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Monday, September 20, 2010

Boeing 737 struck by lightning - Can it happen ???

Have you heard of Gauss’s law ? Lightning is one of the most beautiful displays in nature. It is also one of the most deadly natural phenomena known to man. From time immemorial, humanity has had morbid fear of natural forces, more so of lightning and thunder. When it rains heavily accompanied by thunder and lightning. There are many stories in folklore of the devastation caused by the lightning. The deafening sound of thunder puts mortal fear in animals and human being. The fear / phobia is variously known as Astraphobia, Brontophobia and more.

Factually, there is not much to fear as thousands of thunderstorms on Earth each day produce millions of flashes of lightning – most of which occur in tropical areas. Most are harmless. These happen on the sky and what would happen to those sky borne aircrafts when lightning and thunder occur.

Last month, in a tiny island of San Andres in Colombia off Carribbean sea an Aires Airline Boeing 737 with 131 people on board was split into three when it crash landed during a storm. Photos depict it to be a gory accident but fortunately all passengers except one were safe. One died of heart attack. The plane involved Boeing 737 is a short to medium range, single aisle narrow body jet airliner. Boeings have been on air from 1967 ; some reports have it that there could be more than 1200 737s airborne at any given time including those departing and landing.

Scientifically, Lightning is an atmospheric discharge of electricity accompanied by thunder, which typically occurs during thunderstorms and also during volcanic eruptions or dust storms. A bolt of lightning can travel at speeds of 36000 kmph and can reach teperatures of 30000°C hot enough to fuse silica sand into glass. The study of lightning is called fulminology. 

Anybody seeing the scattered remains of the plane would dare think of survivors. The fuselage split in three, pieces of nose and tail facing the opposite direction. Its engine and landing gear broke loose and wreckage remained scattered over 100m up on the runway. For the passengers it was a vacation trip to the beautiful island turned nightmare. From Bogota, San Andres is about 1250 km and would take less than two flying hours.

The transport minister blamed weather conditions and ruled out technical failure stating that it was a new plane which had undergone standard maintenance checks just the week before. Some said it was a miracle that only one died and that the pilot’s professionalism prevented the plane from going off the runway. The jetliner crashlanded at 1:49 am local time at Gustavo Rojas Pinilla airport on the Caribbean resort island. At the time of the accident the visibility was reported at 4000 meters (13000 feet), rain and winds around 15 knots, there were thunderstorms in the area. The plane reportedly spun out of control when it was struck by lightning 80 meters before landing. Though termed as new, the aircraft made its maiden flight in 2003 and entered service the same year.

The one involved in the accident was an Aires Boeing 737-700, registration HK-4682 performing flight 4C-8250 from Bogota to San Andres Island (Colombia) with 125 passengers and 6 crew. It touched down short of runway 06 and broke up in three parts while landing at San Andres Island Airport.

Hospital reports later started 4 survivors needed surgery; the first deceased female passenger was 72 years old and had suffered a cardiac arrest. Another 11 year old girl suffered severe traumatic brain injury and multiple organ failures. She passed away days later.

Boeing and other authorities would conduct investigations into the accident and there could be thousands of questions on what actually happened which made the plane fall apart. The most speculated cause was lightning. Based on weather analysis, 11 lightning flashes had been recorded at a radius of 10km off the airport in the span of five minutes of the occurrence. The Navigation Services Civil Aviation Authority of Colombia also mentioned of extreme weather conditions. There is also a theory that sudden changes in wind direction or airpockets in the path of landing can cause plane slamming the ground.

However there are doubts on the ‘lightning theory’. All aircrafts are designed to avoid adverse effects of lightning strike. The shape and construction which is mostly composed of metal materials, create electrical effects of lightning tends to spread around the fuselage.

The outer skin of most airplanes is primarily aluminum, which is a very good conductor of electricity; the secret to safe lightning hits is to allow the current to flow through the skin from the point of impact to some other point without interruption or diversion to the interior of the aircraft. Science forums state that each commercial airliner averages one lighting hit per year but the last crash that was attributed to lightning was in 1967 when the fuel tank exploded, causing the plane to crash. Generally, the first contact with lightning is at an extremity...the nose or a wingtip. As the plane continues to fly through the areas of opposite charges, the lightning transits through the aircraft skin and exits through another extremity point, frequently the tail.  Aircrafts use modern electronic gadgets as flight instruments. Shielding and surge suppressors ensure that electrical transients do not threaten the on board avionics and the miles of electrical wiring found in modern aircraft.

Aircrafts continuously traverses through changed atmospheric zones and the body of the aircraft has to be protected from lightning. The present day air crafts guided by land control and advanced weather information mostly do not fly into lightning storms, or fly through storms or areas where lightning is likely to be present. There is small device known as "static wick" which is a piece of metal connected electrically to the frame of the aircraft, with one or two spikes or needles on the end. It is housed in a fiberglass rod to insulate it from the airplane. Because the spikes concentrate the electric charge around them, and they are connected to the airframe, they allow the airplane to dissipate any static electricity it may build up out into the air. Also - if lightning strikes the plane, the chances are that the electricity will go through the dissipator and not through the airplane. On the ground, the craft sits on rubber tire and on air it is not grounded.

Thus theories of how and how it cannot always galore and science is mystifying !!!!!

In Physics, Gauss’s law is a law relating to distribution of electric charge to the resulting electric field. It states that ‘the electric flux through any closed surface is proportional to the enclosed electric charge’.

Regards – S(rinivasan)  Sampathkumar.

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