The November 2001 crash, shortly after takeoff from JFK, of American Airlines Flight 587 sent a tremor through the aviation community. It involved an extremely rare event: the structural failure, and complete separation, of one of the major flying surfaces-namely, the vertical stabilizer-of the airplane, an Airbus A300-600. In the ensuing loss of control, the engines also broke away from the airplane, which crashed on Long Island killing all 265 persons aboard.
According to the National Transportation Safety Board's recently published report on the accident, only one other commercial airliner, a Boeing 707 that broke apart in severe turbulence near Mt. Fuji in 1966, has ever lost a fin in flight from external causes. That 707 encountered mountain wave turbulence so violent that the airplane broke into a number of pieces before reaching the ground, and a U.S. Navy aircraft sent to investigate encountered gust accelerations far outside the flight envelope of any airliner. In the case of the Airbus, however, extreme turbulence was not a factor. The closest thing to it was the wake of a 747 five miles distant. Such a wake can give even a large airliner a pretty good thump, but cannot tear it apart.
The finding of the NTSB was that the first officer, who was the pilot flying, used inappropriately vigorous, rapidly alternating rudder inputs in response to the wake encounter. Normally, jet pilots stay off the rudders; but this particular pilot, according to one captain who had flown with him, had shown an inclination to overuse them. (On the other hand, some described him as an above-average pilot who never flew airplanes aggressively, but rather "smoothly and accurately.")
Two other factors were thought to have contributed to the overcontrol. One was the design of the A300-600's rudder control system, which provided very little force feedback. In fact, the additional force needed to drive a pedal to its stop at 250 knots is less than the 22-lb breakout force-intended to prevent inadvertent rudder movements-needed to move the pedal in the first place. A survey of airline airplanes found none with rudder forces lower than those of the A300. Most other Airbus models, however, including the big four-engine A340, have characteristics similar to those of the A300-600, while Boeing and McDonnell-Douglas models without exception have lower breakout forces and considerably higher deflection forces.
