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Interesting note about AA Airbus crash in NYC

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Interesting note about AA Airbus crash in NYC

Old 30th Dec 2006, 13:02
  #81 (permalink)  
 
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That T no Sugar fellow is such a wheeze eh? Where did he come from I wonder, central casting for morons perhaps?
As an aside on this issue and I realise it is very unscentific, consider this if you will;
As you drive your car carefully around a slight bend on the icy road, you encounter a patch of ice which upsets your equilibrium; what do you do in response? a: Swing the wheel repeatedly and fully from side to side to try to regain control, or b: squeeze in a bit of into-skid wheel and reduce the power a little?
B gets you home, a gets you in the ditch. Quite simple really.
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Old 30th Dec 2006, 14:09
  #82 (permalink)  
 
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The skidding auto analogy doesn't really hold true, for in the auto there's the highly nonlinear control effect of traction vs no traction. That's why it's important to use the small counterintuitive wheel input to regain traction. (I always seek out an empty icy parking lot to practice this manuver at least once a year!)
The large transport aircraft by contrast has a large yaw inertia, and a relatively linear rudder control system, but may be susceptible to Pilot-In-Loop oscillation in extreme cases. (We used to call it Pilot-Induced Oscillation, but today that's considered pejorative). Such oscillations have proven destructive on many occasions.
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Old 30th Dec 2006, 14:13
  #83 (permalink)  
 
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BEA's reasoning in its commentary posted by GlueBall is viable as far as it goes.

But there is one giant piece of data missing from the report that left this opening for BEA; namely, a recreation of the accident scenario up to the first rudder pedal movement in the second 747 wake encounter-- definitely lets not do more than one.

If Airbus is that confident of its engineering, why did it not arrange for such a test?
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Old 30th Dec 2006, 14:33
  #84 (permalink)  
 
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Barit1 says that the skidding car analogy doesn't hold true then goes on to show that it is as close an analogy as you need to understand the difference between a controlled reaction to the initial upset and the Co-Pilot Induced Ocillations, which resulted in the destruction of the aircraft. I am not a physicist, merely a pilot so the skidding car does it for me, thank you.
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Old 30th Dec 2006, 15:33
  #85 (permalink)  
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This fin exceeded regulatory requirements by very healthy margin
… Airbus composite fins and rudders in general … or this particular (repaired) fin?
.
… in any event … are the ‘regulatory/certification requirements’ reasonable in that case??
.
… surely one must consider ‘possible’ rudder induced side load/s on the fin and attach points when paired with side load from inertial yaw forces + the H-M interface of 1.2 inches of pedal travel at 250kt??
.
… in turbulent wake, is 1.2 inches really giving pilots a fighting chance of achieving fine, targeted rudder effect ..which in turn might help avoid PIO’s??
.
.. common sense suggests the formular in a crude sense is:-
.
- provide enough surface and structural strength to enable management of required/possible flight envelope (then add margins)-
- limit control input parameters to protect the structure whilst providing necessary control authority to the pilots for 'unusual' encounters!
.
This should apply to all combinations of composite or alloy structures irrespective of control method (hydro-mechanical and/or fly-by-wire)
Perhaps metal would bend before breaking,
.. anyone aware of a ‘wake fin off’ accident with a wing slung alloy machine??
but that would be hardly helpful.
.. what .. damaging a metal fin/rudder (whilst retaining it on the airframe) would give a crew less of more chance of a safe return that the whole thing breaking off?? …
.
.. besides, if the initial aileron movement is indicative of the strength of the wake, the vortex may have clobbered the side of the fin/rudder in any number of directions over the elapsed time of the upset encounter ... is it therefore reasonable to expect pilots to provide a physical foot input of 'less' than 1.2inches in either direction whilst counteracting what they may well feel as substancial yawing (perhaps in more than one direction in quick sucession) effects!?
.
.. it is possible that if the aircraft encountered the wake climbing from beneth, the fin would be affected first and from one side (as a result of the rotational vortex stream), then if the aircraft was climbing at a greater rate than the aircraft ahead causing the wake, it would not take long for the fin to receive reverse side force from the upper area of the rotational horizontal wake vortex!
.
.. either way (weakened or not) .. and irrespective of the training and informed best intentions of pilots .. the question remains in my mind..
.
.. could any A300-600 airframe/pilot/turbulence combination result in a similar outcome ..???
.
… 1.2inches …. couple of rudder reversals at slow-ish' speed??
.
… hands up how many folks at the pointy end of these things tend to want to keep their feet up on the glare shield???

Last edited by Scurvy.D.Dog; 30th Dec 2006 at 15:54.
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Old 30th Dec 2006, 15:49
  #86 (permalink)  
 
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Originally Posted by Scurvy.D.Dog View Post
… Airbus composite fins and rudders in general … or this particular (repaired) fin?
This specific fin did not fail until in excess of twice design load, a margin of 33% over the requirement. So even if the repair did weaken the fin, it was still much stronger than it had to be. Which is precisely the basis on which ANY aircraft repair - whether in build or in service - is assessed - "Is it still strong enough to do what's required?"

Originally Posted by Scurvy.D.Dog View Post
… in any event … are the ‘regulatory/certification requirements’ reasonable in that case??
The only means whereby the regulations could be changed to directly address this accident would be to require active envelope protection for all airliners. On a conventional aircraft, where the pilot is the "Flight Control Computer", we rely on his training and airmanship to prevent inputs which risk the airframe structure. The design load manoeuvres required for certification are an ARBITRARY set of cases which have, in practice, proven adequate to provide sufficient structural margin for operations. Since there has been, basically, one event of this type, in who-knows-how-many billion flight hours, it would appear that the regulations are appropriate (the intent of the regulations is not to eliminate risk - that's impossible - but to reduce it to a level consistent with what's perceived as "safe")

surely one must consider ‘possible’ rudder induced side load/s on the fin and attach points when paired with side load from inertial yaw forces + the H-M interface of 1.2 inches of pedal travel at 250kt??
How many such inputs, and at what frequency? Make enough full rudder inputs at close to an aircraft response mode frequency and you WILL break any aircraft of conventional design.

.. common sense suggests the formular in a crude sense is:-
.
- provide enough surface and structural strength to enable management of required/possible flight envelope (then add margins)-
- limit control input parameters to protect the structure whilst providing necessary control authority to the pilots for 'unusual' encounters!
This is exactly what the A300 has: structure that didn't fail until it exceeded the regs by 33% (there's your margin), an RTL to protect the structure from excessive inputs AND enough rudder to meet the various regs for trim requirements.

The simple fact is that the only way to restrict control authority such that no-one can break their aircraft, whatever they do, is to either detach the pilot entirely from the controls, or to so limit authority as to make the aircraft almost unmanoeuvrable. Or make the structural design requirements so stringent it's too heavy to take off.
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Old 30th Dec 2006, 16:21
  #87 (permalink)  
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This specific fin did not fail until in excess of twice design load, a margin of 33% over the requirement.
… design load … do you think the design load is right then?
.
.. 1.2inches of pedal a couple of times in wake and it failed!
the intent of the regulations is not to eliminate risk - that's impossible - but to reduce it to a level consistent with what's perceived as "safe")
… 1.2inches … full deflection .. wake reversals … 250kts … and it failed unsafe!
How many such inputs, and at what frequency? Make enough full rudder inputs at close to an aircraft response mode frequency and you WILL break any aircraft of conventional design.
.. such inputs as 1.2inches or less and a small number of reversal cycles?
.
.. that does not amount to full pedal left and right continuously in other types does it?
This is exactly what the A300 has: structure that didn't fail until it exceeded the regs by 33% (there's your margin),
… AH.. the ‘reg’s’!
an RTL to protect the structure from excessive inputs
.. sorry, I must have missed how that worked in this case?
AND enough rudder to meet the various regs for trim requirements.
… and one would assume asymmetric envelope?!
…. The amount of rudder and its resultant authority is not at issue …. It is the rudder attach, the fin and the fin attach structural resilience to a part of the flight envelope that would not be too difficult to reproduce! ...... that has my full attention!
The simple fact is that the only way to restrict control authority such that no-one can break their aircraft, whatever they do,
... thats is not what I am pondering ... again, is this such an unlikely or agressive reaction to a wake encounter??
is to either detach the pilot entirely from the controls, or to so limit authority as to make the aircraft almost unmanoeuvrable. Or make the structural design requirements so stringent it's too heavy to take off.
… let’s not be silly!
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Old 30th Dec 2006, 17:53
  #88 (permalink)  
 
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Originally Posted by Scurvy.D.Dog View Post
… design load … do you think the design load is right then?
Yes, obviously I do, on the basis that inflight structural failure as a result of pilot inputs is Extremely Improbable. The regulations for this aspect of the design are "as safe" as any other regulation. Absolute safety is NOT the goal.

The 1.2 inches is actually irrelevant, since no-one's flying by pedal deflection. Compare force levels if you like, but pedal travel is pretty much secondary. And, yes, the A300 pedal force to rudder deflection gradient is pretty low, but it's by no means the only type with that characteristic. I suspect that +/-45lbf inputs would cause problems on any type with sufficient reversals.

The regulations are all we have to work with; no-one's going to start designing to arbitrarily higher targets, and in any case the regs ARE good enough in this case.

The RTL would have worked against the design case conditions - and who knows how large an input might have been applied if no RTL had been here in this case? It did what it could, and what it was designed to do; but it couldn't do enough to save the structure.

I'm not being 'silly', I'm pointing out that the practicality of aircraft design is that we accept risk every single flight, due to myriad causes. We simply cannot make the sturcture proof against all possible loading; we can't provide redundancy against every failure scenario. All we can do is achieve acceptable risk - currently about one hull loss per ten million FH - and accept that, sadly, one is greater than zero.
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Old 30th Dec 2006, 18:33
  #89 (permalink)  
 
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Originally Posted by Scurvy.D.Dog View Post
… anyone aware of a ‘wake fin off’ accident with a wing slung alloy machine?? ...
There are photos around of a SAC B-52 (early model) with most of the fin & rudder gone - she landed safely at a N. Michigan AFB (Kincheloe?) around 1960. I don't recall it being wake induced, though.
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Old 30th Dec 2006, 19:27
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Originally Posted by RatherBeFlying View Post
If Airbus is that confident of its engineering, why did it not arrange for such a test?
Probably because they were not invited to. In any case, the only precursor for such an event would be the 737 rudder / 727 wake encounter tests that were performed in the lee of the USAir 427 accident. In that case, the 727 was provided by the FAA and the 737 from USAir upon request from the NTSB. The manufacturer (Boeing) was not involved directly in that experiment.
Originally Posted by Scurvy.D.Dog View Post
… Airbus composite fins and rudders in general … or this particular (repaired) fin?
If anything, the only thing that the repair may have changed in this incident is the point at which the vertical stabiliser failed, in this case the rear rather than the front (where the repair was made) - Given the little I know about air resistance and centripetal force, I'd say it would probably have failed where it did regardless of the repair.
what .. damaging a metal fin/rudder (whilst retaining it on the airframe) would give a crew less of more chance of a safe return that the whole thing breaking off?? …
Depends entirely on the failure mode. I believe that it would have made little difference what the rudder was made of if the design was the same, and a similar design has been good enough for the 767 and 777.
I don't think the B52 incident is a fair comparison as the failed vertical stabiliser lay flat over the horizontal and was of a different (split-rudder) design.

Finally, I'd like to repeat the point made in the link I posted, which is it is a crying shame that the incident has caused more response in terms of territorial disputes (pilots/airline vs. manufacturer, US vs. Europe) than it has in terms of co-operation to reduce or eliminate the chance of a similar failure occurring again.

Other aircraft made on both sides of the Atlantic (and Channel for that matter - Concorde was susceptible to partial vertical stab failure, and the vertical stab was built by BAC) have required special handling due to a design feature (the 737 required a faster approach speed while the ECU installed was of original design, for example), and other aircraft have been designed to reduce operating costs by reducing weight. The A320 which offended a certain breed of pilot for potentially endangering their job has no fewer guys in the sharp end than the 737, 757, 767 and 744 - and none of its envelope protection, which supposedly 'wrote the pilot out of the cockpit' prevents evasive maneuvres in an emergency.

In short, blowing hot air based on supposition and pride makes none of us safer and can in fact make things more dangerous, and if proof of that is needed, all we need do is think of the late Captain Stanley Key.

Last edited by DozyWannabe; 30th Dec 2006 at 19:44.
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Old 30th Dec 2006, 20:08
  #91 (permalink)  
 
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I'd like to ask future contributors to this thread to read NTSB report before contributing, thank you. It might help with improving signal-to-noise ratio.

If you're just reading this thread and wondering WTH was all rant in previous posts about, let me clear some misconceptions: AA587's fin wasn't ripped off by wake turbulence, it didn't fail because it was too weak and it wasn't rudder input alone that tore it either. It failed because of overload which was caused by massive sideslip and rudder deflection. Sideslip was created by rapidly alternating rudder movements. Examination of wreckage, FDR data, witnesses and airplane characteristics lead NTSB to conclusion that rudder input was commanded by PF, and not a result of control circuit failure.

Fact that American Airlines' Advanced Manuevering Programme was given FlightSafety award five days before the accident is quite ironic. Couple of posters are correct in noting that it never advocated alternating rudder inputs and always taught that rudder inputs should be smooth and coordinated but here's wher the problem lies. AAAMP's notion that rudder should be, under some circumstances, be used as primary flight control caused mr. Boeing and mr. Airbus to go apoplectic as this was one use of the rudder they never envisaged on airplanes they've made.

On a personal note I'd like to give you a qoute very fitting for this sad case:
Whenever we talk about a pilot who has been killed in a flying accident, we should all keep one thing in mind. He called upon the sum of all his knowledge and made a judgment. He believed in it so strongly that he knowingly bet his life on it. That his judgment was faulty is a tragedy, not stupidity. Every instructor, supervisor, and contemporary who ever spoke to him had an opportunity to influence his judgment, so a little bit of all of us goes with every pilot we lose.
This is from http://www.skygod.com/quotes/safety.html Don't be put off by a cheesy URL, the site is a real gem.
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Old 30th Dec 2006, 22:24
  #92 (permalink)  
 
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Clandestino and the Scientist make good points. I quite agree that the fin in question was put beyond its design limits - and that it was stressed beyond its required limits. Indeed, its probable that any tail would have failed in such loads. (remember the Mt Fuji BOAC Boeing 707 side wind rotor fin failure?) .

In my posts all I wanted to do was raise the issue of what made it fail - in the light of subsequent events after AA587 - as opposed to events and knowledge at that time. This is a separate issue to what occurred and the limits applicable and performed to in structural terms.
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Old 30th Dec 2006, 23:23
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F/O obsessed with wake turbulence; kicking rudders on previous flights...

Upon viewing the NTSB accident simulation video, it is obvious that the F/O had made overly aggressive and rapid aileron and rudder control inputs; ...a demonstration reminescent of a kid at play at a video arcade game.
"...[NTSB] Pilot Interviews Regarding the First Officer: An American Airlines captain who flew several times with the first officer on the 727 (when they were a junior captain and junior first officer, espectively) told Safety Board investigators that, during one flight sometime in 1997, the first officer had been “very aggressive” on the rudder pedals after a wake turbulence encounter. Specifically, the captain indicated that, when the airplane was at an altitude of between 1,000 and 1,500 feet, the first officer “stroked the rudder pedals 1-2-3, about that fast.” The captain thought that the airplane had lost an engine and was thus focused on the engine instruments. The captain stated that he then asked the first officer what he was doing and that the first officer replied that he was “leveling the wings due to wake turbulence.” The captain, who had his feet on the rudder pedals, thought that the first officer had pushed the rudder to its full stops.
The captain did not recall what type of airplane the 727 was following. He thought that the wake turbulence encounter required only aileron inputs to level the wings but did not think that the first officer had made any such inputs during the encounter. The captain recalled being startled by the first officer’s rudder inputs and indicated that they did not level the wings but created left and right yawing moments and heavy side loads on the
airplane. He further indicated that the first officer did not need to be so aggressive because the 727 was “a very stable airplane.”
According to the captain, he and the first officer discussed this event later in the flight. The captain pointed out to the first officer that his use of the rudder pedals was “quite aggressive,” but the first officer insisted that the American Airlines Advanced Aircraft Maneuvering Program (AAMP) directed him to use the rudder pedals in that manner. The captain disagreed with the first officer and told him that the AAMP directed that the rudder was to be used at lower airspeeds. The captain told the first officer to review the AAMP when he returned home and to be less aggressive on the rudder pedals when they flew together.
American Airlines records indicated that the flight occurred during a 3-day trip sequence from August 31 to September 2, 1997.
...on a subsequent flight, the first officer modified his wake turbulence maneuver; specifically, the first officer used the rudder during the encounter but did not push the rudder to its full stop. The captain added that the first officer was still “very quick” on the rudder. The captain stated that he did not document or report this event at the time that it occurred. The captain further stated that he remembered the event with such clarity because he had never seen any pilot other than the first officer perform this maneuver.
The flight engineer who flew with the captain and the first officer during the 1997 trip sequence recalled that the captain and the first officer had a discussion regarding piloting skills but added that he was not part of that conversation. The flight engineer indicated that he did not recall anything remarkable (such as a yawing event associated with wake turbulence) that would have provoked the discussion. The flight engineer also indicated that the first officer did not discuss the incident with him but that the captain
made a “passing comment” to him about the incident after the flight.
The flight engineer did remember a different event involving the first officer that he thought also occurred sometime in 1997. Specifically, the flight engineer and the first officer (the flying pilot) were on final approach (about 7miles from the runway) in instrument meteorological conditions to LaGuardia International Airport, New York, when a Boeing 737 ahead of their 727 performed a go-around. The 727 encountered the wake from the 737. The flight engineer thought that the airplane rolled as a result of the wake encounter but that the bank angle did not exceed 30º. The flight engineer stated that the first officer made a “fast” decision to go around because of the wake. The first officer called for maximum power without “discussion or hesitation.” The flight engineer explained that the airplane’s tail went down as the nose of the airplane pitched up. The flight engineer stated that the go-around felt “weird” but that the first officer “flew the airplane to do what was necessary to keep the airplane under control.” The flight engineer
also stated that the event happened when the airplane was at an altitude of between 3,000 and 5,000 feet above ground level (agl) and that the airplane was not in immediate danger of ground contact. In addition, the flight engineer stated that the event was one of the more memorable ones of his career. The captain indicated that the first officer’s aggressive response to wake turbulence was out of character. Specifically, the captain described the first officer’s overall flying skills as “excellent” and did not recall aggressive movements or abnormal rudder inputs during other trips with him..."
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Old 31st Dec 2006, 01:04
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Originally Posted by barit1 View Post
There are photos around of a SAC B-52 (early model) with most of the fin & rudder gone - she landed safely at a N. Michigan AFB (Kincheloe?) around 1960. I don't recall it being wake induced, though.
Here's a link:
http://www.barksdale.af.mil/news/story.asp?id=123024862
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Old 31st Dec 2006, 01:15
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Originally Posted by Clandestino View Post
I'd like to ask future contributors to this thread to read NTSB report before contributing, thank you. It might help with improving signal-to-noise ratio.
If you're just reading this thread and wondering WTH was all rant in previous posts about, let me clear some misconceptions: AA587's fin wasn't ripped off by wake turbulence, it didn't fail because it was too weak and it wasn't rudder input alone that tore it either. It failed because of overload which was caused by massive sideslip and rudder deflection. Sideslip was created by rapidly alternating rudder movements. Examination of wreckage, FDR data, witnesses and airplane characteristics lead NTSB to conclusion that rudder input was commanded by PF, and not a result of control circuit failure.
Finally! A voice of reasoned professionalism. Thank you, sir!
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Old 31st Dec 2006, 01:19
  #96 (permalink)  
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.. have read the report!
.
.. a couple of quotes from your link
Take nothing for granted; do not jump to conclusions; follow every possible clue to the extent of usefulness . . . . Apply the principle that there is no limit to the amount of effort justified to prevent the recurrence of one aircraft accident or the loss of one life.
.
— Accident Investigation Manual of the U.S. Air Force.
.. thus my questions above!
I am a history major. I believe that the past is prologue. The archives bear that out. Most major aircraft accidents are not acts of God. In our recommendations we try to take what we have learned and correct situations so it shouldn't happen again.
.
— James Hall, NTSB, 1996.
.. so what is happening to prevent a reoccurrence .... training pilots not to use rudder to correct perceived yaw/roll in wake conditions??
.
.. aircraft control systems/sensitivity and structure are all A OK then I assume?!
.
.. anyhow, over to the experts ...
.
... I hope 2007 is a safe and happy year for us all!
.
Cheers
.
Scurv
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Old 31st Dec 2006, 04:37
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after reading everything about this sad accident I call upon the NTSB to properly admonish the FAA and demand changes to enhance safety.

The FAA certified the aircraft and its manual(POH)

The FAA certified the airline operating the plane

The FAA certified the airline's training program

The FAA certified the pilot. And along the pilot's career had the opportunity to test the pilot's knowledge of rudder inputs and their effects many times...written and oral exams for the private, commercial, instrument rating, multi engine rating , airline transport pilot certificate and perhaps others including type rating.


regarding the SAC B52 incident, I think there was one another one due toloss of vertical fin leading to a crash somewhere near Cumberland Maryland about 45 years ago or so. I'll bet the pilot didn't rock the rudder!
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Old 31st Dec 2006, 04:57
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Originally Posted by bomarc View Post
after reading everything about this sad accident I call upon the NTSB to properly admonish the FAA and demand changes to enhance safety.
The FAA certified the aircraft and its manual(POH)
The FAA certified the airline operating the plane
The FAA certified the airline's training program
The FAA certified the pilot. And along the pilot's career had the opportunity to test the pilot's knowledge of rudder inputs and their effects many times...written and oral exams for the private, commercial, instrument rating, multi engine rating , airline transport pilot certificate and perhaps others including type rating.
regarding the SAC B52 incident, I think there was one another one due toloss of vertical fin leading to a crash somewhere near Cumberland Maryland about 45 years ago or so. I'll bet the pilot didn't rock the rudder!
Ok, now that we have our aviation safety problem solved guess we will be traveling by trains and automobiles for quite some time.
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Old 31st Dec 2006, 17:24
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Originally Posted by Scurvy.D.Dog View Post
so what is happening to prevent a reoccurrence .... training pilots not to use rudder to correct perceived yaw/roll in wake conditions??
.
.. aircraft control systems/sensitivity and structure are all A OK then I assume?!
Well, amongst other things that have happened (references are to the NTSB recommendations in the accident report)...

All the OEMs have put some kind of warning about excessive control use in their flight manuals, I believe.(A-04-59)
Pilots are now, I hope, much more aware that control inputs below VA are not necessarily within the design envelope. (A-04-60)
The AA training programme was, I believe, reviewed.(A-04-61/62)
All the major manufacturers were asked (required?) to check their structure against manoeuvres more like the AA587 one (rudder doublets)
NTSB (or FAA? - I forget) has been requesting info from all the OEMs regarding rudder system characteristics.(Those last two for A-04-56 and -57, I believe)

So it is conceivable that a change to the regulations will eventually be forthcoming, though I expect it will be concerned with issues of control sensitivity, not the structural design criteria.
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Old 31st Dec 2006, 18:03
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Originally Posted by Mad (Flt) Scientist View Post
So it is conceivable that a change to the regulations will eventually be forthcoming, though I expect it will be concerned with issues of control sensitivity, not the structural design criteria.
Control sensitivity is at the heart of this incident. I'd hope the regulations require a design similar to what the newer (757/767/777) Boeing's have. From a human factors POV using that rudder design makes sense. That, coupled with a lower sensitivity rate, should be the 'Gold Standard' of a/c design.
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