AF 447 Search to resume
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Thanks for the clarification, mm - language problems as always - spit!
PJ - the only comment I have is my surprise when I was firmly informed by a couple of BA guys that in a lot of cases 'breaks' are rostered and mostly not interfered with.
Probably not your way or mine, but 'it' appears to be out there.
PJ - the only comment I have is my surprise when I was firmly informed by a couple of BA guys that in a lot of cases 'breaks' are rostered and mostly not interfered with.
Probably not your way or mine, but 'it' appears to be out there.
BOAC;
Well, there may be some justification for this approach, based in the research on fatigue, sleep patterns and brain activity and the fact that none of us are the best judge of when we are fatigued or too groggy (after a deep-REM sleep during the break - we know that is to be avoided) to be in the seat right away. So I can understand if an organization has rostered breaks based upon these understandings if that's why and how it's done.
That said, just like any scheduling activity, by definition such does not take into account variations in circumstances and I think, within reason, crews should have the freedom to alter rostering schedules, followed by an air safety report so that reasons can be trended and modifications made to such rostering requirements.
PJ - the only comment I have is my surprise when I was firmly informed by a couple of BA guys that in a lot of cases 'breaks' are rostered and mostly not interfered with.
That said, just like any scheduling activity, by definition such does not take into account variations in circumstances and I think, within reason, crews should have the freedom to alter rostering schedules, followed by an air safety report so that reasons can be trended and modifications made to such rostering requirements.
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Diversification
Yes, the Arm failed while in tension, ostensibly "picking up" Stress produced in the Rudder's "Down Axis". Yes, again, for the Rudder to have endured its damage from the tail cone, the vector would have been opposite, in the "up" vector, as the Rudder was pinned to the upper Fuselage and the VS kept going. This holds true with the Rudder in a variety of deflection angles. So the "prying off" theory needs another look.
It may have been weakened by corrosion, these Hinges are open to the Air. Also, the Bolt seems to have remained in its position, meaning that there was little tension damage (if any) to the remaining Arm. Also notice that the Pivots of the Hinge, the two plates bracketing the joint from the Aft Spar of the VS, seem unscathed. There is no deflection or cracking of these plates nor the pin carriage on the Rudder. The Hinges must remain oriented in a straight line, if there is deviation from straight, the Hinge can "Bind" and cause problems with the actuator.
Something does not square in the description of Rudder Hinge failure. If the Vertical Arm breaks before the Hinge does, it is apparently not intended to prevent catastrophic failure and Rudder separation, and if the Rudder Hinge is not damaged, why then is this Arm present? Alas, the Arm failure occurred at the place of minimum material, so by interpretation, the length of the Arm that is composed of additional Metal is overengineered. One wonders why the Bolt/Arm mate is not built with additional structure, eg, an "Eye" (a circular pan with its hole in center of sufficient diameter to preclude a failure here; the Hinge end of the Arm is tapered, and I assume the "Barrel face" is radiused to conform to the circumference of it's round bed).
The simple way to see this is to say that in spite of the horrific load the VS and Rudder endured, it was the VS that failed, and separated from the a/c, not the Rudder. Also if there was sufficient energy to shear the VS, that same energy failed to separate the two surfaces. As you say, the bit of Arm that snapped off looks like a corrosion crack/fail.
The engineering consideration of the VS join is lateral energy, obviously for the ability to handle very serious loads imparted by the Rudder. The collateral consideration is simply to remain with the Airframe. BEA'S theory of vertical failure happens to pinpoint a stress for which the assembly is built exceptionally strong, but not as a result of consideration of failure in this direction. It is a bonus that derives from the VS' layout atop the Fuselage. Given that there was upset, loss of control, and impact in the Water, I simply maintain that it is strange, no, highly strange that the vertical Stabiliser was torn out virtually "over itself" and in a mode that is resisted in the VS structure here, with the presenting energy defying great odds. Possible.
bear
Yes, the Arm failed while in tension, ostensibly "picking up" Stress produced in the Rudder's "Down Axis". Yes, again, for the Rudder to have endured its damage from the tail cone, the vector would have been opposite, in the "up" vector, as the Rudder was pinned to the upper Fuselage and the VS kept going. This holds true with the Rudder in a variety of deflection angles. So the "prying off" theory needs another look.
It may have been weakened by corrosion, these Hinges are open to the Air. Also, the Bolt seems to have remained in its position, meaning that there was little tension damage (if any) to the remaining Arm. Also notice that the Pivots of the Hinge, the two plates bracketing the joint from the Aft Spar of the VS, seem unscathed. There is no deflection or cracking of these plates nor the pin carriage on the Rudder. The Hinges must remain oriented in a straight line, if there is deviation from straight, the Hinge can "Bind" and cause problems with the actuator.
Something does not square in the description of Rudder Hinge failure. If the Vertical Arm breaks before the Hinge does, it is apparently not intended to prevent catastrophic failure and Rudder separation, and if the Rudder Hinge is not damaged, why then is this Arm present? Alas, the Arm failure occurred at the place of minimum material, so by interpretation, the length of the Arm that is composed of additional Metal is overengineered. One wonders why the Bolt/Arm mate is not built with additional structure, eg, an "Eye" (a circular pan with its hole in center of sufficient diameter to preclude a failure here; the Hinge end of the Arm is tapered, and I assume the "Barrel face" is radiused to conform to the circumference of it's round bed).
The simple way to see this is to say that in spite of the horrific load the VS and Rudder endured, it was the VS that failed, and separated from the a/c, not the Rudder. Also if there was sufficient energy to shear the VS, that same energy failed to separate the two surfaces. As you say, the bit of Arm that snapped off looks like a corrosion crack/fail.
The engineering consideration of the VS join is lateral energy, obviously for the ability to handle very serious loads imparted by the Rudder. The collateral consideration is simply to remain with the Airframe. BEA'S theory of vertical failure happens to pinpoint a stress for which the assembly is built exceptionally strong, but not as a result of consideration of failure in this direction. It is a bonus that derives from the VS' layout atop the Fuselage. Given that there was upset, loss of control, and impact in the Water, I simply maintain that it is strange, no, highly strange that the vertical Stabiliser was torn out virtually "over itself" and in a mode that is resisted in the VS structure here, with the presenting energy defying great odds. Possible.
bear
Last edited by bearfoil; 9th Mar 2010 at 01:21.
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4Greens
The Nuclear Attack Submarine(SNA) "L'Emeraude" was on location 9 days after the crash, and remained for another 30 days. From where-ever the sub came from takes time, and primary functions such as storing and crew changes etc.. need to be made before such a commitment can be made.
That's accepting that there may well have been other "lurkers" in the area earlier - such is the intrigue of international espionage.
mm43
The Nuclear Attack Submarine(SNA) "L'Emeraude" was on location 9 days after the crash, and remained for another 30 days. From where-ever the sub came from takes time, and primary functions such as storing and crew changes etc.. need to be made before such a commitment can be made.
That's accepting that there may well have been other "lurkers" in the area earlier - such is the intrigue of international espionage.
mm43
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AF 447
Cause? Read the report done by KIRILL MINOVALOV flying his Citation X into Moscow on a stormy night. He got away with it. Google it!! He has just given evidence at the inquiry in Paris and it sounds very very interesting.
Last edited by CaptainSAC; 9th Mar 2010 at 15:42. Reason: Wrong spelling of name. Thanks
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Arm 36 g again
After a lot of thinking about how the badly corroded end of arm 36 g could have played a role in the accident, I now think that it is irrelevant. It points more to a potential danger in future flights, had the aircraft escaped this time. A total failure of both sides of this arm could have a rather bad effect on rudder movability. Probably Airbus will have to look into the inspections required in order to find if other aircrafts have the same corrosion problem.
Last edited by Diversification; 9th Mar 2010 at 17:24. Reason: Changes 62 g to 36 g
A VS separation would result in a high forward speed impact with the sea rather than a low forward speed, high vertical velocity impact. The evidence just isn't there for any high forward speed impact. Fragmentation of interior cabin parts was not high in this accident. Large, relatively fragile structures survived, intact.
Neither do I think that there is much to learn that we don't know already from the Japan Air B747 which lost the VS through loss of the aft pressure bulkhead and AA 587, in terms of pilot handling
Neither do I think that there is much to learn that we don't know already from the Japan Air B747 which lost the VS through loss of the aft pressure bulkhead and AA 587, in terms of pilot handling
Dear PJ,
In relation to your first comment, that a loss of the VS would necesarily result in a high forward speed impact, I doubt that this is sustainable as an outcome. On loss of the VS/Rudder assembly, the aircraft will be at best left with marginal lateral stability, and at worst will be divergent in yaw, which we have seen in the failure of AA587.
In relation to the second comment re pilot handling, do you not consider that a design certification criteria and subsequent design that can be overloaded by sequential torsion-bending loads within the limits of the rudder force (ratio) limiting system is not a factor rather than merely pilot handling? Note as well, that the functional design approach taken by AI on the rudder limiting effectively increases the sensitivity of the rudder in respect to the operators input. ( the system limits throw of control, and thereby rudder deflection, not reducing rudder deflection but maintaining the control throw). Further, the AA587 loss highlighted the massive misunderstanding of operators generally as to the application of Va.
In the event of a compound ADC failure, all bets are off as to control gain and FBW stability systems, and the potential in moderate severe turbulent conditions to result in a control system initiated structural failure remains possible. This is not limited to pilot only control inputs, as the FBW system would until reverting to direct law be acting in 2 channels to retain attitude. Whether this did in fact occur to 447 remains an open question, but is probably inconsistent with the BEA's observation of a failure of the VS/rudder on water impact. I personally find that opinion, and the available data inconsistent, suspect that the loss of data airborne and the preceding system degradations indicative of structural failure airborne, with VS separation a potential consequential failure following the ADC and turbulence encounter.
Rather than having a high speed impact following an inflight VS separation, I would be expecting a relatively low speed impact, potentially with moderate vertical rate. Note that even with JAL103, which retained some lateral stability, the KCAS varied enormously as a consequence of the phugoid, from near stall to high speed. On AA587, the VS failure resulted in divergence in yaw (with beta dot much higher than encountered during the control input phase pre VS separation), and rapidly the separation of both engines under excessive lateral load of the pylon attachments. The aircraft at this point had no thrust, hydraulics, and was pretty much limited to uncontrolled directionally unstable descent as a falling object with path modified by the remaining aerodynamic appendages operating at varied relative airflows.
Just a thought...
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Having thought a bit about how an "intact" hull would react on impacting with the water in the following configuration:-
Pitch Attitude +5°
Bank 0°
Rate of Descent 9,120 ft/min (90KTS)
Ground Speed 50KTS
Heading +10° relative to direction of flight probably in a flat spin clockwise
Initial contact of the empennage would have caused a rapid reduction in pitch, the engines (if still attached) would bite into the water, and as the main wing span impacted, the g forces between the engines and their pylon mounts would have resulted in them shearing off and heading straight down.
Deformation of the empennage and the fuselage aft of the wing will have resulted in a vertical fracture at this point, and similarly to the fuselage forward of the wing. These fractures would have opened fairly cleanly as the result of impact g forces rapidly reducing to zero, then followed by the reciprocal moment due to initial buoyancy and the water rebounding and overshooting its original level before dampening down over a few more cycles. The forward, middle and aft sections of the fuselage all acted differently, with the largest g forces being sustained by the wing section, due to its much bigger volumetric area.
If you need a little help in imagining this, then get a small round plastic pill bottle, add about third of it's volume in soft brown sugar (gets rid of any free surface effects if water is used) to it and replace the cap. Lay it on its side, tap it to ensure the sugar settles along its length, then drop into a bucket / bath etc.. of water on its side and watch what happens!
This accident bears no relationship to the Ethiopian 767 ditching in 1996, where forward moments were reduced by the left wing slicing into the water first, catching a coral reef, and the aircraft rolling and breaking up in the swell.
The point I am making in respect of AF447, is that hitting terra firma in the configuration described above, would have resulted in an impact crater, major disintegration of wings and fuselage followed by fire. This didn't happen, and the reciprocal moments generated by this sort of impact with terra oceania need to be taken into account when discussing the manner in which the vertical stabilizer could have left the empennage anchor points. Not to put too finer point on it, the seat belts didn't cause the damage they are reported to have done due to the impact acceleration to zero, but the substantial reciprocal moment caused by the sea and initial buoyancy, will have. Just think of being belted in on the wrong side of a slingshot that had been tensioned down, then released.
mm43
Pitch Attitude +5°
Bank 0°
Rate of Descent 9,120 ft/min (90KTS)
Ground Speed 50KTS
Heading +10° relative to direction of flight probably in a flat spin clockwise
Initial contact of the empennage would have caused a rapid reduction in pitch, the engines (if still attached) would bite into the water, and as the main wing span impacted, the g forces between the engines and their pylon mounts would have resulted in them shearing off and heading straight down.
Deformation of the empennage and the fuselage aft of the wing will have resulted in a vertical fracture at this point, and similarly to the fuselage forward of the wing. These fractures would have opened fairly cleanly as the result of impact g forces rapidly reducing to zero, then followed by the reciprocal moment due to initial buoyancy and the water rebounding and overshooting its original level before dampening down over a few more cycles. The forward, middle and aft sections of the fuselage all acted differently, with the largest g forces being sustained by the wing section, due to its much bigger volumetric area.
If you need a little help in imagining this, then get a small round plastic pill bottle, add about third of it's volume in soft brown sugar (gets rid of any free surface effects if water is used) to it and replace the cap. Lay it on its side, tap it to ensure the sugar settles along its length, then drop into a bucket / bath etc.. of water on its side and watch what happens!
This accident bears no relationship to the Ethiopian 767 ditching in 1996, where forward moments were reduced by the left wing slicing into the water first, catching a coral reef, and the aircraft rolling and breaking up in the swell.
The point I am making in respect of AF447, is that hitting terra firma in the configuration described above, would have resulted in an impact crater, major disintegration of wings and fuselage followed by fire. This didn't happen, and the reciprocal moments generated by this sort of impact with terra oceania need to be taken into account when discussing the manner in which the vertical stabilizer could have left the empennage anchor points. Not to put too finer point on it, the seat belts didn't cause the damage they are reported to have done due to the impact acceleration to zero, but the substantial reciprocal moment caused by the sea and initial buoyancy, will have. Just think of being belted in on the wrong side of a slingshot that had been tensioned down, then released.
mm43
Last edited by mm43; 10th Mar 2010 at 02:30. Reason: got rid of a spare "a"
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wizele . . . if you're a pilot, you should know that journos often misinterpret aviation jargons; and Der Spiegel is hardly an aviation journal.
The "Bordeaux" en route alternate airport is just for planning purposes. It doesn't mean that if the flight couldn't make it to CDG that it must land at BOD.
If you study your big atlas you will see that there are many airports in NW Africa that could be used for diversion if there were a significant over-burn and adequate fuel to BOD became an issue.
In any case, pilots do not forego weather deviations to conserve fuel.
The "Bordeaux" en route alternate airport is just for planning purposes. It doesn't mean that if the flight couldn't make it to CDG that it must land at BOD.
If you study your big atlas you will see that there are many airports in NW Africa that could be used for diversion if there were a significant over-burn and adequate fuel to BOD became an issue.
In any case, pilots do not forego weather deviations to conserve fuel.
Deformation
MM43, presume the empennage slowed rapidly on contact, rest of structure carries on progressively being decelerated, rear fuselage shears early on owing to the differential accelerations with VS detaching some time in the sequence owing to differential accelerations between it and the (residual) fuselage. Rear section then sinks taking its witness marks and downward twisting with it. Are there any signs of compression at the base of the VS ?
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mm43
With respect, your last entry is perhaps rather too harsh on the 330 airframe. In recent years, given the sparse quantity of accidents to assess, one can come up with parallel impacts in which the Tail/Vertical stayed together. This presumes, of course that the speeds are reasonably accurate, as you quote: 100knots vertical, 50 knots horizontal. I believe these speeds are quite low, that the impact involved a great deal more energy than is commonly perceived.
Turkish. In a Stall, the 737 struck the turf Tail first, and the fuselage pancaked and separated into the sections you describe.
Colgan. Here, there is a strong parallel to 447's "impact". Stalled, pancaked, destroyed in subsequent fire.
DFW. Caught in shear, the 1011 hit tail first, broke up and burned
UAL 187. At 180 knots, the DC-10 hit in a "landing" aspect, broke up and burned.
Consider that all these a/c impacted in similar fashion. Tail first, with a velocity of >50 knots, and with varying vertical speed.
In all of the above, the Tail survived attached to the fuselage.
447's impact (as presumed) is not in itself radically different from others.
With a horizontal component, there would be some "bounce, skip" of the Tail, immediately reducing the full force of the vertical, iow, it hit at an angle.
Look at the mounting bed of the VS per 587. Singed but intact. This 300 hit nose first at high vertical acceleration, the VS/Rudder, and Fuselage underneath the VS were intact, though not attached.
447: I wouldn't discount the energy involved, it was almost certainly higher than proposed by BEA. "High vertical acceleration". As a conclusion, it is a poor one, it is a guess without fact, a statement w/o supporting evidence, unless one adds two guesses up to equal a "Finding". I will include Mr.Optimistic's point re: Compression/VS, it is a sound one.
With respect, your last entry is perhaps rather too harsh on the 330 airframe. In recent years, given the sparse quantity of accidents to assess, one can come up with parallel impacts in which the Tail/Vertical stayed together. This presumes, of course that the speeds are reasonably accurate, as you quote: 100knots vertical, 50 knots horizontal. I believe these speeds are quite low, that the impact involved a great deal more energy than is commonly perceived.
Turkish. In a Stall, the 737 struck the turf Tail first, and the fuselage pancaked and separated into the sections you describe.
Colgan. Here, there is a strong parallel to 447's "impact". Stalled, pancaked, destroyed in subsequent fire.
DFW. Caught in shear, the 1011 hit tail first, broke up and burned
UAL 187. At 180 knots, the DC-10 hit in a "landing" aspect, broke up and burned.
Consider that all these a/c impacted in similar fashion. Tail first, with a velocity of >50 knots, and with varying vertical speed.
In all of the above, the Tail survived attached to the fuselage.
447's impact (as presumed) is not in itself radically different from others.
With a horizontal component, there would be some "bounce, skip" of the Tail, immediately reducing the full force of the vertical, iow, it hit at an angle.
Look at the mounting bed of the VS per 587. Singed but intact. This 300 hit nose first at high vertical acceleration, the VS/Rudder, and Fuselage underneath the VS were intact, though not attached.
447: I wouldn't discount the energy involved, it was almost certainly higher than proposed by BEA. "High vertical acceleration". As a conclusion, it is a poor one, it is a guess without fact, a statement w/o supporting evidence, unless one adds two guesses up to equal a "Finding". I will include Mr.Optimistic's point re: Compression/VS, it is a sound one.
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So Bearfoil
Isn't everyone on this thread dancing around the very frightening notion that the VS separated in flight due to unexpected aerodynamic loads or pilot-induced loads? Such would certainly produce a flat spin. How could this happen?
I can accept one incident (587) in which pilot inputs break the airplane (though I don't buy this explanation at barely above maneuvering speed), but two, with the same sort of failure?
I am a former round-motor driver who finds himself SLF on the 330 at least once a month on non-aviation related business, and am regrettably not an engineer. I like the Airbus' comforts and hold no grudge for EADS nor any prejudice in favour of Boeing, whose 737 rudder hard-over issue was neatly covered up. And I confess I couldn't navigate myself around a glass cockpit for 2 minutes. So, ignoramus, yes... but!
When the second Lockheed Electra L-188 shed a wing in flight the manufacturer pulled out all stops, including enlisting NASA, to discover the cause (an unfortunate harmonic in whirl mode that broke the main spar). They fixed, at their own cost, every L-188 in revenue service. The speed with which Lockheed responded was commendable.
Now we have at least two Airbii that have died in-flight with vertical stabs found a bit of a distance from the rest of the airframe. Odd coincidence here: the errant L-188 wing was found a bit of a distance from the rest of the airplane.
Lockheed swallowed their pride and fixed their mess in quite a public way. Will EADS do the same?
I can accept one incident (587) in which pilot inputs break the airplane (though I don't buy this explanation at barely above maneuvering speed), but two, with the same sort of failure?
I am a former round-motor driver who finds himself SLF on the 330 at least once a month on non-aviation related business, and am regrettably not an engineer. I like the Airbus' comforts and hold no grudge for EADS nor any prejudice in favour of Boeing, whose 737 rudder hard-over issue was neatly covered up. And I confess I couldn't navigate myself around a glass cockpit for 2 minutes. So, ignoramus, yes... but!
When the second Lockheed Electra L-188 shed a wing in flight the manufacturer pulled out all stops, including enlisting NASA, to discover the cause (an unfortunate harmonic in whirl mode that broke the main spar). They fixed, at their own cost, every L-188 in revenue service. The speed with which Lockheed responded was commendable.
Now we have at least two Airbii that have died in-flight with vertical stabs found a bit of a distance from the rest of the airframe. Odd coincidence here: the errant L-188 wing was found a bit of a distance from the rest of the airplane.
Lockheed swallowed their pride and fixed their mess in quite a public way. Will EADS do the same?
Isn't everyone on this thread dancing around the very frightening notion that the VS separated in flight due to unexpected aerodynamic loads or pilot-induced loads?
There are a whole bunch of that don't dance but stand square shoulder against drawing conclusions prematurely without data.
Lot's of folks try "what'ifs" but lacking the ability to convince the majority these also fade into the darkness as we all await another tidbit of real data rather than hypothesis alone.
If you understand investigative techniques please feel free to contribute. If you don't then don't be swayed by someone elses arguments on the internet.
fdr;
Thanks for your input and observation. Your posts on PPRuNe may not be many but they are worth reading. I may have some B777 questions for you.
With loss of the VS, (I am imagining your scenario at high altitude, not lower down) I wasn't thinking a longitudinally stable trajectory as a scenario in a high speed descent - it isn't possible without lateral stabilization. I would expect strong roll due to yawing, loss of the engines due yaw/roll and a high speed descent of what remained of the airplane. For me, the parts that remained of the cabin structure, (from cockpit to rear galley) either indicated an intact-fuselage as described in the BEA report or a mid-air break up of the fuselage. Perhaps your scenario, (low speed descending spin after loss of the VS at high altitude, I think?) may have obtained. I don't think so, but that doesn't matter; as with every scenario, it is at this point where we must wait.
As far as AA587 goes, I know there is substantial controversy regarding the conclusions and reasons for the loss of the vertical stabilzer and that APA has provided significant input. My thinking and therefore my opinion on the design of the AI VS is unimportant as I am not an engineer and cannot validate design. I believe however that this fashion of attaching the VS to the fuselage is the way it is done throughout the industry.
Regarding use of the rudder, I can offer the following:
I have to say that I knew very early on that use of the rudder on a jet transport was discouraged except to keep the aircraft straight during an engine failure and to align the aircraft with the runway in de-crabbing during a cross-wind landing. Otherwise one kept one's feet on the floor.
In the very early 70's, "Jet Upset" did not exist as a concept or a cause of an accident and so was never discussed. In any later (post 2000 or so), jet upset literature we had access to, (we were not, and to my knowledge, still are not, taught recovery from jet upset in the simulator), use of the rudder was specifically warned against.
As a result of all this I would never have expected the use of the rudder in the manner indicated in the AA587 data, not because I thought it might break the VS but simply because one just never did that with the rudder in a jet transport...I never thought there were ever any circumstances in which it was required and while I've certainly experienced wake turbulence at low and cruise alititude, use of the rudder to control the airplane just wasn't a consideration, not from AA587 on but right from the beginning of the career. I think that I wasn't unusual in this understanding.
That said, I wasn't on the flight deck of AA587 so don't know what they faced.
I read with interest both bearfoil's and mm34's input, especially the notion of a sacrificial rudder vs the loss of the VS. The merits of such notions may already be under examination, we don't know.
As has been pointed out somewhere, (can't recall), the PRIM failure on the QF A330, which did cause a violent manoeuvre (but did not break or damage the airframe) was not the same failure as was recorded in the series of ACARS messages. While I am not qualified to say that ADC failure would not behave similarly and move flight controls violently, would an ADC system failing in designed-for manner command airframe-breaking control deflections? Regarding the limitation on the actual rudder, vice the pedals, I believe the rudder itself is limited but it will take some time go go through the documents and manuals I have to determine same. I know there have been discussions on various aspects of this limitation in the other thread.
My one question, and I must emphasize that this and all comments regarding what happened after the loss of control are, for me, far less important than what caused the loss of control in the first place; I realize that structural break-up may be part of the latter point but given intact cabin material, some of it pristine, I question any high-speed scenario which also includes the loss of the VS before impact.
That is the fine thing about this forum. Informed and thoughtful participants bring their theories for others to respond to and we get to think on things we had heretofore possibly never considered.
PJ2
Thanks for your input and observation. Your posts on PPRuNe may not be many but they are worth reading. I may have some B777 questions for you.
With loss of the VS, (I am imagining your scenario at high altitude, not lower down) I wasn't thinking a longitudinally stable trajectory as a scenario in a high speed descent - it isn't possible without lateral stabilization. I would expect strong roll due to yawing, loss of the engines due yaw/roll and a high speed descent of what remained of the airplane. For me, the parts that remained of the cabin structure, (from cockpit to rear galley) either indicated an intact-fuselage as described in the BEA report or a mid-air break up of the fuselage. Perhaps your scenario, (low speed descending spin after loss of the VS at high altitude, I think?) may have obtained. I don't think so, but that doesn't matter; as with every scenario, it is at this point where we must wait.
As far as AA587 goes, I know there is substantial controversy regarding the conclusions and reasons for the loss of the vertical stabilzer and that APA has provided significant input. My thinking and therefore my opinion on the design of the AI VS is unimportant as I am not an engineer and cannot validate design. I believe however that this fashion of attaching the VS to the fuselage is the way it is done throughout the industry.
Regarding use of the rudder, I can offer the following:
I have to say that I knew very early on that use of the rudder on a jet transport was discouraged except to keep the aircraft straight during an engine failure and to align the aircraft with the runway in de-crabbing during a cross-wind landing. Otherwise one kept one's feet on the floor.
In the very early 70's, "Jet Upset" did not exist as a concept or a cause of an accident and so was never discussed. In any later (post 2000 or so), jet upset literature we had access to, (we were not, and to my knowledge, still are not, taught recovery from jet upset in the simulator), use of the rudder was specifically warned against.
As a result of all this I would never have expected the use of the rudder in the manner indicated in the AA587 data, not because I thought it might break the VS but simply because one just never did that with the rudder in a jet transport...I never thought there were ever any circumstances in which it was required and while I've certainly experienced wake turbulence at low and cruise alititude, use of the rudder to control the airplane just wasn't a consideration, not from AA587 on but right from the beginning of the career. I think that I wasn't unusual in this understanding.
That said, I wasn't on the flight deck of AA587 so don't know what they faced.
I read with interest both bearfoil's and mm34's input, especially the notion of a sacrificial rudder vs the loss of the VS. The merits of such notions may already be under examination, we don't know.
In the event of a compound ADC failure, all bets are off as to control gain and FBW stability systems, and the potential in moderate severe turbulent conditions to result in a control system initiated structural failure remains possible. This is not limited to pilot only control inputs, as the FBW system would until reverting to direct law be acting in 2 channels to retain attitude. Whether this did in fact occur to 447 remains an open question, but is probably inconsistent with the BEA's observation of a failure of the VS/rudder on water impact. I personally find that opinion, and the available data inconsistent, suspect that the loss of data airborne and the preceding system degradations indicative of structural failure airborne, with VS separation a potential consequential failure following the ADC and turbulence encounter.
My one question, and I must emphasize that this and all comments regarding what happened after the loss of control are, for me, far less important than what caused the loss of control in the first place; I realize that structural break-up may be part of the latter point but given intact cabin material, some of it pristine, I question any high-speed scenario which also includes the loss of the VS before impact.
That is the fine thing about this forum. Informed and thoughtful participants bring their theories for others to respond to and we get to think on things we had heretofore possibly never considered.
PJ2
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Can we draw breath here in lomapaseo's 'dance', and perhaps mm, who's contribution here has been superb!) could save me treading loads of pages and refresh us on the locations/distance apart of the tail empennage and the other debris? This 'in-flight separation' which is being toted here would most likely produce a wide separation, would it not?
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There are two airbus water impacts that I know of where the VS has floated free - 888T off Perpignan and 447. In the former case there is no evidence of a VS detachment and witnesses to the (intact) impact. In the case of 447 there are no witnesses, but finding the VS floating free doesn't mean it came off before impact (as 888T proves)
The failure mechanisms shown by the recovered VS in 587 and 447 are also different. 587 failed as the VS was torn from the mountings, whereas in the 447 case, those same mountings were ripped out of the rear fuselage with the VS. I haven't been able to find good photos of 888T VS, but what there is seems to show it looking more like 447 than 587 (as in detached with parts of fuselage).
To me, none of this proves the VS was still attached at impact, however it does point in that direction, and there is no evidence pointing to it detaching at altitude - at the moment that remains conjecture.
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Can we draw breath here in lomapaseo's 'dance', and perhaps mm, who's contribution here has been superb!) could save me treading loads of pages and refresh us on the locations/distance apart of the tail empennage and the other debris? This 'in-flight separation' which is being toted here would most likely produce a wide separation, would it not?
VS is the yellow diamond. See also page 37 of the first BEA report, and also annex 4 of the same. In short - VS was found in the debris field, not separated. The wide spread of debris in the overall diagram is down to drift due to currents and wind - the spread of items found on each day is less, as would be expected.