Thursday, April 18, 2013

The unsettling science behind the Lion Air crash

 Lion Air Boeing 737
ndonesian rescue workers help remove a section of a Lion Air Boeing 737 four days after it crashed into the sea near Bali. (Sonny Tumbelaka/AFP/Getty)

For all the headline-grabbing stories about security breaches, intoxicated pilots and faulty equipment, sometimes a commercial plane’s worst enemy is Mother Nature.
That appears to be the case for a new Boeing 737, operated by Indonesian budget carrier Lion Air, that crashed into the shallow waters off the coast of Bali on 13 April, just short of the runway at Ngurah Rai Airport. At the helm was an experienced pilot who managed to save all 108 passengers and crew, but told Reuters it felt like his aircraft was“dragged” down by wind as he fought to regain control. The crash – and the pilot’s alarming comments – are renewing fears about the chilling phenomenon known as windshear.
A windshear or “microburst” is a sudden change in wind speed and direction that can cause planes to rapidly lose altitude. They are often caused by storms creating strong downdrafts of wind.
Airplanes rely on wind speed and direction to control takeoff and landing, typically doing so in the direction of the wind. But sudden shifts in wind speed and direction can cause planes to lose control, especially during takeoff and landing, when they are low to the ground and have reduced engine power and little room to manoeuvre.
How likely is it that Lion Air’s crash was caused by a windshear? Officials from a bevy of agencies – including Indonesian state officials, the US National Transportation Safety Board, the Federal Aviation Administration(FAA), the Meteorological and Geophysics Agency and Boeing – are investigating the incident and expect to release their findings within a month. But initial tests show that the pilot was experienced, was not under the influence of drugs or alcohol, and the plane, a brand new Boeing 737, had no technical issues, all of which rules out pilot or plane error.
What’s more, weather reports indicate a strong storm and driving rains were developing as the plane attempted to land, which lends support to the idea of windshear as the culprit.
But the surprising – and unnerving – point is that aviation officials consider windshear to be a problem that was solved long ago. Between 1964 and 1985 windshear was responsible for some 26 civil aircraft crashes in the US, leaving about 500 fatalities and about 200 injuries,according to NASA.  The most famous incident involved a Delta Airlines Lockheed Tristar, which crashed in 1985, killing 134 passengers and crew near the Dallas-Fort Worth airport.
Since then, windshear-related incidents have dropped considerably, thanks to FAA- and NASA-developed technology that warns pilots of oncoming storms. The Predictive Windshear System, available below 700m, warns pilots some 10 to 40 seconds ahead of windshear to go around the bursts.
But for now, a lot of unknowns remain, including whether the Lion Air crash was caused by windshear, whether the windshear warning system was functioning on the aircraft and perhaps the biggest question for the airline industry – whether windshear may again become a serious concern.

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