In 2009, an Air France Flight 447, an A-330, vanished over the mid Atlantic, flying from Rio De Janeiro to Paris. They still don’t really know what happened, since they never found the data recorders. But the folks from NOVA did their own investigation and arrived at some interesting conclusions (SWAGs...?).
ATC stopped receiving pilot reported position reports about the time the plane disappeared from radar, but that didn’t worry anybody at the time, since it’s routine to loose contact with trans-ocean flights in this way. As it happens, at this point the plane was fine, as it continued to send automated data link position reports for some time after radar and comms were lost. In fact it was the ending of the automatic position reports that lead searchers to the small amount of wreckage they eventually found.
But what happened? It seems they went down around the time they flew through a line of thunderstorms. And even though they don’t have the data recorders, the A-330 sends flight control data automatically via satellite to Air France HQ for maintenance purposes. This data shows a series of flight control failures just before the data stopped.
NOVA’s theory is that they encountered “super cooled liquid water” which, when it hit the plane, would have overwhelmed the pitot heat system, resulting is loss of airspeed data, and the subsequent FCS failures. This seems thin. Is there any documented case of this happening before? While there are procedures for flying safely with no airspeed indication, NOVA speculated that if it happened at the same moment the crew slowed down to penetrate the thunderstorm, the highly automated FCS of the A-330 might have caused the crew to be unable to keep up with the changing situation in the dark, leading to a stall. There is, after all, only 20 knots, at 35,000 feet between overspeed and stall. Then the speculation continued that since the A-330 is so automated, that the pilots are “not used to” flying manually, and might have been unable to recover from the stall. I find this difficult to believe. Bottom line is nobody really knows what happened. I sure hope they do some day find the “black boxes”. We can’t have modern air liners just up and vanishing over the empty ocean!
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20 knots separate overspeed from stall in an A-330 at 35,000 feet? Something doesn’t add up here. The NOVA folks showed the pilot, in a sim, dialing back the selected speed from Mach 0.79 to 0.75 while explaining that this is done when entering a thunderstorm. This after they explained to us that there is only 20 knots that separate stall from overspeed. I’m pretty sure Mach 0.75 to 0.79 is more than 20 knots…
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