In the early 1970s, a number of aircraft crashed in the United States in similar circumstances - and yet the underlying cause was far from clear. They all took place at landing or takeoff, in the immediate vicinity of thunderstorms, and it looked as if the pilot had suddenly, and completely, lost control. In 1975, when an Eastern Airlines jumbo jet came down near Kennedy, the report on the accident coined a new word for meteorologists and aviators: the microburst.
There are always dangers associated with flying through a thunderstorm. An obvious one is lightning, but while a lightning strike can be unpleasantly spectacular, it very rarely causes serious damage to the airframe, and the tightly bonded metal shell prevents the current penetrating the interior.
Airframe icing is also a problem. But the real villain of a thunderstorm is the severe turbulence associated with the powerful currents of air that surge upwards in some parts of a thundercloud, and downwards with equal ferocity in others.
A microburst is a particularly vicious and highly localised downdraught - a sudden downward gush of air that hits the ground and bursts out horizontally around the point of impact, rather like the stream of water from a tap when it strikes the bottom of the kitchen sink. A full-blown microburst is a rare event in western Europe, but they are not uncommon in the US and Australia, where the thunderstorms are more vicious than the worst experienced here.
An aircraft that flies into a microburst when landing first encounters an unexpected headwind, which increases lift; seconds later comes the downdraught, whose effect on the behaviour of the aircraft is exacerbated if the pilot has already compensated for the upward thrust just recently encountered; and finally a tailwind results in a sharp drop in airspeed, and even more rapid loss of height. The vicious sequence of sudden, unexpected wind-shifts may be lethal.
Today's aircraft, although safer and more sophisticated in many ways, are sometimes more vulnerable to turbulence than their older counterparts. The older, smaller aircraft bounced around like leaves in an autumn storm, avoiding serious mishap; today's jets have a heavier wing-loading, and their engines take longer to respond to pilot input. But modern technology has at least improved the art of sensible anticipation: with Doppler radar it is possible to "see" the wind, and identify the most turbulent zones within or near a thunderstorm - usually allowing the pilot to avoid the immediate areas of danger.