Posted on 11/16/2001 1:23:58 PM PST by dead
American Airlines Flight 587 fishtailed violently after being buffeted twice by turbulence from another jet shortly before crashing, the plane's data recorder indicates.
The new data raises the possibility that the crew, responding to turbulence, hit the rudder unusually hard, creating excessive stress on the tail fin that may have contributed to it breaking off.
After the plane twice hit wake turbulence from a Boeing 747, the rudder jerked the Airbus A300-600 sharply left twice, then right. The aircraft then began turning sharply left and diving, probably when the tail fin broke off and the plane went out of control.
The back-and-forth jerking was "very significant", the National Transportation Safety Board chairwoman, Marion Blakey, said. The plane's tail fin and then its engines broke away, causing pilots to lose control.
"We have eight seconds we're going to be looking at in extreme detail," said Tom Haueter, the safety board's deputy director of aviation safety.
The Federal Aviation Administration, with the board's French counterpart, will check all Airbus A300 tails, made almost entirely of a carbon-fibre composite material. Airbus jets are assembled in Toulouse.
The flight data recorder shows the plane passed through one wave of wake turbulence left by a Japan Airlines 747-400 about 48 seconds before the crash, which killed 265 people. The plane responded normally, Ms Blakey said.
Then, about 28 seconds before the crash, the plane passed through another vortex of wake turbulence, the rapidly spinning columns of air that trail from airliners' wingtips.
At first, the A300 responded normally, Ms Blakey said. But then, in the last eight seconds of the data recorder information, the plane began to shift from side to side with a force almost equal to its own weight.
The plane started to bank sharply to the left, with its left wing down, even though the pilot was turning the wheel to the right, the data shows. In the last 2 seconds of the data recorder, the information from the rudder was "unreliable," the NTSB said, meaning it was possibly no longer attached to the plane.
Investigators have seen no evidence suggesting sabotage.
American Airlines, with 34 A300s, is the only US airline flying the model.
Wake turbulence has never been known to have knocked a tail fin off an aircraft, and some experts say the structure might have been flawed or weakened. The same American Airlines plane encountered "severe clear air turbulence," in 1994, FAA records show.
The plane dived 35,000 feet without warning over the island of Martinique. People and food trolleys hit the ceiling, and 47 of the 221 people on board were injured.
Michael Hunt, an aerospace structural engineer in Savannah, said composites are increasingly popular among aircraft builders because the materials are lighter, stronger, more durable and easier to mould into complex shapes than metal.
But composites also hide damage and manufacturing defects and give no outward indications of stress before to failure.
"It's an all or nothing material," Mr Hunt said.
Michael Hunt, an aerospace structural engineer in Savannah, said composites are increasingly popular among aircraft builders because the materials are lighter, stronger, more durable and easier to mould into complex shapes than metal.
Mike Hunt said this? I wonder what Heywood Jablomy thinks.
I have not seen any comments from the French or Airbus consortium on these theories. Has anyone else? They surely would speak out in defense of their aircraft if the theories being proposed are not justified by their data?
Specifically, the "Double Rudder-Kick Test". The test pilot stomps one rudder pedal down as hard as he can, then briefly kicks the other rudder pedal as hard and as fast as he can, then the original pedal hard and fast.
Sometimes they wear parachutes when running this test.
If the vertical stabilizer fell off from wake turbulence or excessive rudder activity, it was defective.
Let me rephrase that. "...defective" is self-evident. "Previously Damaged" would be more appropriate.
The November 14th update from Aviation Week website indicated that that aircraft had a delamination in the composite structure during manufacture and was repaired with doublers and rivets (standard practice)and then delivered to AA with the documentation but with no recommendations for additional inspections or maintenance.
Sorry I don't have the link, I read it at work.
P.S. The reply link to AMDG&BVMH didn't work. I had to reenter the TO: name. I think its the "&".
Investigators are a long way from determining precisely why Flight 587, an Airbus A300-600, went down shortly after takeoff Monday, but so far, all indications are that the separation of the plane's tail played a key role. Six attachment fittings that hold the tail to the plane's fuselage apparently came free, meaning either something caused the pins that secure the fittings to break, or the fittings themselves failed. Nothing hit the tail, investigators said, meaning it broke away for some other reason.
Investigators are looking into evidence that one of the fittings was damaged before Airbus delivered the plane to American in 1988. An examination of maintenance records at the airline's Tulsa base turned up the information yesterday.
Meanwhile, in Tulsa, the maintenance records group discovered that one of the six main attachments that held the Flight 587 plane's tail to the fuselage underwent a significant repair in 1988, soon after the plane rolled off the assembly line but before it was delivered to American.
The left-center fitting "delaminated," and technicians in Toulouse, France, where the plane was built, added a "doubler" and rivets to reinforce the joint, Black said at the evening briefing. Airbus then delivered the plane to American but did not indicate that special inspections of the repaired area were necessary.
The attachments are to be checked every five years, Black said. The last check of the American A300-600's tail/fuselage attachment fittings took place in December, 1999, which is also when the plane had its last heavy maintenance visit.
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