Posted on 11/16/2001 1:15:07 PM PST by Swordmaker
Tail, Turbulence Emerge As Keys To Flight 587 Disaster
By Sean Broderick/AviationNow.com
14-Nov-2001 10:24 PM U.S. EST
Detailed analysis of American Airlines Flight 587's cockpit voice recorder revealed that both engines were running when pilots lost control, providing the strongest clue yet that something besides an engine failure -- such as an aerodynamic upset, structural failure, or both -- triggered the plane's fatal descent.
National Transportation Safety Board (NTSB) Investigator-In-Charge George Black said that a sound spectrum analysis of the recorder revealed that "the engine signatures extend past the start of the loss-of-control event."
The revelation, made during a Wednesday evening briefing to reporters, all but rules out the possibility than an engine failure brought the plane down, though investigators maintain that all scenarios remain under consideration. As such, both General Electric CF6-80C2s will be flown to American's Tulsa maintenance base for a through teardown.
With the engines apparently cleared and still no sign of terrorism or sabotage, the probe is focusing on the plane's tail and the wake vortex of a Japan Airlines jet that was less than two minutes in front of the American A300-600, information released Wednesday indicates.
Meanwhile, American is inspecting its Airbus A300-600s to make sure there isn't a fleet-wide problem with the planes' tail sections.
A particularly severe wake vortex encounter might explain why Flight 587's tail, found a half-mile from the main wreckage site, was apparently torn away from the fuselage. But such an event without the presence of a contributing factor or two -- like corrosion or some other latent problem with the airplane -- is practically unfathomable, safety officials acknowledged.
In the one previous case in which a tail separated from a jet airliner -- an August 1985 accident involving a JAL 747SR -- a faulty repair left the plane's aft pressure bulkhead weak. The bulkhead ruptured, starting a chain of events that ripped most of the plane's tail away.
Investigators took a closer look at the American A300-600's tail and rudder Wednesday, and found "no evidence of impact with an outside object," NTSB Chairman Marion Blakey said during an afternoon briefing.
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.
Blakey also revealed that the tail and fin, both of which landed in Jamaica Bay to the north of the main crash site, came down almost directly below the point from which the last transponder reading was received from Flight 587. Black cautioned that currents in the bay could have moved the pieces that hit the water, and a more detailed mapping effort would be done to clarify the preliminary data.
Even if the tail pieces shifted somewhat, however, that data points to a rapid vertical descent on the heels of an in-flight event violent enough to rip the tail off of the aircraft.
Investigators know that the Flight 587 pilots reported a "wake encounter" shortly before losing control and are trying to determine how severe the air disturbance may have been.
In a Wednesday afternoon briefing, NTSB released more information about a Japan Airlines (JAL) flight that departed John F. Kennedy Airport just before Flight 587.
More detailed analysis of available data told investigators that Flight 587 started its takeoff roll about 1 minute 45 seconds after JAL Flight 47, a Boeing 747-400 bound for Tokyo Narita began its departure, Blakey said. That's about 25 seconds earlier than the board originally believed, and about 15 seconds sooner than the standard two-minute separation between heavy jets.
Blakey noted that information gleaned thus far did not point to an air traffic controller (ATC) error. "We're not seeing a pattern of an ATC issue," she said. Investigators don't yet know why the two planes were less than two minutes apart on departure, she said.
Flight 587 was delayed by more than an hour, pushing its actual departure time back to about 9:13 a.m. local time. Flight 47's scheduled departure time is 9:10 a.m., and it was right on schedule Monday.
Flight 47 flew and Flight 587, which was headed for Santo Domingo, Dominican Republic, flew similar departures Monday morning. The planes took off on JFK's Runway 31 Left and made sweeping left turns over the bay to southerly headings that lead out over the Atlantic, according to transponder data from the two flights. The 747's flight path was anywhere from 4.3 miles to 5.0 miles west of the A300-600's once each plane was over the bay, and about 800 feet higher than the American jet.
Wind at the time was about 11 knots from 320 degrees, meaning the planes took off almost directly into it, then turned so it was blowing from right to left across their noses.
Combining the data with what's known about wake vortexes -- such as their tendency to fall down and away from the wingtips that create them and move along with prevailing winds -- led investigators to conclude that Monday's scenario "is consistent with a wake vortex encounter" for Flight 587, Blakey said.
With the role of the A300-600's tail growing more prominent by the hour, the investigation is fanning out to cover even more bases. Composite specialists are headed to New York to check out the all-composite A300-600's tail, and American -- after discussions with regulators and safety officials -- decided to check its planes.
"We are not real sure of what happened here," an American spokesman told reporters in New York. "We felt it prudent to go ahead and conduct a test of our Airbus fleet."
The carrier is quickly crafting an action plan, and could not say Wednesday afternoon when or how the checks would be done. But the spokesman said the carrier has no plans to ground any of its 34 remaining A300-600s (similar to the one pictured).
NTSB's Blakey could not say if the checks would be required by other A300 operators. "I think they [operators] are hearing about this at the same time you are," she told reporters. Other U.S.-based A300-600 operators include FedEx and UPS.
Investigators hope to have some help from Flight 587's flight data recorder in the coming days. It was pulled from the wreckage yesterday, but was damaged enough to justify a trip to manufacturer L-3 Communications for some help extracting the raw data.
The mission was successful, and the recorder was back in Washington, D.C. late Wednesday, undergoing analysis at NTSB headquarters. Black said preliminary indications are that the recorder has about 81 hours of "good, clear" data covering 200 to 300 parameters.
This means that the engine sounds continue normally AFTER the event that precipitated the crash began... in other words it was not a loss of an engine that knocked the tail off. But then we had already concluded that. The loss of the tail HAD to be the initiating event. The question then must be asked : did the engines fall off because of the same problem that caused the tail to fall off?
IMPORTANT! The plane actually took off earlier than reported and was only 1 minute 45 seconds behind the Japanese 747! Turbulence to a weakened tail may be the real answer!
You definately heard what they told you.
FYI, Theodore von Karmen was an early fluid dynamicist.
In this reverse von Karmen vortex street, water is accelerated backwards through the vortices. The magnitude of thrust is a function of the mass and acceleration of this backwards moving water.
So the pictures TV showed of a test where the two planes in the test, one behind the other, with the following plane yawing in the wake and turbulence should have had it's tail break off as well? It looked to be a lot less than 4 miles between them. Maybe 2,000 feet.
... And when a plane encounters a bad thunderstorm the tail just falls off?
... And the huricane hunters, why they keep a supply of extra tails back at the hanger to replace the ones which fall off when they fly through a hurricane.
... And in midair refueling better have that spare tail handy. Some toilet paper too. Mid-air tail replacement after refueling?
... sounds a little fishy, errr taily, to me.
Loose bolts anyone? Missing bolts> Cut brackets?
snooker
Seems as if I read somewhere that the Japanese 747 flew for quite some time without the vertical stabilizer.
Ever see a bird without a tail fly. Tough to do.
snooker
Maybe not, but you never know --- Hard to find bolts that were missing after the plane takes off and crashes. Turbulence might just have made it happen sooner, rather than later in the flight. High stress occurs at takeoff/climb out.
snooker
And then there are these to consider:
Crash not seen part of terrorist warning (US Received 11/12 Warning)
Air Authorities Monitored Terrorist Threats After Downing Of Flight 587
The Japanese 747 did in fact fly without the vertical stablizer for quite some time until they ran into a mountain. Also few years back, a B-52 lost 90 per cent of its vertical stabilizer due to turbulence and they were able to land safely.
During refueling in the military we were always up close and personal with aircraft wakes, tails never fell off.
The smooth unbroken structural interface where the tail and fuselage meet is very suspect. If it were fastener failure you would expect a clean break. If the fasteners were missing, then one or more brackets would be undamaged. You can't really tell much from the TV picture, so hopefully NTSB will give real data.
The tail looked undamaged for the most part. Likely first to fall off. Cause, maybe turbulence. But seriously, how many tails have fallen off in the last 30 years or so?
Don't overlook ------ that if someone made 'weakening cuts' in the mounting brackets air turbulence could snap it off and detecting those cuts after a crash could be very hard to do. But with detailed analysis, you should be able to tell.
When you have a bracket mounted structure like a tail, and the structure is under high stress, like a tail is, then any failure(intentional or unintentional) in any one of the brackets could cause the entire structure to fail. Airplanes usually have redundancy built in, so it might take two or more mount failures to be catostropic.
But when I saw the virtually undamaged tail fin pulled from the water, my first thought was hmmm.
If the mounts failed, you would expect the tail to have been ripped off with torn metal obvious on all of the brackets. If tampering was the cause, mounts which were tampered with would show little or no ripped/torn metal.
If all mounts show torn or ripped metal, then external forces(turbulence?) would likely be the cause. Home in on the tail fin brackets, major clue likely there.
One other possibilty is rudder failure for one reason or the other. This has happened before with catastrophic results. But I doubt rudder failure would cause the tail to fail by falling off.
I belive if the tail caused the crash, the NTSB will know what was the exact cause. Wether they tell us right away or not is to be seen.
We'll know soon.
snooker
Repeatedly in 1991, and once again in 1998, sections of rudder came off while the plane was flying 16 km high at twice the speed of sound
My memory is a bit hazy about the 1991 but I seem to remeber there were chunks the size of a garage door that cam off mid - Atlantic and the pilots when they saw it couldn't believe the plane could have flown.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.