Posted on 11/24/2001 5:35:14 PM PST by Swordmaker
"The board [NTSB] confirmed that Flight 593's thrust reversers were stowed, the flaps were apparently retracted, and the landing gear was up when the plane went down."
In the previous 24 hours the plane underwent a low class maintenance inspection, I believe. Would the lines have been cut then? Would hydraulic fluid have been leaking from the plane when it was parked in front of the terminal? Why didn't the pilot see the leak in his walk around?
Maybe the terrorist got lucky...Could be that is was only known that the plane would drop out of the sky somewhere between the beginning and the end of the flight, depending on how quickly or slowly the oil leaked out...I'd like to see a schematic of the hydraulic system...
The checks, mandated for U.S. and French carriers under directives issued in those two countries Friday, were deemed necessary once investigators determined that the American aircraft's tail separated along an attachment point. About 20% of the world's 410-odd affected aircraft have been checked, and no carrier has reported anything unusual, sources tell AviationNow.com."
Problem here is after the NTSB investigated the crash site, who investigated the NTSB????
As I have also pointed out, there are a number of cases where these large airliners have been returned to landing after losing their vertical stabilizer--the fact the stab was gone would not be expected to have caused the airplane to fall out of the sky either.
"This is way beyond my expertise. But the statement about the B-2 fly-by-wire requiring no vertical tail doesn't prove a thing. There's nothing resembling that kind of special computer controls in an Airbus." Cicero, you are wrong. To the contrary, the Airbus is a pure fly by computer airplane. And in fact, that should not make any difference either--unless the pilots made serious errors which do not appear in the record, if they could have hand flown the airplane, loss of the vertical stab would not have kept them from returning to make a safe landing. The pilots were dependant on a computer driven control system to fly the airplane--although most of the new commercial airliners are fly by wire airplanes (electrical inputs to a computer run the control surfaces), the Airbus is the most dependant on the electrical computer system.
"I, too, thought that was a bit off the wall... the B1 and B2 will NOT fly without computer assistance because of their inherent instability." (From Swordmaker)
Sure but so what--there are other airplanes out there that also do not have vertical stabilizers and which have no computer or electrical servo driven flying systems either--the Bonanza V34 is one example. Loss of the vertical stab did not have anything to do with this event either.
The author here advances an analysis that would account for the accident--uncommanded deployment of the thrust reverser. He accounts for the event by sabotage. Well and good--that is a possibility. "How easy this author makes it seem for someone to clip a few critical wires within an engine, making cuts that bring down an airliner without fail. I wonder how the delayed flight of this airliner fits into this scenario?" (By Republic) No. His suggestion is a little more complicated than that--his sabotaur was not cutting wires, he was cutting hydraulic tubeing which is a little more difficult and requires a fair amount of knowledge because there are a number of metal tubes up there and if you cut the wrong one, the fan simply does not spin. But his thesis is possible although I think remote. Your point about the late departure is however relevant--by the time they were off the ground, they would have run out of the sabotaur's time line which makes the authors suggestion a little less likely.
For one thing, no reason an uncommanded thrust reverser event requires sabotage--it happens more often than the flying public wants to know for a whole host of reasons other than sabotage. One of the Boeing airplanes had a reputation for regular uncommanded deployments because of some glitch in the way the systems were wired.
The pilot is trained to recognize the problem and the usual remedy ought to have been to cut power to the engine. Even if the pilots screwed up and failed to recognize the problem, they still had to make a number of other mistakes to get this result--it is possible but in my view remote. Further, if it happened that way, the NTSB would have jumped on it because they could have said it happened by accident. So I tend to doubt the evidence will support this series of events.
My own view is that there is much more likely series of events that explains the crash and those events start with an incendary device in the checked baggage compartment. That explanation also deals with another piece of evidence which is the reliable eyewitness testimony to fire at the root of the wings on both sides of the airplane.
Do you know and, if yes, will you list the URL for the website displayed behind TV newscastes which displays all the flights in the air at that time. It was widely used on 9-11 as the planes were being grounded. Perhaps you saw it and know it.
Should another reader have the URL, please post it as a ping to me.
It seems to display flight's locations, superimposed on a regional map of the country, with light blue arrows showing the direction and the flight number, with possibly more information.
I have looked but could not find it. The fellow on MSNBC never responded to my email request, either.
Many thanks, in advance.
The thrust reverser is driven by an air motor powered with pneudraulic (air) pressure drawn from a bleed air duct off the compressor. Connection between the air motor and the reverser cowls is accomplished with the use of flexshafts (flexible drive shafts).
The next morning about an hour after the jet engines were started, the hydraulic fluid now under pressure would drip from the cut line until none was left in the line and the thrust reverser would simply slowly drift into the full on condition while in flight and a catastrophic crash would occur only seconds later.
Hydraulic fluid under pressure wouldn't drip from a cut or severed line. It would fly out of there, rather like a severed artery. Any falling onto the hot section would cause a massive amount of smoke to come from the engine, enough that the ground start crew would stop the startup procedure. If it leaked out overnight, then it would have leaked through the cowling as well, and left a puddle on the ground.
With regards to the thrust reverser cowl "simply slowly" drifting into the full on condition. It would have to be driven into position by the flexshafts. At full power, depending on the model, the CF6 puts out between 40,000 and 72,000 pounds of thrust. Reverser cowls are driven into place and held there...because that much thrust will just blow them open.
Now we move into the realm of science fiction, or even fantasy. Suppose that there is a teleportation device, carried back to us by time travelers, to inject these mysterious occurrences into our everyday lives, at a time in history where there was great turmoil about bacteriological agents, and terrorist attacks using airliners. A small piece of a structural part on the tail surface of the airliner was teleported away, so it looked like a stress failure, and a small quantity of anthrax spores were teleported into the woman's nasal passages.
But of course there shall be developed much more rational explanations, for each of these seemingly unrelated events. Just keep in mind, that not all the frontiers have yet been explored, or even defined very well so far.
1.Thrust reversers are normally stowed in a mechanically locked position, so that in case of a hydraulic system failure they remain closed.
2.Hydraulic pumps are mechanically driven by the engine during and after engine start. A "cut" hydraulic line would spew tremendous amounts of fluid while under pressure at 3000 psi and trigger a cockpit warning light. Hydraulics power all major aircraft systems including brakes and nose-wheel steering. I doubt Flight 587 would even have been able to taxi to the runway for takeoff had this "cut line" scenario occurred.
1. Easily;
2, Separately;
3. Consecutively.
4. The vertical fin and rudder, at the most critical stage of flight, failed due [Probably] to the acculmination of a series of small errors, break downs and failures which may or may not eventually include such contributing factors as bad design, material failure, fatigued components, previous maintenance damage -- etceteras;
When the Vertical fin failed at that potentially most unstable stage of flight -- and especially when bearing in mind that it did not leave cleanly and most certainly caused the aircraft to yaw violently -- all "yaw-damping" control was lost.
Once the aircraft began yawing under take-off and then increased to the "maximum power" setting the pilot [It was the F/O's leg, he handled the controls] called for, the potential that an assemetric thrust condition existed and/or was caused increased.
Once that happened it was only milliseconds before the gyroscopic effect of violent yawing on turbine rotors spinning in excess of 10,000 RPM caused the engines to be ripped from mounts not designed to handle such incredible forces applied to them at 90 degrees around the engines plane of rotation.
The forces were such it was as iff a giant hand had grabbed hold of the engines on a childs model an simply twisted them off.
Cutting hydraulic lines before the engine is started guarantees a hydraulic fluid gusher that would be easily discerned before takeoff - it would take just a few seconds to gush ALL aircraft hydraulic fluid onto the runway - it works at 3000 psi.
All thrust reversers are manufactured and fitted with a system of locks and feedback mechanisms. Lock failures show up on the cockpit instruments, and having a red light on will prevent the flight from occurring. The feedback mechanism detects a thrust reverser starting to deploy, and then sends the hydraulic fluid to stow the reverser before it can deploy. If they can't fix the T/R system on the ground, then they put a pin in the reverser structure to prevent commanded or uncommanded deployment.
After the Air Lauda crash in Thailand, caused by a T/R inadvertently deploying, all aircraft makers had to declare their aircraft either reliable or controllable. The big twins like the A300 are not controllable with a T/R deployed, so they had to go the reliability route and install a better safety system with 3 redundant locks. There was a deadline to do it, which has passed, I think. Therefore, it's highly likely that this aircraft had the redundant system installed.
The author is correct that an in-flight T/R deployment would cause the aircraft to fly approximately the way it did. It was the first comment in my office after the crash - it may be a T/R deployment. But the statements from the NTSB make it clear that the T/R's were not the cause.
I've previously offered two probable causes to this crash - a rudder partially breaking loose from the vertical tail, causing high static and dynamic loads before it departs the aircraft; or a latent structural defect in the vertical tail skins that was excited by either the wake turbulence or anomalous rudder operations.
As I've stated before, I am an aerospace engineer at a company that makes engine nacelles, including thrust reversers.
The fan duct lines in the CF6-80C2 create pressure forces such that the thrust reverser should remain stowed (and not drift back) during high power flight.
If the reverser was the cause, we would have heard about it already. An earlier poster noted that the NTSB stated the T/R's had not deployed. [but then some folks don't believe the NTSB or other alphabet agencies!].
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