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He stepped on the Rudder and redefined Va

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He stepped on the Rudder and redefined Va

Old 30th Sep 2013, 21:51
  #141 (permalink)  
 
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Originally Posted by DozyWannabe
I doff my cap to you for a thoughtful, well-reasoned and insightful post.

One thing I remember from the time was a BBC Horizon documentary that stated a significant number of that FO's colleagues on AA's A300 fleet had transferred to Boeing types because they believed whole-heartedly in the "weak tail" scenario. Such actions speak to camaraderie and loyalty and they are no doubt noble, even if the evidence points elsewhere.

But if we are to be rational about things then we must follow the evidence, even if we don't like where it may lead. Heaven knows I've been accused enough times of "defending" or "protecting" Airbus when sticking to the evidence is all I've been doing. At the end of the day, even with the speculation over why the FO may have handled the rudder the way he appeared to, there is no arguing with the fact that the vertical stab did not fail until the forces on it exceeded the load limit by a factor of 2.2 times, exceeding the Ultimate load reserve by a factor of 1.47 times.
You have, as I think I’ve said before (probably several times), both my respect and my admiration. So, thanks for your comments – and I look forward to reading what you have to say on almost anything, because I’ve long ago recognized that most of the participants here are really after the truth about whatever it is being discussed. It’s far easier to jump on the most popular bandwagon – and sometimes having done so … remain ignorant of the facts … or worse, maybe influence some reasonably inexperienced aviator out there who gloms onto something posted by a seasoned old fart and finds out that he or she has made a serious error in judgment. There is absolutely no reason to NOT learn the truth about anything discussed here – because the truth will not only set you free, it might also save your butt!!
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Old 30th Sep 2013, 21:59
  #142 (permalink)  
 
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Quote:
Hey John – this forum, and by extension, YOU, do(es), and have done, what most here would describe as a magnificent job of reviewing the posts and allowing the development of what develops.
...You, sir, and this forum, deserve at least a handful of “atta-boys” for the kinds of information exchange you provide to all of us – and there’s probably no way to measure the value that has produced.

Hear, hear... Thanks for articulating those sentiments much better than I for one could have done, AirRabbit. Something as close to the truth as fallible humans can aspire to will out... eventually.
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Old 30th Sep 2013, 22:26
  #143 (permalink)  
 
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Originally Posted by AirRabbit View Post
You, sir, and this forum, deserve at least a handful of “atta-boys” for the kinds of information exchange you provide to all of us...
Perfectly put.

And on a more personal note, I should thank the mods for being lenient to an enthusiast with scant qualifications, who as a result has learned more than he ever could hope to have done any other way. Not to mention making the acquaintance of several stellar pilots, engineers and people in the process.
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Old 30th Sep 2013, 23:35
  #144 (permalink)  
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Guys .. enough, already ... lest I get an undeserved swelled head.

However, this forum is too important for the folks who use it to let it swing too far either way .. better we maintain a reasonably polite but vigorous and spirited debating platform for whatever topics arise.

We all have the potential to learn from PPRuNe.

I have a small insight into the IDs of some of the posters. If you or I were to seek their advice on a commercial consultancy basis (and many of them are highly regarded Industry Consultants), we would be paying a small fortune for what we are getting here as freebies.

That never ceases to amaze me.
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Old 1st Oct 2013, 01:06
  #145 (permalink)  
 
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Air - Their report will say the pilots shouldn't use too much rudder...but what isn't in the report is that Airbus has quietly inspected, fixed, and stiffened up all the tails.
Really? Airbus stiffened all the tails? On just the A300's? Or the A300-600R's? Is there a difference between the two aircraft? Does it matter?

Or did Airbus stiffen every Airbus tail ever built?
When did they do this? What was the 'fix'?
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Old 1st Oct 2013, 04:36
  #146 (permalink)  
 
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Hear, hear for and to those who quite rightly have applauded JT. A gentleman much experienced aviation wise, and does the greatest of jobs riding herd on this community of cats. Helo guy myself, know nought of big iron, but through these august pages have had the privalege of correspondance with proffesionals who have worked and flown on aircraft mere mortals can only dream about. All spilling errors tablet induced.
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Old 1st Oct 2013, 10:33
  #147 (permalink)  
 
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The NTSB Accident Report on AA 587, paragraph 1.18.10 Airbus Technical Note, states:
On April 8, 2004, Airbus issued a technical note, titled “AAL 587 – Pedals Force Analysis,” that provided Airbus’ estimate of the rudder pedal forces during the seconds before the vertical stabilizer separated from the airplane. Airbus used FDR data for rudder pedal position, estimates of rudder position, estimates of yaw damper position, and ground test data to derive the pedal force estimate.
The technical note indicated that, during the accident sequence, the forces applied by the first officer to the rudder pedals were much higher than the forces required to reach the rudder travel limit for 240 knots. Airbus found that the highest force applied by the pilot during the accident sequence was about 140 pounds but that the pedal force required to reach the rudder travel limit during that time was about 30 pounds. The note further indicated that the rudder control cable was stretched each time that the rudder travel limit was contacted.
The Airbus note is not discussed in the NTSB report that was published in october 2004, and I could not find it on the NTSB website. Has anyone more information?
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Old 1st Oct 2013, 13:24
  #148 (permalink)  
 
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Originally Posted by Air Rabbit #135
… remain ignorant of the facts …
Despite reading PPRuNe and our august posters, I am still ignorant of the exact text of FAA's Va old and new definitions Is it Defence secrecy?

@Clandestino
Originally Posted by roulishollandais
What we learned first, Critical situation
• Not sure you have taught new pilots. Did you ?
• We don't have the same definition of "critical [situation]"

Last edited by Jetdriver; 1st Oct 2013 at 15:16.
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Old 1st Oct 2013, 14:11
  #149 (permalink)  
 
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Quote from dutchroll:
Despite reading PPRuNe and our august posters, I am still ignorant of the exact text of FAA's Va old and new definitions.

You and me both!
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Old 1st Oct 2013, 14:34
  #150 (permalink)  
 
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@Chris, Roulis

I think you will find what you are looking for in posts #21 and 23 of the "Va Maneuvring" thread.

This involves subtle distinctions between "Maneuvring speed" and "Design Maneuvring speed". I suspect this was the origin of this thread, but Teldorserious hasn't confirmed that despite repeated requests.
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Old 1st Oct 2013, 15:14
  #151 (permalink)  
 
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Va is defined in FAR 25.335, last changed with Amdt. 25-91 Eff. 7/29/97. The change was made to harmonize FAR and JAR.
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Old 1st Oct 2013, 15:29
  #152 (permalink)  
 
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Va is defined in FAR 25.335, last changed with Amdt. 25-91 Eff. 7/29/97. The change was made to harmonize FAR and JAR.
Agreed HN, but that refers to the design manoeuvre speed. The FAA changes made following the NTSB AA587 recommendation related to FAR 25.1507 and 25.1583
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Old 1st Oct 2013, 15:51
  #153 (permalink)  
 
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Originally Posted by roulishollandais
Quote:
Originally Posted by Air Rabbit #135
… remain ignorant of the facts …
Despite reading PPRuNe and our august posters, I am still ignorant of the exact text of FAA's Va old and new definitions Is it Defence secrecy?
Umm … forgive me, but I’m not sure if you’re asking a question or not … and if you are, I’m not sure what that question might be. If you are seeking to read the FAA’s current definition of Va, here is a reference for you to read: § 25.335 Design airspeeds.
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Old 1st Oct 2013, 15:53
  #154 (permalink)  
 
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Originally Posted by Owain Glyndwr View Post
When AA587 lost its fin it also lost all hydraulics since it was supplied by all three systems. Consequently there was no aerodynamic control of any sort available...
While you're absolutely correct in a technical sense, if I understand it correctly the sequence of events following vertical stab separation progressed so quickly that there wouldn't have been enough time for the hydraulic fluid to drain.

I'm pretty sure that because the aircraft was already in a sideslip, the resultant loss of opposing force from the rudder/stabiliser would have caused what amounted to an unrecoverable flat spin within a fraction of a second, would it not?
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Old 1st Oct 2013, 16:24
  #155 (permalink)  
 
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@AirRabbit

If you go back to the OP you will find it querying
FAA changes to "Va"
after the Airbus deal
I take this to mean the changes FAA made to their regulations as a result of NTSB pointing out the confusion that existed between Va used as a design speed and Va used as a manoeuvre speed.

If you check out the posts I cited earlier you will find that the FAA made changes to the definition of the latter, not to Va used as a design speed. Consequently I think that referring RH and CS to the latest definition of manoeuvre design speed won't help them - hence my reference to an earlier PPRuNe discussion.

@ Dozy

Not so much time to drain the systems Dozy, just that if the pipes are open to the atmosphere the working pressure drops to zero, so the remaining control surfaces will flop all over the place under whatever aerodynamic hinge moments they might experience.

I don't think we know anything about the subsequent gyrations and I would certainly not like to attempt any prediction - they were nowhere near stall when if happened so I don't see why it should develop an almost instantaneous flat spin - in fact a aircraft that size will not do anything much in a fraction of a second.

Last edited by Owain Glyndwr; 1st Oct 2013 at 16:25.
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Old 1st Oct 2013, 16:26
  #156 (permalink)  
 
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Owain,

Thanks, I just couldn't find the thread you referred to.
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Old 1st Oct 2013, 16:45
  #157 (permalink)  
 
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Originally Posted by Owain Glyndwr View Post
I don't think we know anything about the subsequent gyrations and I would certainly not like to attempt any prediction - they were nowhere near stall when if happened so I don't see why it should develop an almost instantaneous flat spin - in fact a aircraft that size will not do anything much in a fraction of a second.
Fair enough - I was speculating on possible momentum build-up from those pendulum-like yaw movements, but admittedly I'm way out of my depth - so if you say it's unlikely then I'm with you!
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Old 1st Oct 2013, 20:14
  #158 (permalink)  
 
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Originally Posted by Owain Glyndwr
@AirRabbit

If you go back to the OP you will find it querying
Quote:
FAA changes to "Va"
Quote:
after the Airbus deal
I take this to mean the changes FAA made to their regulations as a result of NTSB pointing out the confusion that existed between Va used as a design speed and Va used as a manoeuvre speed.

If you check out the posts I cited earlier you will find that the FAA made changes to the definition of the latter, not to Va used as a design speed. Consequently I think that referring RH and CS to the latest definition of manoeuvre design speed won't help them - hence my reference to an earlier PPRuNe discussion.
Thanks … and I have gone back to the thread and the posts you referenced – and interestingly in my dim memory, I vaguely recall the discussions that took place in my circle of colleagues when all that occurred … and even with those discussions I don’t think that any of us had that proverbial “light bulb” experience – because even with deciphering each individual word – there were still some areas that, at least to most of us, seemed contradictory or at least argumentative.

However, after all that, even with whatever level of understanding any of us may have had (even full understanding) with respect to what the revised regulation would have required or allowed, there is still the issue of not only control reversals, but multiple reversals, most of which were to the control limits, that would throw out all of the attempts to understand any logic or generate any sympathy for any such lack of intelligent understanding of those re-written rules. I still come back to not understanding why that pilot chose such wholly different control applications for what was essentially the same encounter twice.
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Old 1st Oct 2013, 20:52
  #159 (permalink)  
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Re Regulations and, hence, in this case, what Va might have meant from time to time ...

FAA current and superseded regs can be tracked down from here.

Always one has to keep in mind that the regs should not be read in isolation but in conjunction with relevant ACs.

Tracking down superseded ACs can be a bit of a pain, unfortunately.
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Old 1st Oct 2013, 23:25
  #160 (permalink)  
 
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Va definitions

@john_tullamarine, Owain Glyndwr, AirRabbit, Hazelnuts39, OK465, others...
Thank you very much to all : a big step has been done . I have much to read now before continuing to try to compare two definitions of Va. Strange but useful thread starting with a not so easy question as it seems. THANKS AGAIN!

Edit : add Short extract :
Code of Federal Regulations

Sec. 25.335

Part 25 AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES Subpart C--Structure Flight Maneuver and Gust Conditions

Sec. 25.335

Design airspeeds.

The selected design airspeeds are equivalent airspeeds (EAS). Estimated values of and must be conservative. (a) Design cruising speed, V C . For V C ,the following apply: (1) The minimum value of V C must be sufficiently greater than V B to provide for inadvertent speed increases likely to occur as a result of severe atmospheric turbulence. [(2) Except as provided in Sec. 25.335(d)(2), V C may not be less than V B + 1.32 U REF (with U REF as specified in Sec. 25.341(a)(5)(i)). However V C need not exceed the maximum speed in level flight at maximum continuous power for the corresponding altitude.] (3) At altitudes where V D is limited by Mach number, V C may be limited to a selected Mach number. (b) Design dive speed, V D . V D must be selected so that V C / M C is not greater than 0.8 V D / M D ,or so that the minimum speed margin between V C / M C and V D / M D is the greater of the following values: (1) From an initial condition of stabilized flight at V C / M C ,the airplane is upset,flown for 20 seconds along a flight path 7.5° below the initial path, and then pulled up at a load factor of 1.5g (0.5g acceleration increment). The speed increase occurring in this maneuver may be calculated if reliable or conservative aerodynamic data is issued. Power as specified in Sec. 25.174(b)(1)(iv) is assumed until the pullup is initiated, at which time power reduction and the use of pilot controlled drag devices may be assumed. [(2) The minimum speed margin must be enough to provide for atmospheric variations (such as horizontal gusts, and penetration of jet streams and cold fronts) and for instrument errors and airframe production variations. These factors may be considered on a probability basis. The margin at altitude where M C is limited by compressibility effects must not be less than 0.07M unless a lower margin is determined using a rational analysis that includes the effects of any automatic systems. In any case, the margin may not be reduced to less than 0.05M.] (c) Design maneuvering speed, V A . For V A ,the following apply:

(1) V A may not be less than where--(i) n is the limit positive maneuvering load factor at V C ; and (ii) is the stalling speed with flaps retracted. (2) V A and V S must be evaluated at the design weight and altitude under consideration. (3) V A need not be more than V C or the speed at which the positive C Nmax curve intersects the positive maneuver load factor line, whichever is less. (d) Design speed for maximum gust intensity, V B . (1)

Vb ≥Vs1 [ 1 + Kg. Uref. Vc. a / 498 w ] ^ ½

where--V S1 = the 1-g stalling speed based on C NAmax with the flaps retracted at the particular weight under consideration; V C = design cruise speed (knots equivalent airspeed); U REF = the reference gust velocity (feet per second equivalent airspeed) from Sec. 25.341(a)(5)(i); w = average wing loading (pounds per square foot) at the particular weight under consideration.

Kg = .88 Mu / 5.3 + Mu
Mu = 2w / r.c.a.g

r = density of air (slugs/ft ); c = mean geometric chord of the wing (feet); g = acceleration due to gravity (ft/sec ); a = slope of the airplane normal force coefficient curve, C NA per radian; (2) At altitudes where V C is limited by Mach number--(i) V B may be chosen to provide an optimum margin between low and high speed buffet boundaries; and (ii) V B need not be greater than V C . (e) Design flap speeds, V F .. For V F ,the following apply: (1) The design flap speed for each flap position (established in accordance with Sec. 25.697(a)) must be sufficiently greater than the operating speed recommended for the corresponding stage of flight (including balked landings) to allow for probable variations in control of airspeed and for transition from one flap position to another. (2) If an automatic flap positioning or load limiting device is used, the speeds and corresponding flap positions programmed or allowed by the device may be used. (3) V F may not be less than--(i) 1.6 ,with the flaps in takeoff position at maximum takeoff weight; (ii) 1.8 ,with the flaps in approach position at maximum landing weight; and (iii) 1.8 with the flaps in landing position at maximum landing weight. (f) Design drag device speeds, V DD . The selected design speed for each drag device must be sufficiently greater than the speed recommended for the operation of the device to allow for probable variations in speed control. For drag devices intended for use in high speed descents, V DD may not be less than V D . When an automatic drag device positioning or load limiting means is used, the speeds and corresponding drag device positions programmed or allowed by the automatic means must be used for design.

Amdt. 25-91, Eff. 7/29/97

Last edited by roulishollandais; 1st Oct 2013 at 23:48. Reason: add short extract
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