he said. "One effect on the aircraft body might be some local melting, where the lightning struck, but the aerospace industry is highly conservative, and testing so rigorous, that passengers aren’t at risk.”
Rare though they may be, there have been a few fatal incidents involving lightning strikes, however. In January 2014, four charred bodies were reportedly pulled from plane wreckage in Indonesia after a light aircraft owned by Intan Angkasa Air was hit by lightning and crashed. Bambang Ervan, an Indonesian transport ministry spokesman, confirmed to an Australian news site that all four people on board the aircraft were killed instantly.
In 2010, two people were killed when a Boeing 737-700 from Bogota was struck by lightning and split into three pieces as it landed at San Andres island in the Caribbean. At the time, aeronautical specialists explained that the lightning alone was unlikely to be the cause of the accident, but combined with a sharp change in wind direction, or an air pocket linked to lightning when a plane is near the ground, it could cause a crash.
Another serious case, resulting in 81 deaths, happened in 1963, when a lightning strike over Maryland caused a wing to explode on a Boeing 707 flown by Pan Am. The Federal Aviation Administration, the US equivalent of the Civil Aviation Authority, subsequently introduced changes to fuel tanks and discharge wicks aboard all aircraft.
But non-fatal incidents are far more common, thanks largely to modern safety measures. Famous cases include the flight taken by François Hollande, the French President, to crucial talks with Angela Merkel in Germany in 2012.
The presidential Falcon 7X was struck by lightning just four minutes into the flight; Mr Hollande eventually arrived in Berlin 90 minutes late, on a different plane.
Patrick Smith remembers having a close encounter with lighting when he was at the helm of a 37-seat aeroplane.
“Lightning from a tiny embedded cumulonimbus cell got us on the nose," he says. “What we felt and heard was little more than a dull flash and a thud. No warning lights flashed, no generators tripped off line. Our conversation went:
‘What was that?’
‘I don’t know.’
‘Might have been.’
Mechanics would later find a black smudge on the forward fuselage.”
In other words, an incident is likely to be over in a flash, literally, leaving passengers on board to get back to that in-flight film. It’s often those on the next flight who could be delayed, as the plane undergoes post-lightning safety checks.
Read more:Why do flight attendants dim the lights for takeoff and landing? Confessions of an airline pilot: What really goes on in the cockpit? Nervous Fliers Q&A: What is turbulence? What if lightning strikes, or autopilot fails?