I Too Found This Puzzling
The other day I was reading an article on the crash of Air France flight 447, discussing recovery of the black box (two years after the crash). It was suspected that the air speed measurement devices may have failed, thus impairing the automatic pilot, but it was not understood why the pilots were unable to fly the plane manually. Was something else going wrong? Did automatic systems, operating off bad data, override manual controls somehow?
The article said that the black box showed the plane went into a stall, and the pilots spent much of the fall pulling back on the yoke to regain altitude. This made zero sense to me. A stall occurs when the wing is angled to steeply. The wing generates lift because the air on top of the wing must follow a longer curve than the air on the bottom of the wing, and thus must move at higher velocity. This higher velocity results in lower pressures. In effect, the plane is sucked up. When the wing is too steeply angled, the air on the top of the wing breaks away from the surface, and lift is lost.
It is therefore absolutely fundamental in stall situations to drop the nose. This does two things -- it decreases the wing angle out of stall territory, and it increases speed, which also increases lift.
Apparently, the experts are just as befuddled as I was reading the data. Dropping the nose in a stall is on the first page of pilot 101. This is not some arcane fact buried on page 876 of the textbook. This is so basic I know it and I don't have a pilots license. But apparently the pilots of 447 were yanking up on the nose through the whole long fall to Earth.
