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AA 587 -- Vertical stabilizer & composites (thread#3)

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AA 587 -- Vertical stabilizer & composites (thread#3)

Old 1st Dec 2001, 20:59
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Thanks InitRef. The NTSB recommendation (A-94-38) concerning inspection of composite structures seems very limited in extent:

"Require inspection using nondestructive ultrasound "A" scan inspection techniques of composite elevators on MD-11 airplanes that are known to have been operated outside the design buffet boundary."

I presume that the NTSB regards their other recommendations as sufficient to prevent the *first* operation of the a/c outside the design buffet boundary.

The NTSB report of this 1992 incident describes a very similar one (pitch and roll oscillations with elevator skin loss following turbulence) that happened to an Alitalia MD-11 on 26 Aug 93.
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Old 2nd Dec 2001, 17:54
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It's clutching at straws perhaps, but when you look for an initiator for that destructive flutter mode of AA587's fin and this AA rudder fish-tail (out of Lima PE on 28 Nov), you can only come up with three obvious common denominator type factors:

a. It can logically only start with the rudder (and the rudder's prime-mover is the hydraulic system) and thereafter potentially graduate to a rudder-induced flutter (catastrophically perhaps - as in the case of the AA587 fin separation).

b. It's occurring in the transition from lower towards higher speeds or vice versa (i.e. take-off into the climb or on approach as in the earlier AA Airbus A300-600 incident. That plane, on a flight from Colombia to Miami, Florida in 1999, had to abort its final approach after the pilots experienced what they called severe rudder deflection problems.)

c. It possibly needs an external initiator like wake turbulence (or is greatly excitated by the prime mover being an external force - such as turbulence-induced yaw).

The speed transition may be the clue as the rudder-limiter functions to limit rudder travel at the higher speeds (and conversely to de-inhibit it when the aircraft slows to approach type speeds). If there were to be set up a hydraulic hammering between the rudder actuator and the limiter valve that caused rudder fluctuations, it might plausibly explain how fin flutter could be thus "excitated".
But if so, how come it wouldn't be a more common occurrence? Well I guess the answer must be roughly the same reason why hydraulic hammer doesn't always happen in my house's plumbing. It depends which tap (faucet) you turn on (and how fast) and how long you run the water. It may also depend upon the water pressure. The airplane equivalent might be whether the rudder is being deflected by the autopilot, pilot's rudder pedals or the yaw damper - or perhaps the turbulence that you just flew through.

It may also be the case that something as simple as a (recent) FCS software patch could change the rate at which the yaw-damper or rudder responds, via the autopilot, to an externally applied yawing moment. That rate-change might be sufficient to set up that feedback "echo" between the rudder actuator and the limiter valve (or other hydraulic system component). Sometimes when you turn on a faucet in my house, the hammering is so bad you just have to turn it off and slowly back on - because that hammering has an ever-increasing amplitude and it sounds as if the walls are coming down. At other times it rattles away and then cancels itself out. In the airplane case, at 3000 psi a hydraulic hammer flinging the rudder left and right could be enough to set up that destructive aerodynamic fin-flutter. I'm not sure what (if any) trim, balance or servo tabs are on the rudder, or indeed how many actuators it has (but I presume three). The deflection of any secondary surfaces may be in that equation somewhere (also). AUW, CofG (and consequently the horizontal stabilizer's setting) could also be a factor.

It used to be the case that flutter was guarded against (damped) by aerodynamic (horns) and mass balancing ahead of a control surface's hinge-line. I believe that it's now done more scientifically by software control. It wouldn't be the first time that aviation has come up against unintended consequences of innocent or innovative modifications.

READ ALSO: http://www.aaib.dtlr.gov.uk/bulletin/feb01/n14065.htm Airbus A300B4- 605R, N14065 severe rudder yawing (27 Jun 2000)

"The loud bang reported by the crew could have been directly associated with the cause of the upset or could have been a secondary result of the movement of the aircraft". (I wonder if they would have carefully checked the engine pylon-to-wing attachments for cracks?)
The UKAAIB Conclusion: "The disturbance experienced by the aircraft could be attributed to a localised severe turbulence event."
(very facile IMHO - almost as good as a "miswired autopilot").
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Old 2nd Dec 2001, 22:39
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It may be more than straws because, so far, it looks like we have five A300 'uncommanded rudder' ..... incidents including this latest AA 587.

Note the lack of NTSB concern here in these - as evidenced by 'preliminary' reports still open or no apparent investigations at all. You would think these kind of incidents would be of real concern since they have no conclusions as to how this may have happened - repeatedly. One wonders if, like the four electrical failure modes known in the 737 'hard overs' that the answer may be simply "wiring" induced and perhaps merely to the rudder limiter system rendered to the 'ground mode' (or shorting intermittently). In the absence of an internal component failure, Hydraulics may just be the 'muscle' but Electricity can be the 'brains'.

Survey Of 4 Yaw Incidents BEFORE AA Flight 587.


Summaries: See referenced pages (below) here for more complete text and sources/URLs. [It's a downloadable file in rich text format].

With the exception the 5/11/99 incident, which is still 'preliminary', None of the other three (including the 10/3/99 incident said to have been investigated by the NTSB) are listed at the NTSB Monthly Accident and Incident database (http://www.ntsb.gov/NTSB/month.asp).

6/27/00. Airbus A300B4- 605R, Reg. N14065. As the aircraft was approaching FL220, at a reported airspeed of 325 KIAS, the aircraft experienced an abrupt disturbance which was perceived by the flight crew to be a disturbance in yaw with no attendant lateral motion evident in the resulting manoeuvre. They believed that the yawing motion had been caused by an uncommanded rudder input. The disturbance was accompanied by a loud bang which was noted by both the flight crew and some of the cabin attendants. They all reported the noise as being coincident with the disturbance. At the time of the event the aircraft was configured as follows: flaps and slats 'IN', landing gear 'UP', auto pilot 'OFF', pitch trim (systems 1 and 2) 'ON' and yaw damper (systems 1 and 2) 'ON'. The aircraft was clear of cloud and there were no other aircraft reported in the vicinity. Following the disturbance the aircraft appeared to behave normally. However, the commander decided to return to London (Heathrow) rather than commence a transatlantic flight following a suspected uncommanded flight control input. An uneventful, overweight landing on Runway 09L was completed at 1624 hrs. Ref. AAIB Bulletin No: 2/2001, ref EW/C2000/6/10. No cause attributed. See page 2.


10/3/99. A-300. American Airlines. During cruise flight, pilots experienced an uncommanded movement of the aircraft described as a "rudder jolt." Rudder system investigated by the NTSB. See page 5.


5/11/99. A-300. American Airlines. Flt 916 experienced multiple rudder deflections that caused the airplane to yaw excessively from side to side while on final approach to Miami. Ref. NTSB Monthly Report DCA99IA058 and NTSB AVIATION ACCIDENT/INCIDENT DATABASE REPORT. Report Number: DCA99IA058. See page 6.
This is still a PRELIMINARY Report in this NTSB database.

9/?/96. A-300. Near Luis Munoz Marin Int'L, PR. Aircraft started to shake and yaw with rudder pedal movement shortly after leveling at FL 310. The aircraft was slowed down and the flight characteristics returned to normal. An emergency was declared and the flight made an overweight landing at SJU. Ref. Aviation Safety Reporting System Report Number: 347914. See page 7.
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Old 3rd Dec 2001, 05:11
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I havn't read all the posts on this so forgive me if this is redundant, but I have heard that FedEx has grounded some of their A310's because they found a few that showed signs of delamination on the vertical stab. Any truth to this?
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Old 3rd Dec 2001, 05:16
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Dagger Dirk, if you add this incident (already posted elsewhere) then we may be looking at 6 total incidents of this type.

"LOS ANGELES (CNN) -- An American Airlines Airbus jetliner departing Lima, Peru, Wednesday evening experienced severe rudder problems during takeoff, forcing it to return to the airport, CNN learned Friday.

"The aircraft, an Airbus A300-600, is the same model aircraft as American Airlines
Flight 587.

"In Wednesday's incident in Peru, the pilots reported "fish tailing" soon after takeoff.

"An aviation source told CNN the aircraft experienced severe rudder fluctuations. A
preliminary NTSB report said the plane landed safely and its flight recorders have
been pulled for further investigation.


Here's the NTSB preliminary report...

NTSB Identification: DCA02WA011

Scheduled 14 CFRPart 121 operation of Air Carrier AMERICAN AIRLINES INC
Incident occurred Wednesday, November 28, 2001 at Lima PE
Aircraft:Airbus Industrie A300-600, registration: N7055A

American Airlines A300-600 flight reported "fish tailing" soon after takeoff from Lima, Peru, on November 28, 2001. The flight returned to land at Lima without injuries. The flight recorders were pulled pending possible readout.
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Old 3rd Dec 2001, 05:47
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According to the NY Post sunday, there were at least two witnesses to the initial loss of control of the A300, both of whom said they had a clear view and both were dissmissed, they say, by investigators. One was a police officer. Their story is that they clearly saw the initial explosion, and heard a sharp noise. The intitial explosion was alongside the fuselage, at the right side, and they said they saw the right engine come off after the airplane pitched down, followed by the vertical stab separation. But they say the stab did not seem, to them, to have initiated the chain of events. OK, they are not aviation trained, but maybe there is something in their stories.
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Old 3rd Dec 2001, 14:27
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I was once explained by a psy on an accident ivestigation that the memory can switch chain of events in case of psychological shock, such as witnessing an accident.
The "flames"and "explosions "or the noise of the explosion are generally what struck the memory brain and in re-collecting the events later, one would have the tendency to attribute this "shock "as the first event in the chain. This can be even collectively experienced by a group of witnesses, who saw an accident.
This is for this reason, that generally investigators do not consider eye witnesses reports as factual, and generally they are contradicted by the "hard "evidence such as FDR.
If, as you said, the NTSB diregarded the 2 eye witness accounts , that could mean that the chain of event is already well established by the FDR readings..
But all this is speculation of course...
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Old 3rd Dec 2001, 14:58
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This is the New York Post article, written by a columnist, and not carried as a news story. Again shows that what witnesses actually saw and what they think they saw often can be quite different. In AA587, the wreckage pattern and the flight data recorder contradict the two observations below.

"December 2, 2001 -- LITTLE wonder the National Transportation Safety Board has bleated for help from NASA to help them out in the tragic crash of American Airlines Flight 587. The NTSB has shown in the past that it is run by a bunch of bumbling bureaucrats who couldn't find a needle in a thimble.

"Here they were with 265 dead, and God knows how many mourners, giving us this claptrap that the tail fell off mysteriously.

""No tail fell off, not before the explosion. I swear to that," said retired firefighter Tom Lynch, who was doing his
exercise march along Rockaway Beach Boulevard on Nov. 12.

""I had my head up taking in that beautiful, clear day and was staring straight at the plane.

""It made a bank turn and suddenly there was an explosion, orange and black, on the righthand side of the fuselage. It was a small explosion, about half the size of a car.

""The plane kept on going straight for about two or three seconds as if nothing had happened, then ‘vwoof' - the second, big explosion on the right wing, orange and black.

""It was only then that the plane fell apart. It was after the explosion and I'm telling you, the tail was there until the
second explosion."

"Lynch, who lives near the crash site in Belle Harbor, claims he has 13 people who saw the plane on fire before the breakup. Until the explosion the tail was intact.

"He contacted the FBI, NTSB, Rep. Anthony Weiner, and Sens. Chuck Schumer and Hillary Clinton.

""I got no response from anyone," said Lynch, "Sabotage? That's for other people to decide. At first, we hear there were seagulls in the engine, the plane was caught in a jet stream and the tail fell off. No damn tail fell off until after the second explosion."

"Jim Conrad, who retired last month as a police lieutenant after 34 years, accidentally met Lynch in a dentist's office
one week after the crash.

""I saw exactly what Tom saw. I was near a stop light at the Marine Parkway Bridge. First, the small explosion. The plane kept on going, tail intact, then the big explosion and the plane nose-dived. The first thing I said was: ‘The bastards
did it again.'"

"For the NTSB to seriously speculate that the bloody tail fell off in the face of so much evidence that it didn't happen is
arrogant and treating us all like a bunch of morons.

"But NTSB spokesman Ted Lopatkiewicz said: "We don't have any evidence of an explosion [after searching] the wreckage or from the cockpit recorder. It doesn't mean it
didn't happen.""
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Old 3rd Dec 2001, 22:16
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Hate to be a "conspiracy nut", but as more and more detail produces more and more bafflement - seems there was a sharp hard explosion on one side of the plane leading to break-up.

Stinger, or some variation of MANPADS. I assume a bomb would have been noticed attached to the plane.

I am perplexed why this is not a very reasonable possibility which should be accepted until proven not to be the case. I mean, we are at war, arent we?

As far as I am aware the FBI is still involved.
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Old 3rd Dec 2001, 23:15
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Once the leading edge of the fin reached a certain point in its excursions, the resulting yaw may have been too much for the engine pylons; so, they could possibly come off first severing fuel, hydraulic, pneumatic and electric lines giving off both fuel and sparks including from all the breaking metal. Hydraulic fluid is petroleum based, i.e. flammable, and likely has a flash point considerably below jet fuel; its ignition could lead to ignition of the jet fuel.

As with the Sibir shoot-down by missile, a bomb or missile explosion would show abundant evidence of blast particles.
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Old 4th Dec 2001, 02:22
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Trader AL, When a main spar in a wing, tail or Pylon breaks, the resulting release of energy looks and sounds very much like a bomb.

Go find the films of the test of the 777 Wing SPar to destruction. When the SPar lets go it looks and sounds like someone exploded a bomb in the Boeing factory.

As a science experiment of your own, find a big dry stick and crack it, makes a lot of noise and releases a lot of energy into your hand. Now imagine a big I beam steel girder breaking (which is pretty much what the spar of a wing is, only bigger.)

Wino
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Old 4th Dec 2001, 03:58
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Aviation Week has an article and pictures (not the best quality) taken from an NSTB video of the vertical stabilizer. According to the Aviation Week article, different failure modes are seen in the lug attach points for the vertical stabilizer, including a skin delamination at the aft left attach point.
http://www.AviationNow.com/content/p...03/avi_air.htm
________________________________________
Trader, if you want to pursue conspiracy theories, the far better candidate is ascertaining who prepared and mailed the anthrax letters, --as it now seems spores of that quality and purified concentration were previously made only in U.S. Department of Defense biological-warfare laboratories. And as it seems no other country or group has ever achieved that level of capability.
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Old 4th Dec 2001, 21:25
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From the article at http://www.aviationnow.com/content/p...03/avi_air.htm

The A300 has a yaw damper that can move the rudder at a rate of up to 39 deg. per sec. Maximum throw is limited to 10 deg. at speeds below 165 kt., reducing to 2 deg. at maximum operating speed. The two-channel yaw damper actuator is separate from the autopilot yaw actuator, and yaw damper inputs are not felt at the pedals

The A300 has a rudder limiter that places variable stops on the actuator input, depending upon airspeed. Two computers electrically drive the stops. Full 30-deg. travel is allowed up to 165 kt., then it is cut back to 3.5 deg. at 395 kt.

...the rudder position measurement became unreliable 2.5 sec. before the FDR stopped. Lateral acceleration increased to 0.8g, an extreme value for forces in that direction. Based on radar data, the airspeed was about 250 kt. at that point.

From the NTSB Factual
Based on radar data, flight 587 took off approximately 105 seconds behind Japan Airlines flight 47, a Boeing 747. The FDR indicates that flight 587 encountered two wake vortices generated by JAL flight 47. The second wake encounter occurs about 8 seconds before the end of the FDR data. For the first few seconds after the second wake encounter, the aircraft responded to flight control inputs. Both wake encounters averaged about 0.1 G lateral (side to side) movement. During the last 8 seconds of FDR data, the plane experienced three stronger lateral movements, two to the right of 0.3 and 0.4 Gs, and then one to the left of 0.3 Gs. These lateral forces corresponded in time with rudder movements. The NTSB continues to investigate the cause of the rudder movements.
The Electronics are the brains, the Hydraulic actuators are the muscle, but the electrical inputs to those actuators are the messages that convey flight control system commands. Just wondering here if there may not be a wiring-related dimension to AA587 and the five other instances of A300 uncommanded yaw. Rudder pedal inputs, autopilot outputs, the yaw damper's signals and the rudder limiter's variable stops all depend upon wiring transmitting commands to the hydraulic actuators - and wiring can fail. It can fail intermittently. As per my earlier theory about hydraulic hammer, it is equally possible that the computer-selected rudder limiter's variable stop positions, which are electrically driven, could have been driven to distraction (or out of the equation) by a wiring fault.

Without a doubt the hydraulic system is capable of driving the rudder at a high rate to high deflections (circa 30 degrees), and if those variable stops were out of position, the forces on the fin as a result of a rapidly applied rudder "throw" would be destructive (fin flutter mode entered or not). Indeed the FAA had criticised American Airlines SOP's for unusual attitude recovery as being too reliant upon the rudder. They were concerned that this might cause fin overstress. So what would you need to look for by way of a fault? I would look for a rudder-related wiring bundle traversing a corner down there in the empennage, a metal edge upon which it could rub or chafe - and short or arc or interact inductively with another circuit. That bundle would possibly carry both the rudder limiter and autopilot-controlled FCS inputs to the rudder actuators (perhaps even the yaw-damper signals as well). I would look in all of the A300 aircraft (six to date) that have experienced this phenomenon.

But why would this have happened to AA587 during a wake encounter? Think of the rudder as being "normally neutrally dormant". That is to say that unless you have an engine failure or are recovering from an unusual attitude or carrying out a croswind landing, normally the rudder sits peaceably in trail and any yaw imbalance is compensated for by a combination of having symmetrically balanced engine power and via the autopilot-controlled rudder trim. The significance is this. If there were to be an electrical wiring "ticking" fault down around the tail it too could lie latently dormant until such time as the FCs (flight control system) had a need to make a significant input to the rudder actuator - during a rudder deflection or aircraft yaw induced by a wake encounter for instance. The FCS would call for a corrective rudder deflection but because of the wiring fault the rudder limiter's variable stops are absent - and so the FCS computer's very reasonable request (in percentage throw perhaps?) becomes a gross rudder deflection.

What happens next? This is where you need some systems knowledge and imagination (to be sure). Two things could happen next. Firstly the FCS computer would react to a massive yaw (that it hadn't ordered) by treating it just as it had treated the original gust response requirement - it would feed in a correction of an appropriate amplitude. Because this would be towards the NULL position of the rudder, an overthrow would be less/not likely. However the next lateral gust of the continuing wake encounter would bring about a repeat of the first massive yaw input. If you then get a little out-of-phase with the required inputs and the rudder exceeding max throw for that speed, well you might stall the vertical fin or it might enter a fin flutter mode. In the former case any stall would be momentary because the FCS corrective inputs would tend to immediately unstall the fin. But in the latter case, you could have a harmonic set up between the FCS computer calling for minor corrections and it becoming out-of-kilter with the rudder's over-travel. Because of the limiting stops being mispositioned the rudder travels further and because of that there is no longer any logical relationship between rudder response and the magnitude and periodicity of the FCS computer's commanded corrections. In simple terms it might then be zigging instead of zagging and amplifying the rudder/fin interaction (leading to the perplexing "rattle" heard on the CVR). An out-of-phase computer frantically driving an overthrowing rudder? I am trying to think of an analogy. Automotive understeer/oversteer? That unfortunately doesn't convey the correct imagery. Perhaps a temp datum system or prop control "hunting" around a mean? But in the case of a destructive rudder throw and an always lagging and out-of-phase FCS computer, the better simile might be the roller-coaster ride of a divergent phugoid - but around the vertical axis.

What about the incidents that weren't wake encounter initiated? Perhaps it's just one of those phantom ticking faults where the short (or ticking fault arc) makes and breaks as the fuselage flexes during the rudder-induced yaw and/or with the directional changes of the yaw. The thing to remember about wires in a wiring bundle interacting is that the manifestation can be in either or both associated systems. That is the phenomena unique to wiring-fault induced systems outages. It can be very perplexing, particularly if it's an intermittency. One manifestation can be a single rudder jolt, the other can be the compromise of the limiter's variable stops positioning. A third could be an uncommanded yaw-damper actuation.

If you examine the six incidents (see this rtf file) you will note that they are all "unresolved" - however they all have the smell of an intermittent electrical fault.
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Old 4th Dec 2001, 22:44
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Any system when it becomes unstable reacts in an unpredictable and totally random manner. Traffic flow is a good example. The reason that busy traffic on the motorway slows down and speeds up for no apparent reason is because the traffic flow rate exceeds the capabilities of the road network and the rate of traffic movement becomes unstable.
If for whatever reason, hydraulic or electrical, the system had become unstable then the effects would be totally unpredictable.
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Old 4th Dec 2001, 23:49
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I challenge the more learned readers of this forum to explain how a stinger or MANPADS could (not an automatic could not) have caused 587 with the results noted and documented to date.

Can it be done?

I think it behooves the people in the industry to try and prove is was a MANPADS first and then move on to other reasons if it can not be done.

Why? Simply because we are at war and those professionally involved in the industry are obligated to approach the crash in this fashion.

It seems most here have only cursory knowledge about MANPADS and retort with either a bias to purposefully ignore such avenues of approach (denial, fear, not chic in times prior to current war) by simply labeling it as "conspiracy theory" or alarmist etc etc etc ; or provide commonly held wisdom such as shrapnel or missile trails.

I am appealing for someone who knows MANPADS unequivocally to supply some information, not parrot belief systems. I am asking, not challenging. Begging really. And I would actually prefer the outcome of such scrutiny to arrive at the conclusion that most on this forum wish to immediately leap towards.

As I have mentioned before, one such "expert" I am in touch with on first hand, who use to deploy MANPADS for elite military squads in a past life (Stinger used by SOPs) says all he has seen of 587 is consistent with what he knows a Stinger does. This man was a soldier on the ground, not a pilot. He looked up, not down.

Are there other "experts" who can also provide information to such a view? This "expert" I know claims Stingers do not provide shrapnel debris or fire damge, but produces a massive air blast which rips appendages from the main body of an AC. From this person's point of view, he would not at all find a "pristine" tail assembly to disprove a Stinger hit, but would expect that sort of damage.

That is the full limit of my info from an expert in MANPADS.

I also know a bit about composites, enough to risk making a fool out of myself in front of such readership as this forum, having worked with them on large sailing crafts in spars and hulls. I do know that they are 100% reliable and better than metal over the life of the craft provided they do not "blow-up" almost immediately with any sort of trial at sea. They do not blow up after being used for 10 years or so. I also know that at sea, a tried and true composite hull/spar is something I would find much more comfort in than metal. Personally, I would prefer a woven 6 or 7 layered fiberglass hull to an aluminum hull in the midst of a storm. I also would not have any doubts over my carbon fiber mast provided it had already gone through such a storm. If the boat had not had such sea-test,I would prefer metal and wood. Obviously this is an analogy considering 587 was a well "sea-tested" craft.

What I find alarming is that previously held conceptions developed from, mainly, TWA 800 investigations are being used towards 587 without thought to the current context. I personally found that the idea of a missile was far fetched for TWA 800.

But.

May I remind this readership that we are at war with an enemy who already has achieved the fantastic. Ask yourself, if I described the potential for the WTC last year, would you have laughed and scolded me out of this forum? Would it be considered mere "conspiracy theory" and suggest I was the worst kind of nut, a lay person nut? Would Capt Pprune shut me down immediately?

I think it is sober and pragmatic to ask those who know, not those who think they know, for solid evidence that a MANPADS was a possibility in regards to 587. If such evidence cannot be provided, or if affirmation of the damage is ocnsistent with a Stinger can not be provided, then we shoudl move on to non-war scenarios. To date I have had contact only with one such "expert", someone who has actually fired the things, and I am disturbed with his thoughts.

In North America, if one hears hoof beats behind you, chances are it is a horse, not a zebra. We are at war.

If such a possibility of a MANPADS causing 587 can be easily eliminated, not from surmise but rather as it can not be shown to fit the cause by an expert, that a reasonable scenario cannot be made for this agent causing 587, then we move on to NASA and mystery. There is no mysterious conspiracy out there, there is a conspiracy! What more than WTC and Ridge declaring an "alert" is required to show the seriousness of the situation?
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Old 5th Dec 2001, 00:31
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FFFlyer: I disagree with your statement that electronic or mechanical 'systems' typically become totally unpredictable and random when they enter "unstable" territory. It is very hard to get real things to behave randomly. Closer to the mark is to say that they will behave in an 'uncharacterized' manner which may be counterintuitive at first brush. An inherent problem with the complex control processes that result when pilots and aircraft combine with digital and analog electronics, mechanical actuators, and sensors is that they can have unwelcome behaviors in boundary conditions. The #1 principle of designing and making control systems is: if a function, mode, condition, etc. hasn't been specifically simulated or tested, one cannot know with any confidence what will really happen in that case.

DAGGERDIRK: IMHO, your suspicion re a non-obvious fault mechanism in the controls warrants exploration. You assume that the rudder travel stops are mechanical or quasi-mechanical, but is that really the case? If they are being changed in complex ways in real-time, it would make sone sense to put those interlocks into one or another level of software (or electronic hard-wired) loop. At a minimum, some secondary process controls the stops, n'est ce pas?

A complex set of sensors, manual controls, actuators, electronics and computer programs interact with aerodynamics and crew commands to determine the actual rudder movement in real time. Surely the control process has n-many operational 'modes', each with its own behavior plan, priority, and inherent speeds, delays, and damping factors. Somewhere in there may be an unexamined sensitivity to, say, climb attitude, sudden lateral acceleration from wake, noisy or intermitent sensor response, pilot/autopilot rudder input, and fuselage resonances - the sensor responses to the second, etc, reflections of the sharp wake bumps as they bounce around the airframe / engine mechanical matrix. In short, there could be a 'bug' in the time-dimension responses of the control system.

Whatever the cause of this tragic accident, I strongly believe that future aircraft designs should include secondary FDR's -plus aditional sensors- that are easily and routinely offloaded after each flight - with the full envelope of flight data for each individual bird captured and stored for the entire service life of the aircraft fleet - and beyond. SOP copies to the factory, every bit of data automatically analyzed there and used to confirm and refine design engineering and maintenance assumptions. Faults usually manifest in small ways before the big one. Better to have the aircraft tell us what they're up to while still in one piece.

Ditto on composites. I have seen published practical methods to fabricate sensors into aircraft composite structures and elements so they can me monitored in real-time through their entire operating life.

Maybe new aircraft should use more of the technology that is readily available to do more/better self-diagnosis. Diagnostic systems are unobtrusive and not inherently very expensive, next to the cost of insurance settlements, nor do they significantly compromise aircraft design, weight or safety. They do improve the ability to find design and wear problems, to track operating results, and to find the 'glitches' before destiny does.

[ 05 December 2001: Message edited by: systemsguy ]
arcniz is offline  
Old 5th Dec 2001, 06:10
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Trader Al, you persist in seeking to have someone, anyone, prove a negative to you. For whatever reason, you seem to have convinced yourself that this plane crashed as a result of a terrorist act because the United States is at "war"; and, ipso facto, all plane crashes that occur during wartime must first be shown as not having been the result of eneny action before other causes can be investigated.

In applying your wartime postulate to AA587, you choose to ignore every bit of evidence to the contrary, and drag in a so-called 'expert' who was not there, who has not seen the wreckage, who has not reviewed the data recorders, yet who posits that the crash is apparently similar to what he has observed after supposedly firing a MANPADS at an airplane.

Your last post declared: "This "expert" I know claims Stingers do not provide shrapnel debris or fire damge, but produces a massive air blast which rips appendages from the main body of an AC. From this person's point of view, he would not at all find a "pristine" tail assembly to disprove a Stinger hit, but would expect that sort of damage."

The Stinger has a 2.2 lb. penetrating high explosive warhead. (Stingers use a passive infrared system to home in on targets.) A penetrating warhead uses impact and explosive self-destruction to destroy the target, and it is not a proximity airburst weapon.

Thus, one should expect to find evidence of impact and explosion in the wreckage of AA587, including on the vertical stabilizer and rudder as these parts departed the aircraft first. Presumably, to fit your hypothesis, this is where the missile would have hit. (You may wish to review the NTSB preliminary examination of the FDR and the physical examination of both engines and note that both engines were operating normally up to the point they separated, which would seem to indicate that neither engine was hit by a hypothetical missile.

BTW, I'm sure NASA has yet to prove to a few souls out there that the manned lunar landing was not staged on a Hollywood backlot. After all, Hollywood subsequently went on to make a movie, Capricorn One, on just such a premise.
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Old 5th Dec 2001, 09:22
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Heres a question for all of the conspiracy theorists and the "eyewitnesses" - If there was an explosion and an engine fell off and then the tail came off how did the tail wind up in the water and both engines come off further along the flight path over land? Unless I am missing something here it seems that the eyewitness reports do not match physical evidence.

As to the question of stingers or other ground launched missiles - unlike Afghanistan it would be extremely difficult to obtain or import one into the US. In addition all of these ground launched missiles usually create a huge exhaust plume when the back blast of the missile motors igniting stir up all the cr@p in the immediate vicinity of the launcher - this would be hard to hide as well.
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Old 5th Dec 2001, 18:18
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AD/AB3/107 Rudder Trim Control Switch 9/97


Applicability: All models A300-600.

Requirement: Replace control switches P/N 097-023-00 with new switches P/N 097-023-01 in accordance with Airbus Industrie Service Bulletin A300-27-6037.
Note 1. AD/AB3/90 is cancelled.
Note 2. DGAC AD 97-111-219(B) refers.
Compliance: Unless previously accomplished prior to 14 January 1998.
This airworthiness directive becomes effective on 14 August 1997.
Background: The actions required by this AD are to prevent any interference between the 408VU panel and the rudder trim control knob, which could prevent the self recentering of the switch to the neutral position when released, thus causing a rudder movement up to the maximum deflection, and which could lead to critical flight situations. AD/AB3/90 required an ongoing compliance whenever the switch was replaced. This AD supersedes AD/AB3/90 and constitutes terminating action for that AD
http://www.casa.gov.au/avreg/aircraf...B3/AB3-107.HTM
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Old 5th Dec 2001, 18:52
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This is why I am looking for someone who knows, as the following quote is a good illustration of the current dismissive cant:

"The Stinger has a 2.2 lb. penetrating high explosive warhead. (Stingers use a passive infrared system to home in on targets.) A penetrating warhead uses impact and explosive self-destruction to destroy the target, and it is not a proximity airburst weapon."

That I know is not true, they work on a proximity airburst. That I do know. Their guidance system is infrared but also has sophisticated software which prevents the missile, as it moves so much faster than the plane, especially at only a few thousand feet in take -off, to bypass the target so they allow for the proximity burst. he software also serves so the missile does not strike at the engine or heat source but in proximity.

This is why I am concerned as to date all we hear are cant, brief condescending dismissive gestures and disinformation. I am not out to promote a thesis but to shed the thesis. It seems by even mentioning the topic one is branded a "conspiracy nut". But the thesis cannot be shed with simple pitying glances and disdain for the unwashed ones who pose the question. Answers to date in regards to MANPADS are cant, not analysis. The above quote is from someone who does not work with Stingers or know their ordance, but someone like me who has simply lifted data to suite their objective from the web.

I have a fear this will play opposite from TWA 800, where the FBI panicked and instantly jumped to the view that there was a bomb, then as the facts bcame apparent they had already done the damage and to this date have a pack of conspiracy folks chewing over TWA 800. This time there does exist a deadly and unprecedented conspiracy. But rather than deal with/in that context, the NSTB immediately stepped in with what seemed to be a pre-arranged strategy and precluded the FBI. But the FBI now keeps in contact just as the NSTB did in the first phase of TWA 800. Beyond firm dismissive sentence with no analysis, except that terrorists were not heard in the cockpit and no sign of any on board bomb, I have heard nothing definitive in regards to MANPADS. I really really wish I could hear something.
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