Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Interesting note about AA Airbus crash in NYC

Tech Log The very best in practical technical discussion on the web

Interesting note about AA Airbus crash in NYC

Old 28th Dec 2006, 15:09
  #61 (permalink)  
 
Join Date: Dec 2006
Location: the Metroplex
Posts: 12
Thank you Slats One.

I have long held that there are only 2 pilots who know what it feels like to have the tail come apart on an Airbus and they are both dead.

The NTSB has only 2 kinds of accident findings:

1. Pilot error and the guilty pilot is alive.
2. Pilot error and the guilty pilot is dead.

587 is the latter.

During the investigation of the 587 crash, President Bush was trying to form coalition to fight the GWOT. Whatever else it is, the NTSB is a political animal.

There were 3 things in play during the NTSB investigation into this crash.

1. Politics – The US didn’t need to upset the EU by finding Airbus at fault for manufacturing or certification reasons, thereafter causing the grounding of an entire fleet, perhaps worldwide.

2. Money – The NTSB didn’t want to frighten any more customers away. The US airline industry advance bookings after 911 we non-existent.

3. Pilots – What did the guilty [email protected](s) do wrong?

Who do we think is going to win that battle? If you think it’s the pilots, go to the rear of the line. Politics and money trump pilots every time in any NTSB investigation.

So the easy fix was to blame a dead pilot. No political ramifications, very minor economic ramifications and one dead pilot who can’t tell what really happened.

Over and out, as far as the NTSB is concerned.
Jurassic Jet is offline  
Old 28th Dec 2006, 17:24
  #62 (permalink)  
 
Join Date: Mar 2006
Location: wiltshire uk
Age: 57
Posts: 85
Ageing composites- more

Glad I am not alone. I do not do conspiracy theories, but the trail of events post this crash is begining to look iffy.

One other point, they found the tail fin minus the rudder -has anyone determined if the rudder came off after the fin snapped - ie as the rudder fell, or did the rudder come off prior to fin failure?

Given that the rudder is not attached to the fuselage -but to the fin - surely it's point that should be answered-ie which wagged the dog first?

As far as I am aware, there is has been no debate as to why the fin was found minus the rudder and when did the rudder come off that fin?

If you study the CVR tape it is very clear that before the application of full power -and before the sound of what might be the fin coming off. there is clearly a handling issue apparent- with reactive process from the PIC and left seater (verbal inputs). What casued that handling issues- was it relly just wake turbulence and pilot input. I doubt it.

(And if it was, that means that the generic tail design as fitted across a range of aircraft is now suspect - an entirely separate issue based on the acceptance of the NTSB findings -not the questioning of it some of now make..)

The political and financial issues as cited are of course relevant -but are not to me the fulcrum. The fulcrum- the point of the thing is that rudder and subsequent events to several aircraft - notably Transat - have not been adequately invesitgted at teh time or consequent to further events.

Nevile Shute and Ernie Gann would have worked on this one.

After careful consideration, I now doubt the accepted NTSB version of events: clearly I am not alone. The AA 587 pax and crew desrve the truth - whatever the ramifications... Time will tell.
Slats One is offline  
Old 28th Dec 2006, 17:52
  #63 (permalink)  
 
Join Date: Jan 2006
Location: US
Posts: 1,976
Spent the morning going over the AAMP tapes. Dated 19 Dec 1997. Training for the CA on AAMP was in May 1997 with sim training 1997(tape presentation was from March/April 1997-NTSB report pg 85 - pg 99 out of 212 pdf file) so

It's an excellent presentation. I'm no fan of the presenter but his briefing is on target. It's about operations at the edge of the flight envelope to save a/c and is about typical line operations. Discussion centers on the to roll the a/c from nose high attitudes and the ability to use the rudder if necessary.

He refers to rudder use several times and it's always 'coordinated', 'smoothly', 'these are powerful rudders so use small amounts', 'I never said to use opposite rudders', 'if you want to use a little rudder go ahead', etc, etc.

http://www.ntsb.gov/publictn/2004/AAR0404.pdf

The NTSB report deals with the AAMP on pages 80 (pg 94 of pdf) Sec. 1.17.1.2 until pg 95 (pg 109 of pdf)

Page 95, (pg 109 of pdf) Sec. 1.17.2.2.1 has Airbus' discussion of the use of rudder. The difference between what Vandenburg's entire presenation, and Airbus' position, is trivial. Airbus had concerns about Vandenburg's comment to use 'rudder in the direction you want to roll'. I thought 'uh oh' when I saw that part of the tape. But when Vandenburg's total presentation is viewed the one sentence being called into question is nit picking. The total presentation mentions several times the limited use, coordinated, small, and careful use of rudder. And, to satisfy the manufacturers concerns, at the end of the tape he mentions the limitations to rudder use again(NTSB report).

If you can't view the AAMP tapes at least read the report. AAMP is still taught at AA training. The briefing by CA Vandenburg is still valid.

And even a non professional pilot on the NTSB gets it (previously posted quote) -

While the board issued recommendations in early 2002 for pilots to be cautioned in training about the dangerous potential for rudder reversals (see ASW, Feb. 18, 2002), Vice Chairman Rosenker said, "At this point, we haven't done much about the rudder - its sensitivity."
Board Member Debbie Hersman said, "The sensitivity is more important than the AAMP program."

The A300 rudder is the most sensitive rudder out there.

And the investigaton shows that the plane moved in response to the rudder inputs as opposed to side loads generating first followed rudder inputs to stop the unintended yawing moments.

As Mad(flt)scientist said, any commercial a/c not protected by computer flight laws can generate these loads. That folks argue or doubt this today is scary.
misd-agin is offline  
Old 28th Dec 2006, 18:13
  #64 (permalink)  
 
Join Date: Jan 2006
Location: US
Posts: 1,976
Originally Posted by Slats One View Post

If you study the CVR tape it is very clear that before the application of full power -and before the sound of what might be the fin coming off. there is clearly a handling issue apparent- with reactive process from the PIC and left seater (verbal inputs). What casued that handling issues- was it relly just wake turbulence and pilot input. I doubt it.
I had the luxury of talking with someone who knew about folks reactions from when they flew the accident profile in a NASA sim.. Said folks were sceptical of blaming the rudder inputs for the crash. Problem is typical simulators don't do an accurate job of simulating the side loads. The NASA simulator does a better, if not great, job of simulating side loads.

Simulation timeline is running - "Ok, little bit of turbulence...first rudder input now... WOW *HIT! Folks were stunned by the side load generated.(try flying with a G meter and putting a 1/4 or larger G load on the a/c quickly. Now make that a side load. I was told it was very abrupt).

I was told this is when (some?) folks realized it might have been a rudder PIO. This is the rudder sensitivity the NTSB board discussed.

misd-agin is offline  
Old 28th Dec 2006, 18:18
  #65 (permalink)  
 
Join Date: Jan 2006
Location: US
Posts: 1,976
Originally Posted by bubbers44 View Post
Slats one, I have always thought your feeling that he was reacting to the aircraft yawing because the vertical stab or rudder was failing was correct. Did they study if the rudder inputs were before or after the aircraft yawed? I believe I read that the actuators on the rudder sends signals to the flight recorder, not the rudder pedals.

http://ntsb.gov/Events/2001/AA587/board_mtg_anim.htm

"Flight Path Animation" shows relationship between rudder position and lateral loads so yes, they did study that.

3 rudder swings in 3-4 seconds, followed by full right rudder for two seconds, followed by 2 more rudder swings in two seconds. It's at the end of this 7-8 second timeframe, that included 5 full rudder movements, where data acquisition from the rudder position failed(fin departed).
misd-agin is offline  
Old 28th Dec 2006, 18:23
  #66 (permalink)  
 
Join Date: Apr 2005
Location: Southeast USA
Posts: 802
Hey … guys … ! I am not a dyed-in-the-wool, NTSB fan (as I DO think they make their share of mistakes, like every human being), but I think they got this one right. Everyone here seems to be trying to attribute a single cause to a very complex series of events that resulted in a huge tragedy. THAT simply isn’t going to happen. Those of you who have been involved in aviation for a reasonable period of time should easily recognize that any story is going to have multiple parts – some good, and some not-so-good. That is true here as well.

Those of you who believe the F/O of AA587 was prematurely taken to the woodshed because he is no longer here to defend himself – are partially correct … but only partially. He WAS at the controls. Therefore, he has to bear the responsibility for the control input … but, before you dismiss me out-of-hand, I think he had plenty of help in getting to the accident site.

Those of you who believe it was the faulty, composite aircraft assembly, you may have some legitimacy in your concerns, but none of it has been proven. So, I’m afraid you’ll just have to hold on to your theories for a while.

Those of you who believe it was the faulty design of this particular aircraft, DO have some legitimacy in your concerns – but only some. Read below.
Those of you who believe that it was AA training that should absorb the brunt of the “fault” also have some legitimacy – but, you too, get only some legitimacy.

Those of you who believe that it was Air Traffic’s fault, clearing AA for takeoff too closely behind the heavy JAL B-747 … unfortunately, your concerns get only “honorable mention,” because, while encountering wake turbulence was involved and (I think) was the initiating catalyst, it did NOT cause the accident.

Here is a link to an animation derived from the Flight Data Recorder that shows an animation of the aircraft (although that isn’t the most interesting part, in my opinion), the time, altitude, airspeed, attitude indication, control wheel position (roll control position and pitch control position), vertical acceleration, rudder pedal position (L/R deflection), rudder surface position (also L/R deflection), lateral acceleration and a top-down view animation of the vertical fin/rudder position.

http://www.ntsb.gov/Events/2001/AA58...path_web01.wmv

In this particular circumstance, the airplane is known to have a very sensitive rudder control input system – and one that gets a maximum rudder deflection, not only lighter in feel than other airplanes, but also with a lot less pedal travel required to get a greater amount of control surface deflection. Specifics? The A300-600 rudder is hydraulically actuated with no direct feedback to the pilot. There is no “air load” on the control surface that the pilot can “feel,” so the system is built to provide and artificial “feel.” By way of comparison, a B-767 (a similar sized airplane) at 250 knots has a breakout force of 17 pounds-feet (force necessary to begin movement) and the pilot would need to generate 80 pounds-feet to achieve maximum displacement – which in the B-767, is a bit over 3 and a half inches of rudder pedal travel and 8 degrees of rudder surface deflection. The A-300-600 is noticeably different. With the same circumstances, the pilot has to use 22 pounds-feet to start the movement (breakout force) and 32 pounds-feet to get maximum rudder pedal travel (about 1.2 inches) and maximum rudder surface deflection (9.3 degrees). The math here says that the A-300 is over 7 times as sensitive as the B-767; or, said another way, the amount of rudder actually deflected for each pound of force on the rudder pedal above the breakout force is almost 9 times as much in the A-300 as in the B-767.

We might have had a pilot who was “spring-loaded” to the use of rudder. Specifics? There is the report from other pilots who had flown with this first officer who have said that, in their opinion, he “used the rudder too much.” Now, I certainly don’t know what that means, but, when you combine that statement with a careful review of the FDR animation video, it’s hard not to notice how quickly and how much the rudder was used in this case.

We might have had a training program that instilled in this pilot the idea that the rudder is an effective tool to assist in controlling the airplane. Specifics? While not specifically “damning” in its content (my information is that the specifics in the training program regularly use the terms “smooth,” “coordinated,” “use small amounts,” etc.), the American “Advanced Maneuver Training” course did advocate the use of rudder in recovering from unusual attitudes; and this is not the only instance where an American crew used the rudder (as they were trained to do) in a circumstance that resulted in a flight condition that got the NTSB’s attention.

We had a pilot that, at least to me, appeared to be spring loaded to the “I’d-better-get-into-the-controls-quickly-to-prevent-from-happening-what-I-don’t-want-to-have-happen” position. Specifics? Careful observation of the FDR animation shows almost immediate and rather significant rudder pedal and rudder surface deflection at the very outset of the second set of turbulence encounters – which appear to be applied prior to aircraft displacement. You will have to view the video and make your own determination.

We had a pilot that probably was not aware of the problems that multiple control input and reversals could cause. Specifics? Shoot, there are still pilots on the line who either don’t know, or are skeptical of the fact, that multiple, commanded rudder reversals with an airspeed below Design Maneuvering speed can cause significant airframe damage. Although, with all this publicity, I can’t imagine too many pilots not knowing of this particular accident and its various points and counter-points for very long!

We had a flight that took off relatively close (although probably within legal limits) behind a very heavy, very slow airplane that is known to generate a ton of wing tip vortices, and followed the same departure flight path – below and behind – precisely where wing tip vortices like to live. Specifics? I think this can easily be determined with a review of the CVR tapes and tower and ATC observations.

We had a pilot that probably found himself in a PIO and didn’t know how to correct for it. Specifics? Again, I would refer you to the FDR animation – and again, believe that you will have to determine the accuracy of this statement for yourself.

Also, the comparisons between this accident and the two accidents involving B-737s (for which Boeing has since developed and deployed a “fix” and new procedures) are not valid – as these two circumstances heavily involved the phenomena of “cross-over” speeds vs. aircraft control that had no application to the AA587 accident.
AirRabbit is offline  
Old 28th Dec 2006, 18:57
  #67 (permalink)  
 
Join Date: Mar 2006
Location: wiltshire uk
Age: 57
Posts: 85
composites- final thoughts from slats one

Airrabbit makes a very reasoned case - which should not be overlooked- its the growing snowball effect of course- all those differing factors building up on top of each other.

All i am trying show is that if you view the AA587 NTSB report with the knowledge of post -report subsequent events (ie Transat etc) it becomes clear that subsequent circumstances- had they been fact at the time of AA587, may, repeat may have created a different mindset.

I think the NTSB should perform a deep peer review of what they knew/know then and now- a la Rumsfeld's, known unknowns and unknown unknowns...

I have just looked again at some AA advanced training video- the lecturer is clearly using a T tailed twin jet- Fokker 100 or MD series (?) He advocates use of top rudder to stop the nose falling down (he demonstrates such nose fall). But he never tells anyone to kick it their.

And those baby T tailers are very different beasts - we all know that...

I am still at a loss as to which came first on the AA 587 - the tail wagging the pilot or vice versa- but I now believe that their are enough subsequent events to suggest a review of the finding that it was the pilot- so far promulgated.

Its not what happend its why- but what if the why was because of the what-the unconsidered what at the time (but since highlighted by events)

The rear cabin on AA857 must have been twanging around like a circus ride - how come no commander intervention - how come no thinking about who or what was causing the swing - pedal or fin/ rudder- which happened first.

If we had not had Transat etc since- all this could be dismissed as speculative dross. but it is not - not any more -not now we know what we know...

The arguement that this had not happened before so it cannot be the aircraft is bunkum- becasue that ignores the issue of teh ageing composite - about which even my professor of composites friend says " we know so very little - except from the experiecne of heat and cold soak and chemcial degredation on yachts..."

As I said, its classic Nevile Shute stuff..

Its time others typed, fly safe...
Slats One is offline  
Old 28th Dec 2006, 20:53
  #68 (permalink)  
 
Join Date: Sep 2001
Location: Toronto
Posts: 2,189
Breakout to Maximum Deflection Ratio

Using AirRabbit's numbers for 250 kt:
Type.. B-767 A-300-600
Brkout 17 .... 22
Max... 80 .... 32
Travel 3.5 .....1.2
Max/
Brkout 4.7 ....1.4

I am led to suspect that any attempt to use rudder on the A-300-600 at 250 kt. is highly likely to get maximum rudder

If you looking for an APC/PIO trigger, it's hard to beat this one.
RatherBeFlying is online now  
Old 28th Dec 2006, 23:47
  #69 (permalink)  
 
Join Date: Dec 2006
Location: the Metroplex
Posts: 12
No conspiracy thoughts here either.

In my opinion, it's more like the NTSB decided to ignore Ockham’s Razor.

  • 587 crashed because the rudder failed causing the vertical fin to fail which caused the airplane to crash.
  • 587 crashed because the rudder failed causing the vertical fin to fail because the first officer made excessive and abrupt rudder inputs, which caused the airplane to crash.
The finding of pilot error is just the simplest, cheapest and most expedient way to end the investigation. That it also resolved the political and money problems was just icing on the cake.

JJ
Jurassic Jet is offline  
Old 29th Dec 2006, 04:13
  #70 (permalink)  
 
Join Date: Apr 2005
Location: Southeast USA
Posts: 802
Again - take a look at the link provided with special attention to two areas on the video. The first is between 15:35 - 15:45 (the first wake turbulence encounter) and notice the exclusive aileron control applications in response. The second starts at 15:51 and runs to the end (the second wake turbulence encounter) and notice the aileron, elevator, and rudder applications in response. Notice when they start, how much control input was used each time, and how frequently and how quickly these control applications were reversed.

Here's the link again:
http://www.ntsb.gov/Events/2001/AA58...path_web01.wmv
AirRabbit is offline  
Old 29th Dec 2006, 04:14
  #71 (permalink)  
 
Join Date: Jan 2006
Location: US
Posts: 1,976
Originally Posted by RatherBeFlying View Post
Using AirRabbit's numbers for 250 kt:
Type.. B-767 A-300-600
Brkout 17 .... 22
Max... 80 .... 32
Travel 3.5 .....1.2
Max/
Brkout 4.7 ....1.4

I am led to suspect that any attempt to use rudder on the A-300-600 at 250 kt. is highly likely to get maximum rudder

If you looking for an APC/PIO trigger, it's hard to beat this one.
Story going around AA during the investigation was three pilots, Airbus, AA supvr, AA line pilot(union), were put in the sim for testing. All three were asked to apply half rudder at 250 kts.

Of course the AA pilot and the union pilot, if anyone, would be suspect to perhaps slightly overdo their input to support the incident crew. How about the Airbus pilot? No, he'd baby it, if anything, to show how simple using the rudder actually was.

All three applied something like 45 lbs +/-, resulting in full pedal deflection. And they knew in advance how sensitive the rudder is.

The rudder is normal at approach speeds, fine at 210 kts, and significantly more sensitive at 250 kts.

But the design of the A300 is similar to all the older designs except for the 747/757/767/777. I don't know how the A330/340/380 rudders operate. But as AirRabbit's posted data shows what sets the A300 apart from it's peers is the sensitivity of the rudder. 737/727/DC-9's etc. are not as sensitive with the same rudder design.
misd-agin is offline  
Old 29th Dec 2006, 05:01
  #72 (permalink)  
 
Join Date: Jul 2000
Location: Down south, USA.
Posts: 1,588
The DC-9's pedal travel results in a direct, proportionate rudder response, whether powered by a bit of right system hydraulic pressure or (no hydr.)mechanically with the (unlocked) control tab, from what I've always studied.
And the tails have no graphite epoxy or other synthetic, plastic sort of parts.

DC-9s, still flying since 1965, or '72! And no cold-bonding process, as used in the B-737-200 upper fuselage...remember the tragic Aloha Airlines emergency descent, minus one flight attendant?

Why was the A-300 weight reduction in the vertical fin worth the risk of undetected fatigue deep inside the tail? Were not the forecast operating temperature extremes a new element?
Ignition Override is offline  
Old 29th Dec 2006, 05:17
  #73 (permalink)  
 
Join Date: Jun 2001
Location: Surrounded by aluminum, and the great outdoors
Posts: 3,707
I.O sounds like a piece from SNL's old skit "and now a few words from and angry old may" culminating with the statement..."and thats they way it was..and we LIKED it", "and we'd do it again if we had to"
ironbutt57 is offline  
Old 29th Dec 2006, 05:57
  #74 (permalink)  
 
Join Date: Sep 2001
Location: 38N
Posts: 356
Damn Right. They don' makem like they usta. No heft. Can't hammer 'em back into shape when something gits bent.

Take it to mind, tho - Progress doesn't always move us forward.
arcniz is offline  
Old 29th Dec 2006, 19:59
  #75 (permalink)  
 
Join Date: Nov 1999
Location: 31-43,000 feet ALL the friggin' time!
Posts: 68
...Like the Comet.
jeff748 is offline  
Old 29th Dec 2006, 21:21
  #76 (permalink)  
 
Join Date: Jan 2001
Location: UK
Posts: 1,089
"Like the Comet" did not Boeing benefit from the tremendous research that went on to find why the Comets failed and used the results accordingly? Have yet to see any USA built airliners exceed mach1. Is the VC10 not still the fastest sub-sonic airliner ever built?
Not biased but just wanted to set the record straight.
WorkingHard is offline  
Old 29th Dec 2006, 23:36
  #77 (permalink)  
 
Join Date: Dec 2006
Location: washington,dc
Posts: 486
dear working hard:
just to set the record straight, both the DC8 and DC9 were taken to mach 1.0+ during tests...neither had rudder problems.(not that the subject referenced rudder)

as to the others speaking ill of the 737 and its rudder...consider that planes built now would have to have a different rudder system for certification...the airbus is a much newer plane (even the A300) and should be better.

The VC10 is a lovely looking plane. I don't know the speed specs on it. but like the DC9, the rudder is quite small compared to the A300 or the 737. For reasons discussed on this thread before.
bomarc is offline  
Old 30th Dec 2006, 10:48
  #78 (permalink)  
 
Join Date: Mar 2006
Location: wiltshire uk
Age: 57
Posts: 85
The VC10 by the way, flew 3,000 hours at BOAC and nearly 6,000 hours at the RAF with an early composite rudder (1 section of the 3 rudders on VC10) over the course of 3 years. No problems were encountered and along with other trials (like the all composite HS125 wing) these 1970s experiments hastened the use of composites in aviation.

BUT no ageing tests across a decade of temp soak and chemical changes could have taken place in such short trials times. Which again takes me back to my early post- the fact of the ageing composite. Such phenomena is not as rapidly obvious as the Comet's meteal fatigue issues, but it exists.

I did some early work 25 years ago on trying to build an integral (not bolt in) sub-chassis from composite, within a composite skin structure - to create load/stress paths within the panel rather than just have the stuff 'creep' to its nearest weakness and shatter at random.

Yet to this day car makers and our european composite friends just mould a panel and glue or bolt in, composite and alloy reinforcements - which as you can see from the AA587 fin fracture history, does not maketh much sense.

Imagine a fiberglass car- much stronger/lighter than a steel one -but when it does break, it shatters at random and often where you least want it too.. Yachts are still the same.

Here endeth the lesson , but its all vital to the AA587 and subsequent failures - and to the forthcoming 787. I reckon there are lot of worried engineers out there on both sides of the pond...
Slats One is offline  
Old 30th Dec 2006, 11:46
  #79 (permalink)  
 
Join Date: Jun 2001
Location: UTC +8
Posts: 2,613
BEA comments on the report... (NTSB dockets)

(French) BEA comments on the NTSB report entitled:
"An Inquiry into Whether a Pilot-Induced oscillation was a factor in the crash of American Airlines Flight 587".

"...Regarding the general approach:
On section II, « PIO phenomenon », we have no comments on the veracity of what is presented. What may, however, lead to confusion is the choice of the examples and the definitions given.
This section presents a digest of what is known on the subject of PIO, but it should be emphasized that: The two examples selected (the C17 and the Space Shuttle) describe phenomena where the flight control used acts directly on the axis to be controlled (aileron/roll for the C17, control column/pitch for the Shuttle). The main difference with AA587 resides in the fact that, in the latter case, the pilot used rudder control inputs in an
attempt to control roll. The main identifiable cause of time delay between the control inputs and aircraft response is, in this case, the time delay to induce roll. This subject is, however, never examined in this study.
In the following section, a conclusion is reached through syllogism, based on the judgment that there is PIO and that this phenomenon is attributable to the sensitivity of the airplane.s flight controls. This short cut fails to take into account induced roll, characteristic of rudder control, that is common to all transport airplanes in this category, which generates a time delay between the pilot.s control input and the response perceived. The Airbus simulation on the relation between PIO on the roll axis and the sensitivity of the controls appears to show that even a light rudder pedal input may create a divergent output. This system remains stable simply by using the control wheel with high gain.

As far as we know, no studies have been undertaken on PIO on the yaw axis since the rudder is not a primary flight control. It therefore seems important to treat this problem in a global manner, without omitting any elements. The definition of sensitivity applied in this report for the purpose of comparing the
A300-600 with other transport aircraft marks out the A300-600 without being
representative of the handling qualities of the airplane.
To summarize, hypothetical PIO can be considered to be caused by a time delay between the control input and the expected parameter. This time delay is the sum of different elements:

• Pilot response time, which can be broken down into perception time and
reaction time. It is commonly agreed that reaction time is about 0.2 seconds.
As regards perception time and time to analyze the perception, this can be
variable. In fact, this depends on factors relating to habituation. A trained pilot who knows the characteristics of the system well uses short cuts (Rasmussen model, « Skill Based Behavior »).
• The sensitivity of the flight controls, as mentioned in the report. There is,
however, a lack of factual data to characterize the sensitivity of A300-600
rudder pedals and, in general, data on PIO induced by rudder pedal inputs.
• Time delay due to saturation of the servo-controls. The speed of the servo-
controls is about 45°/s for the ailerons and 60°/s for the rudder. This should be compared with other systems.
• Time delay specific to the use of the rudder (induced roll, etc).
Consequently, the approach used in the report, which does not include all of these parameters, cannot be considered as complete. The complexity of these phenomena requires additional precautions to be taken in the presentation of the results.

Comments on section III:
III.B.1: Bearing in mind all of the reservations expressed on this report, it does not appear to us to be convincing to state that the PIO phenomenon has been clearly established just on the basis of observations made on oscillation frequencies. We note that following the first right open loop rudder input there was a first rudder doublet over a period of two seconds, stabilization for two seconds and then a second doublet over a period of two seconds. These observations do not lead to the conclusion that there is a cyclical phenomenon.
It is likely that the pilot reacted to unusual perceptions and that his actions in turn reinforced his perceptions. Given the complexity of the system, with reactions in all three axes, it seems to us difficult to make a simple judgment that the flight controls are implicated. Further, and in accordance with E. Cooper.s warning on the evaluation of an airplane.s handling qualities, only an evaluation carried out with a pilot would make it possible to draw any conclusions on the sensitivity of the flight controls:

At present the applicability of the mathematical analysis including representation of the human operator is restricted to the analysis of restricted task. Since the intended use (mission) is made up of several tasks and several modes of pilot-vehicle behavior, it is difficult first to describe accurately all modes analytically, and, second to integrate the quality in the separate tasks into a measure of overall quality for the intended use. "(G. E. Cooper NASA, the use of pilot rating in the evaluation of aircraft
handling qualities)
III.B.3: sensitivity was defined, by the human factors group, as "magnitude of aircraft motion in response to a given amount of rudder pedal force above the breakout force (simple measure = lateral acceleration in cockpit resulting from the yaw moment)". However, this report uses another definition of sensitivity "A300-600 rudder pedal is more sensitive than Boeing design if you compare the degrees of rudder commanded per pound of pedal force above breakout".
This new definition of sensitivity cannot be taken into account as a significant factor, since an airplane with different flight control surface dimensions may have identical sensitivity, even though the reactions felt may be very different. Comparisons with other manufacturers on this basis seem meaningless and inappropriate.
We do not agree with the physiological data described in this study. The size of a muscle has no influence on control sensitivity. Comparisons with helicopter yaw control and automobile brake control would serve to illustrate our point.
III.B.5.a The last phrase contains a short cut that does not satisfactorily establish the relation between rudder/pedal sensitivity and a longitudinal axis PIO. While it is true that uncoordinated actions on the roll and rudder controls may have disoriented the pilot, it is still not proven that the sensitivity of the rudder controls was the initial causal factor.
III.B.5.b The use of these results is surprising. Observations made on servo-control rate saturation can be applied to all aircraft. There is no aircraft on which the servo-controls respond instantaneously. This means that the time delay which is mentioned here is a general characteristic. It is, of course, necessary to take this into account in the study but it would be reasonable to include (as in table 1) the relative position of the A300-600 in relation to other airplanes in the same category and to add that the other airplanes have the same limitations. Thus the time delay which is mentioned for the time delay calculation would apply to any servo-control, and it is worth noting that this time delay is of the order of a half a second. In any case, it has not been proven, on the basis of the FDR parameters, that there was any saturation of the rudder, only of the ailerons.
Comments on section IV: The proposition that the pilot did not use the rudder/pedal implies no PIO does not mean that the sensitivity of the rudder/pedal implies PIO.
The preceding remarks and questions call into question the conclusion of this report. The only source of time delay accepted is the sensitivity of the rudder pedals. By omitting the time delay associated with the induced roll that develops when the pilot uses the rudder pedals, as well as the impact of pilot conditioning on the gain, the topic is examined only partially. It is thus difficult to use this document as it stands in the context of the analysis of this accident. It does, however, provide a springboard for questions that may lead to an understanding of this event...."
GlueBall is offline  
Old 30th Dec 2006, 12:46
  #80 (permalink)  
 
Join Date: Feb 2005
Location: Correr es mi destino por no llevar papel
Posts: 1,384
Regarding the issue of ageing composites, it seems that the composites within the tail of N14053 aged graciously because:

NASA's and Airbus' FEA models determined that failure of the rear main attachment lug was the most probable initial failure. The FEA models and NASA's PFA model also determined that the failure initiated at the final observed maximum vertical stabilizer root bending condition during the accident flight, when the vertical stabilizer was subjected to a global root bending moment of more than two times the value defined by the limit load design envelope. (As previously stated, for certification, the vertical stabilizer is only required to support loads of 1.5 times load limit without catastrophic failure.)
as stated on pages 68 and 69 of NTSB report. Couple of previous pages contain methods applied in analysys of fin and rudder. More of it is in other documents available within public docket. If you're still convinced that there was unprovoked delamination or that fin failure started from the front, please read the report and tell us exactly with which part you disagreee and why.

What difference would made if fin was metal instead of composite? Do you think that it would be beefed up to stand 3 times the load limit? Me not. This fin exceeded regulatory requirements by very healthy margin. Perhaps metal would bend before breaking, but that would be hardly helpful.

Accident investigation is not about approportioning the blame. Goal of accident investigation is to gain understanding of particular accident, so its reoccurence can be prevented. By listing F/O's rudder input as primary contributory cause, NTSB didn't say he was to blame or should get punished, just that he did so-and-so and consequences were such-and-such. Blame and punishment are best left for religious and judicial entities.
Clandestino is online now  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.