FAA knew of problem with tail of Airbus
By PETER CHENEY
From Saturday's Globe and Mail
A safety warning affecting the tail section of Airbus A-300 jetliners was scheduled to take effect one day after the crash of American Airlines Flight 587, which plunged out of control Monday after its vertical tail apparently ripped off in flight.
The warning, known as an airworthiness directive, points out a serious safety problem that could leave the pilot without rudder control, making it difficult, if not impossible, to guide the airliner.
The American Airlines jet that crashed after takeoff in New York was an Airbus A-300 Model B4 manufactured in 1988. It was among those that the warning affects.
The U.S. Federal Aviation Authority first published the airworthiness directive on Oct. 29. It was scheduled to take effect Tuesday, forcing all A-300 operators to inspect key rudder-system components.
Investigators of Monday's crash have not drawn any conclusions, but it is increasingly clear they believe the tail section played a key role.
An aircraft structural engineer familiar with the A-300 said problems with the rudder system could have led to a cascading series of failures, with the jet's vertical fin separating from the airliner.
The FAA issued the warning after French aviation authorities alerted them to problems discovered in at least two other Airbus A-300s.
It warns that corrosion of components known as spring boxes could lead to an emergency, and reads:
"Since an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design . . . this AD is being issued to prevent failure of both spring boxes of the variable lever arm (VLA) due to corrosion damage, which could result in jammed rudder pedals, loss of rudder control, and consequent reduced controllability of the airplane."
On Thursday, the U.S. National Transportation Safety Board issued a new directive that calls for the inspection of the tail assemblies on Airbus Model A300 airplanes, operated by 27 airlines around the world. The directive warns of possible "loss of the vertical stabilizer and/or rudder and consequent loss of control of the airplane."
It calls for a detailed inspection of a long list of components, including the fittings that attach the fin to the airframe, rudder-hinge fittings, rudder-hinge arms, support fittings for all rudder hinges, and rudder-actuator support fittings.
The role of the rudder in the crash of Flight 587 has been a topic of intense discussion among investigators probing the crash, which killed 260 people aboard the plane and several others on the ground.
The jet broke apart in flight less than three minutes after taking off from New York's John F. Kennedy International Airport, raining jet fuel and flaming wreckage on the Rockaway neighbourhood in Queens.
Investigators increasingly believe the crash was caused by an unprecedented structural failure of the jet's vertical tail which was found in the waters of Jamaica Bay, several kilometers from the rest of the wreckage. Aviation experts believe the jet went out of control after the fin ripped off, shedding parts and spinning toward the Earth as the pilots fought helplessly for control.
Digital information recovered from the doomed jet's flight-data recorder shows Flight 587 encountered wake turbulence from a Japan Airlines 747 that had taken off just ahead of it. There has been extensive speculation that the Airbus may have broken apart after hitting the other jet's wake.
But aviation experts dismiss that idea, pointing out that airliners are designed to withstand forces many times higher than those that could be experienced in wake turbulence.
Instead, they believe the wake turbulence exposed a fatal flaw in the jet's structure or control systems.
"An intact airliner would never come apart in wake turbulence," said an aircraft structural engineer who worked on the certification of the A-300 when it was first introduced to the North American market. "But if there was something wrong, it would magnify it."
The engineer said problems with the rudder system could have led to a series of failures as the aircraft encountered the swirling air of the other jet's wake. He believes the rudder may have torn away as the pilots fought to overcome binding in the system, changing the aerodynamic configuration of the tail and subjecting the fin to massive and unanticipated loads.
Flight-data recorder information released by the NTSB portrays a disastrous scenario consistent with this postulation.
After hitting the wake of the plane ahead of it, the Airbus began a series of oscillations, yawing from left to right, then back again. Seconds later, the data stream from the Airbus's rudder "became unreliable," in the words of NTSB investigators, indicating a serious malfunction of some kind.
The jet then began rolling to its left side as the pilots fought helplessly to compensate. Before it stopped working, the flight-data recorder shows the Airbus rolled 25 degrees to the left, even though the pilots applied full-right roll control. The recorder also shows the jet dropped into a 30-degree dive, and began revolving rapidly toward the left.