In yesterday's Wall Street Journal, J. Lynn Lunsford and Andy Pasztor reported that investigators looking into the Colgan commuter-plane crash in Buffalo were beginning to think that the pilots' handling of the situation, rather than the intrinsic perils of "airframe icing" conditions, may have been the immediate cause of the tragedy. (Previously here; also, valuable posts here by Miles O'Brien and here by Patrick "Ask the Pilot" Smith of Salon.) The WSJ article, titled "Pilot Action May Have Led to Crash," quoted unnamed "people familiar with the situation" to this effect:
The commuter plane slowed to an unsafe speed as it approached the airport, causing an automatic stall warning, these people said. The pilot pulled back sharply on the plane's controls and added power instead of following the proper procedure of pushing forward to lower the plane's nose to regain speed, they said. He held the controls there, locking the airplane into a deadly stall, they added.
With all the usual caveats -- that it can take months or years to find out the real cause of airplane disasters, that sometimes the real cause is never known, that these unnamed sources might prove to be wrong, etc -- here is why this information could be significant. What follows is an Aerodynamics 101 explanation that would be obvious to people in the flying world but perhaps not so evident to the general reading public:
"Stall" is a very important word in aviation, but it means something entirely different from what most readers (or passengers) would assume. It has nothing to do with the operation of the power plant. That is, an airplane stall has nothing in common with an automotive stall. A car stalls when something goes wrong with the engine. An airplane stalls when something goes wrong with the flow of air over the wings. When birds flew into both engines of a USAir jet last month, the engines lost power and stopped -- but the airplane didn't "stall."
The crucial point about aerodynamic stalls is that they occur when the wing's "angle of attack" into the air is too high. That is, the wing is angled so sharply into the oncoming wind that the air can no longer flow smoothly over the wing's top surface to generate lift. When the wings stop generating lift, the airplane becomes dead weight and falls right out of the sky.* A Wikipedia primer on the whole topic is here; a passage on "How a Wing is Flown" from Wolfgang Langewiesche's unsurpassed 1944 classic on airmanship, Stick and Rudder, can be found here, via Google Books. (Yes, Wolfgang L. was the father of William Langewiesche, now of Vanity Fair but for many years my Atlantic colleague and flying mentor.)
For the pilot of any airplane, large or small, the practical implications of a stall center on whether you are pulling the airplane's nose up (by pulling the control wheel or stick backwards, toward your body) or pushing the nose down (by pushing the stick forward, away from you). Everyone who has ever flown an airplane has gone through stall-recovery drills. These involve climbing to a safe altitude; pulling the stick back more and more until you raise the nose so high and make the angle of attack so great that the airplane stalls and begins falling toward the earth; and then immediately pushing the stick forward as the very first step in getting the airplane under control and flying again.