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Date Posted: 14:42:58 01/02/02 Wed
Author: Washington Post
Subject: The Airbus A300

By Don Phillips
Washington Post Staff Writer
Wednesday, January 2, 2002; Page A04


The Airbus A300 that lost its vertical tail fin and crashed into a New York neighborhood Nov. 12 had been blown backward onto its tail in 1987 by a violent storm that swept the Airbus factory in France as the wide-body plane sat outside awaiting completion, said sources close to the investigation.

There is no indication that the freak event had anything to do with the crash of American Airlines Flight 587, which killed 260 people on the New York-Santo Domingo flight and five on the ground. Airbus sources said the aircraft was carefully inspected after the storm and no damage was found.

But investigators said they cannot overlook potential evidence, no matter how old or remote, in a crash that has defied explanation and may take investigators into unknown territory.

National Transportation Safety Board investigators, Airbus sources and French authorities shy away from calling the disaster a "mystery crash," particularly because they have gathered useful information from the crash site and from the plane's flight data recorder and cockpit voice recorder. Investigators know a lot about what happened but cannot say why it happened.

No one found any indication of terrorism. The engines checked out fine. Weather does not seem to have been a factor. But almost everything else remains on the table and many months may pass before investigators can confidently identify a probable cause.

All the major possible scenarios -- serious errors by an experienced crew, a heretofore unknown type of rudder malfunction, an unlikely flaw in the composite carbon-plastic tail fin attachments, hidden damage that eluded inspectors, or some combination -- are disturbing.

The American Airlines flight left John F. Kennedy Airport in beautiful weather the morning of Nov. 12, taking off to the west and turning gently to the south over Jamaica Bay. Everything seemed normal.

Less than two minutes into the flight, the plane was apparently hit twice by wake turbulence flowing from the wingtips of a Japan Airlines Boeing 747 flying several miles ahead. The wake, two whirling columns of air that are a normal part of flying, was enough to get the crew's attention and perhaps surprise passengers. But preliminary readings from the flight data recorder measure it at only 0.1 times the force of gravity, hardly enough to seriously affect a plane as big as the A300.

Within a second after the second wake encounter, however, the plane began a series of violent fishtail movements. The rudder, the hinged plate at the end of the vertical tail fin, whipped from side to side at least five times. The ailerons, plates on the wing that control rolls and turns, also repeatedly moved abruptly.

The vertical tail fin -- usually called the vertical stabilizer -- cracked off when the composite material above the attachments failed.

As the plane gyrated through the air, both engines were torn loose, one landing in the back yard of a home and the other in front of a service station. The fuselage and wings of the A300 did a belly-flop into a neighborhood of neatly kept homes.

Investigators are reasonably certain they know the sequence of events that led to the crash. But why did the rudder begin its sharp movements? And why did the vertical stabilizer crack loose?

Whatever happened in those last few seconds left the crew dumbfounded. The transcript of the cockpit voice recorder is being closely held, as usual, but investigators have described the crew's mood as "panic."

The rudder is seldom used by crew members unless they need to steady the plane after an engine quits. It is sometimes used during landing or takeoff. An automatic device called a yaw damper makes small rudder movements in flight to prevent "Dutch roll" -- the typical fishtailing as a swept-wing commercial jet comes out of turns -- or to steady the plane in turbulence.

Yet investigative sources now generally agree that sharp rudder movements began the crash sequence.

That is one reason investigators are paying particular attention to any record of damage or maintenance to the tail section. They determined early in the investigation that before the aircraft left New York, it experienced a malfunction of its yaw damper and its "pitch trim," which moves the horizontal stabilizer to keep the plane level. A mechanic reset the computer that controls both tail-mounted mechanisms and they operated normally, the safety board reported.

Then days ago, investigative sources said, an American Airlines pilot assigned to the investigation remembered he was training at the Airbus factory in Toulouse when a storm blew the same aircraft back on its tail. Sources said his memory proved correct.

Sources said the plane was almost complete but its engines were not attached to the wing. Without the heavy engines, the plane was tail-heavy. It was sitting outside the factory when the storm hit and it tipped back on its tail. How hard it hit is uncertain.

An Airbus source said the company inspected the plane thoroughly and found no damage, including in the tail section.

"I'd be surprised if this had anything to do with the crash," the source said.

The rudder and the vertical tail fin were found in Jamaica Bay. The tail fin was undamaged other than at its attachments, but the rudder was torn into several pieces.

Determining why the rudder was in pieces -- two main pieces and several smaller ones -- is a key part of the investigation. One possibility is "flutter," in which a flight surface such as the rudder begins vibrating and oscillating wildly, tearing itself apart almost instantaneously.

Flutter is a well-known aviation killer. Manufacturers and regulators such as the Federal Aviation Administration go to great lengths to ensure flutter is not possible in almost any conceivable scenario on any commercial aircraft.

Investigators know the rudder and its control pedals in the cockpit moved in tandem. But much interpretation of the flight data recorder will be necessary to determine whether the pilots pushed the pedals or the rudder somehow moved on its own, back-driving the pedals.

If the pilots pushed the pedals, then investigators would be dealing with a scenario in which experienced pilots badly mishandled their plane and overstressed the vertical tail fin. If the rudder moved first, then investigators must determine whether they have found some new failure in the rudder control mechanism or the computer that controls it.

Another, potentially more important question is why the vertical stabilizer tore off. Composite material is made to be stronger than metal; there is no record of any other Airbus tail fin being torn off in flight. It is possible that the plane's gyrations stressed the fin beyond its ultimate design limit or that some flaw was present in the composites.

Preliminary calculations, sources said, indicate the tail fin may well have been overstressed. But sources close to the investigation said it is far too early to make that determination.

What concerns investigators is that the crash of Flight 587 is the first involving composites in a key load-bearing role. Both the stabilizer and rudder have been shipped to NASA Langley Research Center in Hampton, Va. Because of the importance of the composites to the future of aviation, investigators will first spend weeks working up a test protocol. They will then perform almost every possible type of nondestructive test before moving to destructive testing.

Another issue that will stretch the investigation is the complexity of the digital flight data recorder. The Airbus recorder, with more than 200 measurements, is a dream for the safety board but also extremely complex to decipher and interpret.

A senior investigator said that normally at this point, an investigation would be coming together toward a solution. This one is still expanding.

"It hasn't started coming back together yet," he said. "We just don't have the tangibles yet."


© 2002 The Washington Post Company

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