ORAC posted the following link in the earlier thread about AA pilots seeking to have the A300 grounded.
<a href="http://pull.xmr3.com/p/25356-E59F/30254611/rudder.html" target="_blank">http://pull.xmr3.com/p/25356-E59F/30254611/rudder.html</a>
This is AviationWeeks technical analysis article (with graphs) on how excessive rudder movement can overstress the fin. This article is cited in the NY Times story of Feb 9, below, and was also cited in a USA Today article earlier this week:
"WASHINGTON, Feb. 8 - The inquiry into the crash of an American Airlines plane in Queens three months ago has shown that a passenger jet can break up in flight if the rudder suddenly flips back and forth, investigators said today.
"Pilots should be trained that such a breakup can occur even at the low speeds that rudder movements had previously been considered safe, the investigators added.
"Government rules on how strong an airplane's tail must be do not take into account sudden back-and-forth rudder movements like those that occurred in the last moments of American Airlines Flight 587, the National Transportation Safety Board said.
"In fact, the board said, in some cases a fairly light tap on the rudder pedals may be enough to cause structural damage. If the pilot reverses the rudder just as the plane reaches its limit in one direction, investigators said, the movement can overload the tail, which they say may have. .happened to Flight 587.
""It is possible, particularly with reverse action, to do catastrophic damage to the tail assembly," said Marion C. Blakey, the board chairwoman.
"In an unusual response, the Federal Aviation Administration immediately said that it agreed with the substance of the recommendation and would make a formal answer shortly. The. .safety board recommendations are advisory; the F.A.A. sets pilot training requirements.
"The recommendation is in contrast to a text jointly developed by Airbus, Boeing and major airlines on recovering from aircraft "upsets." That training tool, as the safety board pointed out today, stresses that "pilots must be prepared to use full control authority when necessary."
"The board said that the problem might extend to all big jets, not just Airbuses, and not just those with tails made of composites, as the tail on the A-300 is. The board, which based its recommendation on calculations of side stresses that would have been produced by the plane that. .crashed and the rudder movements that were recorded, is still trying to determine whether there was a pre- existing weakness in the tail. The board is also continuing to investigate whether the rudder moved because the pilots. .pushed the pedals, or whether it moved because of a mechanical malfunction.
""Even if investigators determine that the rudder moved in response to "pilot inputs," as engineers call it, Ms. Blakey stressed, "this tecommendation is about pilot education and training; it is not about pilot error."
"But it is also about the standards used to certify the airplane as safe to fly. Those standards, used by both the F.A.A. and, in the case of the Airbus, its European counterpart, are taken by pilots to mean that a safety system called a rudder limiter will prevent them from. .overstressing the tail.
"In normal flight, using the rudder will turn the nose of the plane out of line with its direction of travel, like a car skidding on an icy road that points to the side without changing direction. In the air, it is called a yaw. In a. .big airplane, in which the tail is 100 feet or more behind the center of gravity, a yaw can produce large pressures on the vertical tail.
"The rudder limiter on the A-300 and many similar planes blocks the rudder from moving too far and creating a dangerous yaw. The faster the plane flies, the closer the limiter holds the rudder to the neutral position. Aircraft builders calculate the maximum force that the yaw can produce and design the plane to survive 50 percent more.
"If the rudder is pushed to its limit, the plane will swing hard, and because of its momentum, will reach maximum yaw and then settle back slightly toward straight, in a new equilibrium.
"The problem is that the certification test assumes that when the plane reaches maximum yaw, the rudder is held steady or returned to neutral position, and that the rudder is not pushed in the opposite direction until the plane has. .reached equilibrium. In the case of the Queens crash, the rudder appears to have moved in the opposite direction at the moment of maximum yaw, and that may have overstressed the tail.
"That possibility was first raised publicly by Aviation Week & Space Technology magazine on Jan. 21, after it conducted its own analysis.
"This was news to many pilots. "The traditional wisdom is that the rudder limiter will prevent you from exceeding the certification limit," said a senior captain at another airline who has trained scores of pilots on using the rudder.
"But the captain, who did not want to be further identified added, "there are no maneuvers we teach at all that would require you to use full rudder in one direction, then another direction.""