Posted on 11/16/2001 1:15:08 PM PST by kattracks
A major factor in the destruction of American Airlines Flight 587 may prove to be something called flutter — one of the most dreaded bugaboos of flight, experts said yesterda
Flutter is a vibration so violent it can render an aircraft uncontrollable. In tandem with structural flaws, flutter can conceivably rip off a plane's tail.
"Flutter is the demon of all aviation," said Chuck Leonard, a former National Transportation Safety Board investigator. "Once you get flutter, there's going to be damage done."
NTSB investigators probing Monday's crash in the Rockaways said yesterday that they are focusing on the tail section of Flight 587, apparently the first piece of the aircraft to fall off, and the possible effect of turbulence from a Japan Airlines 747 that took off shortly before the American Airlines jet.
Flutter could be the element that connects those two phenomena — though it would be the first time in aviation history, experts said.
"All these things are pretty remote and take pretty unusual circumstances," said Ken Darcy, a former NTSB investigator who is a consultant at Safety Services International, near Seattle. "But obviously, this accident is unprecedented, so we're looking for very unusual things."
Flutter occurs when a piece of an airplane is pushed in one direction, bounces back the other way and then whipsaws violently back and forth.
Something must trigger the problem, and modern jets like the Airbus A300 are carefully balanced and use rigid materials to prevent turbulence and foreign objects from causing flutter.
One or several of those structural and design elements would have had to fail for the wake from the 747 to have caused flutter in the American Airlines jet's tail.
"Turbulence could make the aircraft unstable," Leonard said. "But then there would have to be an anomaly in the vertical stabilizer."
Leonard said the balance is very delicate and that materials designed to prevent the tail from shaking become less stiff over time.
"Even changing the paint surface can change the mass balancing and create flutter potential," he said.
John Hansman, a professor of aeronautics at the Massachusetts Institute of Technology, said the plane's systems could have accentuated the effect of turbulence.
The wake could have caused the yaw damper — an automatic feature that makes constant rudder adjustments for side winds — to start a tail flutter, he said.
"If it did encounter wake vortex, and that got the yaw damper moving, that would do something to the tail," Hansman said.
He said tail flutter was cited as a factor in the 1994 crash of a U.S. Airways flight outside Pittsburgh and in the 1991 crash of a United Airlines jet in Colorado Springs.
In both crashes, tail flutter caused rudders to jam all the way to one side, but the tail did not break off, Hansman said.
Connectors Eyed
Other experts said the tail fin on Flight 587 wouldn't have broken free unless something was wrong with the materials that attached it to the fuselage.
The flanges between the tail fin and the fuselage broke off. Such flanges are made of a composite graphite material that NTSB investigators are closely examining.
Hansman said the composite materials endure fatigue better than metals, but they are more easily damaged by impact. "And they can have internal damage that can't be seen," Hansman said.
Even so, the plane was designed so that one or more flanges could crack and the tail would remain intact.
"You'd be talking about a series of undetected cracks or failures," Darcy said.
Peter Goelz, an aviation consultant and former NTSB managing director, said the pilot might not have even known a piece of the tail had fallen off.
"He's got no rear-view mirror," Goelz said. "All he knows is that he has lost control of his aircraft."
Loss of the tail fin does not necessarily doom a flight. Commercial jets have stayed in the air without one.
In 1985, a Japan Airlines Boeing 747 flew circles between Tokyo and Osaka for 70 minutes after that part of its tail fell off. It finally crashed into a mountain, killing 520 people — the deadliest crash in aviation history.
But, Goelz said, if Flight 587 was in the midst of a massive flutter, "a catastrophic event" was inevitable once the tail fin fell off.
No , terrorism is the true evil of all aviation.
By the way the tail just doesn't fall off a 12 year old plane. (Flutter was probably casued by someone leaving the bolts loose on the tail )
This is an interesting point. Why not wire key surfaces with sensor wires so that any rupture or separation would be recorded on the Flight Data Recorder and displayed instantly in the cockpit?
How could I have been so blind. The answer was right there in front of me.
Silly me. I thought it was terrorism, then the engines, then birds, then wake turbulence, then old damage....
Of course flutter always causes an explosion visible from the ground too.....
And who's accusing whom of stretching to find an explanation?
This is not nearly as far fetched as it may seem.
Just MHO...
A Flutter. ??????????
And best of all ... Maybe the popup ads would go away.
snooker
Here's a definition ; Aerospace Magazine
Flutter is a phenomena which can lead to the catastrophic loss of an aircraft in flight. It needs to be addressed from initial design through flight test and certification. The earlier on in an aircraft program that a potential problem can be discovered, understood, and prevented ("fixed") the less money it will cost to implement the "fix". Fixes can include additional structure (weight penalty), and/or aerodynamic modifications (could result in lower aircraft performance which may lead to more fuel required to perform a mission, etc.).
Presumably, since they have been making these things for nearly 20 years, the appropriate analysis has been done and refined. If an object the size of the rudder "fluttered" sufficently to be ripped offf it would show internal /external damage?
I think it's the paint, probably to cut costs they got it at WalMart and Sam didn't tell them about it's special flutter properties. Maybe all the passengers were followers of Maharishi and doing some Yogic flying casuing synchronised flutter, bad Karma could do this to one of the strongest structures man makes.
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