August 8, 2011

Happy Monday. Kind of grayish here. Could burn off. It rained yesterday afternoon, but was sunny most of Sat. The fair is in progress, so at the hint of a sun day I am heading over to view the elephants.

We watched a NOVA special on The Crash of Flight 447, the 2009 Air France flight from Rio to Paris that disappeared over the Atlantic. Wreckage was found five days later. Earlier this year they found the black boxes 15,000 feet down. The NOVA special was aired in November 2010, I believe, before the boxes were found, and their team of specialists wrestled with the evidence to determine what happened. Their speculation turned out to be largely correct. The plane headed into a massive thunderstorm at 35,000 feet and its air speed measuring devices, called pitot tubes, froze up. This was at 2:00 am 350 miles out to sea. The Air Bus 330 is fully computerized, but the computer depends on air speed as a critical measurement. When the measurement stopped, the computer issued a series of failure messages that must have scared the heck out of the pilots. What happened next must have scared the heck out of all 228 people on board. The plane stalled (lost lift) and fell out of the sky. The fall lasted about three minutes. The impact with the ocean surface probably killed everyone on board instantly. If not, sinking in 15,000 feet of water did that fairly soon afterward.

The pilots failed to follow protocol and immediately begin flying manually. The NOVA reenactment shows a sweating pilot madly consulting a manual to figure out what was happening. That may not have happened, but in fact the black box records eventually showed that the pilots delayed and then tried a series of ineffective measures. As it happens, Air France was in the process of replacing all the pitot tubes in its fleet because of a series of such failures, and this plane was scheduled for the fix at the time of the crash. A retrospective report showed that in nearly all of these failures, the pilots failed to immediately start flying manually. In those cases just one or two of the three tubes froze up. The outside temp at 35,000 feet is about -40, but extremely pure water vapor can become super-cooled and freeze on contact with an impurity such as a metal tube. There is speculation that the pilots lost their chops watching computers do everything automatically. In addition, the error message screen was positioned directly in front of the pilots, while the manual flight indicators are off to the side, so the repeated warnings may have distracted them from doing the correct things. You can bet that pilot training has been improved since the crash. I sure hope so. The NOVA special is on DVD and I asked the public library to order it. Pretty gripping stuff. Not recommended if you are about to fly.

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