Rudder Shifts Can Spell Doom, Pilots Warned
Federal officials said Friday they have uncovered a new aviation safety problem that under rare circumstances could cause any jetliner’s tail to break off.
The National Transportation Safety Board urged immediate changes in training procedures to warn pilots against making sharp, back-and-forth rudder movements that could put an excessive strain on a plane’s vertical tail fin.
“We have calculated that certain rudder-movement inputs by pilots could cause a catastrophic failure of an airliner’s vertical tail fin,” said NTSB Chairwoman Marion C. Blakey. “This concern is not limited to the A300, or even to Airbus models. Our concern is industry-wide.”
The Federal Aviation Administration, which sets safety standards for the industry, said it would quickly comply with the NTSB advisory. “We agree with the safety intent and the substance of the recommendation,” said spokesman Les Dorr.
The warning arises out of the safety board’s investigation of the crash of American Airlines Flight 587 in November, shortly after takeoff from New York’s John F. Kennedy International Airport. The tail fin of the A300 jet tore off, making the plane unflyable. The crash killed all 260 people aboard and five on the ground.
The cause of that accident--and indeed, whether pilot actions played any role--has yet to be determined. The NTSB is also investigating possible flaws in the composite material used to build the 27-foot-long tail fin.
Blakey said the board’s analysis and simulations went beyond the crash of Flight 587, revealing a potential safety problem that could affect about 15,000 jetliners flying around the globe.
Pilots questioned the NTSB’s recommendation. They say they usually avoid making sharp rudder movements the way the driver of a sport-utility vehicle would avoid spinning the steering wheel back and forth on the freeway.
“To apply full rudder in opposite directions in rapid succession is something that a pilot would not do,” said Barry Schiff, a retired airline captain and safety consultant.
Industry officials said the condition described by the agency is so rare that it is hard to draw any immediate conclusions.
In more than 300 million flights by modern jetliners, there has been no case of a tail snapping off because of rudder movements initiated by pilots.
“The NTSB has identified an important issue here in terms of pilot awareness of how their airplanes behave,” said Rich Breuhaus, chief aviation safety investigator for Boeing Co. “But it would be unfortunate if the recommendation was misconstrued that there was somehow a serious problem with the world’s airplanes. The service history of these airplanes stands up pretty darn well.”
Airbus spokeswoman Mary Anne Greczyn said the company will immediately revise its training manuals to reflect the NTSB recommendation. “Temporary revisions to all our flight manuals will be in place Monday,” Greczyn said.
Blakey said the NTSB is not trying to alarm travelers and has reached no conclusions about the cause of the Flight 587 crash.
“Our purpose is not to create unnecessary concern but to notify pilots that we have learned something that requires their immediate awareness and to ultimately prevent such an event from happening in the first place,” she said.
“It is very important that we all clearly understand that this recommendation is about pilot training and education, and is not a question of pilot error,” she added.
The NTSB is studying whether the federal safety standards that govern design of major aircraft components like the tail fin need to be revised in light of its findings. The current standards do not address the issue of back-and-forth rudder movements because pilots don’t normally engage in such maneuvers.
Asked if the standards should be revised, Blakey said: “We’re not there yet.” Such a revision could entail expensive retrofitting of thousands of aircraft.
The rudder is a movable panel on the rear edge of a plane’s tail fin that helps keep it flying straight. Unlike a ship’s rudder, it does not play a major role in turning the aircraft, which is accomplished by moving panels on the wings called ailerons.
In aviation, the rudder is chiefly used to keep an aircraft on course when landing or taking off in a crosswind, or if an engine fails. The safety board said it did not find any problem with continuing to use the rudder in these conditions.
Pilots employ pedals to operate the rudder. And to prevent over-stressing the tail fin, jetliners are fitted with a device that limits rudder movement during high-speed flight.
The NTSB said Friday that Flight 587 experienced five sharp rudder movements in opposing directions in the last seven seconds of its flight. In each case the rudder moved close to its full allowed limit of about 9 degrees. It is not clear whether those motions resulted from pilot commands, a rudder malfunction, a weakened tail fin starting to come off or some combination of factors.
A safety board investigator said the agency has studied more than 20 “rudder oscillation” incidents on jetliners but “none of them directly relate to our problem.”
The NTSB said pilots should be aware that at higher speeds, relatively light pressure on the control pedals can result in sharp rudder movements on some planes. They cited the A300 and the Boeing 737 as examples.
In the aftermath of the Sept. 11 terrorist attacks, Blakey said the safety board is also concerned that pilots may misuse the rudder in taking emergency action to thwart a hijacking. But Dorr, the FAA spokesman, said the agency has not authorized pilots to undertake acrobatic maneuvers.
“The only situation in which we would approve of aggressive maneuvers would be in cases where the procedures are included in the flight manual and are part of the pilot training program,” Dorr said.
