Watch out for calamity cloud

Captain Chetan Shah must have got the jitters when he heard about the Air France crash on Monday.
For he was the commandant of a Jet Airways flight from Calcutta to Mumbai that flew straight into a thunderstorm — quite like the one that probably felled the flight over the Atlantic — on April 12, 2007, with 160 passengers on board.
Pilots know that a thunderstorm is common over our skies at this time of the year. But Captain Shah knows more about it than he would have ever liked to.
“The presence of a 17km tall column of cumulonimbus cloud bearing charged particles, some of more than 1,000 volts, enough to electrocute the plane, was not monitored on his weather radar screen in the cockpit,” recounted an official of the Directorate General of Civil Aviation (DGCA) official, which had conducted a probe into the close shave.
“The aircraft flew straight into it a few minutes after take-off and was facing severe turbulence. It was so severe that he thought it was the end,” the official added.
Shah had cried “May Day” to the Calcutta Air Traffic Control (ATC) while turning the aircraft, a Boeing 737, left and steering it out of the cloud. Then he told the ATC that the “emergency was cancelled”.
“There is frequent formation of cumulonimbus clouds (tall, dense and dangerous) in Bengal, especially in the pre-monsoon period from April to June,” said a senior official of Calcutta airport’s Met department.
Sometimes, the thunderstorm is perilously close. On June 6, 2006, a Jet Airways flight from Mumbai to Calcutta was struck by lightning while passing through a thunderstorm.
According to Met officials, the cumulonimbus cloud can form alone, in clusters, or along a cold front in a squall line.
04/06/09 Sanjay Mandal/The Telegraph

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Categories: Safety Jun 2009