Read Understanding Air France 447 for Free Online Page A

fueled by global circulation patterns known as the intertropical convergence zone (ITCZ).
    Soon after the accident occurred, it was a reasonable guess that they had flown into a large thunderstorm and suffered severe damage, which brought the airplane down. After all, the airplane flew through an area of known severe thunderstorms and was lost minutes later.
    A detailed meteorological analysis of the flight was done by Tim Vasquez, a meteorologist who did weather route forecasting for the US Air Force in the mid 1990’s. His excellent analysis can be found at his Weather Graphics website: http://www.weathergraphics.com/tim/af447/. If you are at all interested in the more technical aspects of the weather, do not miss this site. Several graphics in this publication are provided courtesy of Mr. Vasquez.
    Weather does play a part in this accident. The crew flew into an area of heavy weather, with only a slight deviation from course. The pitot tubes became clogged and shortly thereafter the crew was unable to maintain control of the airplane.
    But airplanes have been dealing with thunderstorms and icing for the better part of 100 years, and in high altitude jets for over 50. So what happened here?
    The evidence points to a unique combination of the characteristics of the inter-tropical convergence zone, and the specifics of particular models of pitot tube used by Airbus.
    The A330-200 and -300 models were launched in 1994 and 1998 respectively. It would be 2008 before this pitot tube issue was known and well after the accident before it was understood.
    The ITCZ
    The ITCZ is a region that circles the globe near the equator. The zone moves slightly north of the equator in the northern-latitude summer (May-September), as it was on the night of the accident. 8 Unlike land-mass thunderstorms which are often driven by convection from below or by frontal action, the thunderstorms of the ITCZ are driven by global circulation patterns with warm moist air coming from the equatorial region. The prevailing easterly trade winds of the Northern and Southern hemispheres converge provide the lifting action required to create a storm. As with all thunderstorms, when the air rises it expands and cools leading to cloud formation.
    The tropopause is the dividing line between the troposphere and stratosphere and acts like a ceiling on vertical storm development. It is the point at which an anvil head forms on many thunderstorms, as they cannot grow any higher. Near the equator, where the ITCZ is, the tropopause is typically in the 50-60,000 foot range, as opposed to 30-40,000 feet typical for the mid latitudes. The high tropopause at these low latitudes means that the storms can grow to great heights leaving little prospect of flying over them.
    The significance of the ITCZ for aviators is that the oceanic thunderstorms within it show up poorly on weather radar. These equatorial storms also tend to produce less lightning than higher latitude storms, which may tend to mask their severity - especially at night. A moonless night and lack of lightning makes it difficult to make a visual evaluation of the storm. For AF447, the half moon was setting in the west, off the aft left of the airplane. The storm tops, by some estimates, towered another four miles above them.
    Studies of storms in this region have shown a weakening of updrafts in the 20,000 foot range, which may account for the lesser amounts of lightning produced. Above approximately 20,000 feet ice crystals form. This shift to a lower energy state of matter (water to ice) gives off a small amount of heat which then adds to the updraft’s upward velocity to reach, and often penetrate, into the stratosphere.
    A meteorological analysis of the flight 447 theorizes that the thunderstorm tops reached 56,000 feet, with updrafts strong enough to penetrate the stratosphere by about 6,000 feet.
    The final accident report states, “The Captain appeared very unresponsive to the concerns expressed by the