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.

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FAA current and superseded regs can be tracked down from here.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Tracking down superseded ACs can be a bit of a pain, unfortunately.

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

Well I am not buying it that airliners are so weak that some pilot or terrorist could intentionaly wiggle the tail loose. If that is the case, something is wrong with the hydros or the tail or the sensors or limiters that allow such actions.

Maybe the solution is to take the hydros out of it, make it all cranks and levers. If the pilot wants to put some rudder in, make him work for it, fight those aerodynamic forces, just like the rest of us in smaller planes that can't even imagine having enough legs to knock a tail off.

How about calling Boeing and Airbus and explaining YOUR theory to them? They disagree. Whip out your crayons and show them where they're wrong.

If anyone else is hearing a faint buzzing noise, like an angry wasp banging against a window - I'd recommend ignoring it.

Misd - No one except a few peeps on PPRUNE believe that wiggling the tail will crash a plane, any more then three pilots over the Atlantic can't fly straight and level.

misd-again

Didn't you mean finger paints?

With respect to superseded ACs.

Online Digital Special Collections Library

This site appears to have many and is apparently not affected by the US government shutdown. It was not easy to find, however.

Teldorserious,

Pedal forces of up to 140 lbs ... Just wiggling the tail, eh?

Thanks JT for the link to historical aviation requirements.

On December 31, the requirement that specifies the design tail loads in the yaw maneuver (currently FAR 25.351, formerly CAR Part 04 section 4b.215) will celebrate its 60th birthday!

.. and thank you to David Bass from us all for his gem.

Oh, the love.

And Boeing, and Airbus, and the NTSB, and the FAA.

But in the internet world? Yup, it's a fraud. Good catch by you.

Now which a/c models did Airbus 'fix' the tails on? How? When?

I'm just waiting for some one to realise that wiggling the stick to and fro above a certain speed makes the wings fall off. Wonder what his solution may be?

Just a thought...

Maybe what we should do is ask Teldor(no-one-really-believes-she-is)serious to take a Cessna 152 out for a trip around the traffic pattern and, on the downwind leg, do what was done on the 2nd vortex encounter on AA587. Is there anyone here who believes she will do it?

I don't think even that's necessary. One way to think about it is that following Delta191 at DFW, the NTSB commissioned a study that involved deliberately driving a 737 through microbursts in order to collect data - a risky prospect. After Roselawn, they flew an ATR-72 behind a tanker spraying chilled water over the wings to study the ice ridge build-up behind the de-icing boots - an incredibly risky prospect.

And yet they never even entertained the idea of going up in an A300 or B767 and repeating the rudder pedal movements they saw on the AA587 FDR. That should speak volumes to a dispassionate observer.

Actually, I heard that they actually did discuss doing just that, but when the proposal was made in front of an audience of all the Airbus and Boeing test pilots, all five of the pilots who volunteered (all the rest scrambled out of the auditorium quickly) agreed only to man the ground based photo record cameras.

NTSB Press Release
National Transportation Safety Board
Office of Public Affairs
________________________________________
NTSB SAYS PILOT'S EXCESSIVE RUDDER PEDAL INPUTS LED TO CRASH OF AMERICAN FLIGHT 587; AIRBUS RUDDER SYSTEM DESIGN & ELEMENTS OF AIRLINE'S PILOT TRAINING PROGRAM CONTRIBUTED

OCTOBER 26, 2004

Washington, D.C. - American Airlines flight 587 crashed into a Queens neighborhood because the plane's vertical stabilizer separated in flight as a result of aerodynamic loads that were created by the first officer's unnecessary and excessive rudder pedal inputs after the aircraft encountered wake turbulence, according to a final report adopted by the National Transportation Safety Board today. The Board said that contributing to the crash were characteristics of the airplane's rudder system design and elements of the airline's pilot training program.

At about 9:16 a.m. on November 12, 2001, flight 587, an Airbus A300-605R (N14053), crashed in Belle Harbor, New York shortly after taking off from John F. Kennedy International Airport on a flight to Santo Domingo. All 260 people aboard the plane died, as did five persons on the ground. This is the second deadliest aviation accident in American history.

The aircraft's vertical stabilizer and rudder were found in Jamaica Bay, about a mile from the main wreckage site. The engines, which also separated from the aircraft seconds before ground impact, were found several blocks from the wreckage site. The Safety Board found that the first officer, who was the flying pilot, inappropriately manipulated the rudder back and forth several times after the airplane encountered the wake vortex of a preceding Boeing 747 for the second time. The aerodynamic loads placed on the vertical stabilizer due to the sideslip that resulted from the rudder movements were beyond the ultimate design strength of the vertical stabilizer. (Simply stated, sideslip is a measure of the "sideways" motion of the airplane through the air.)

The Board found that the composite material used in constructing the vertical stabilizer was not a factor in the accident because the tail failed well beyond its certificated and design limits.

The Safety Board said that, although other pilots provided generally positive comments about the first officer's abilities, two pilots noted incidents that showed that he had a tendency to overreact to wake turbulence encounters. His use of the rudder was not an appropriate response to the turbulence, which in itself provided no danger to the stability of the aircraft, the Board found.

The Board said that American Airlines' Advanced Aircraft Maneuvering Program contributed to the accident by providing an unrealistic and exaggerated view of the effects of wake turbulence on heavy transport-category aircraft. In addition, the Board found that because of its high sensitivity, the A300-600 rudder control system is susceptible to potentially hazardous rudder pedal inputs at higher speeds. In particular, the Board concluded that, before the crash of flight 587, pilots were not being adequately trained on what effect rudder pedal inputs have on the A300- 600 at high airspeeds, and how the airplane's rudder travel limiter system operates.

The Safety Board's airplane performance study showed that the high loads that eventually overstressed the vertical stabilizer were solely the result of the pilot's rudder pedal inputs and were not associated with the wake turbulence. In fact, had the first officer stopped making inputs at any time before the vertical stabilizer failed, the natural stability of the aircraft would have returned the sideslip angle to near 0 degrees, and the accident would not have happened. (The Board estimated that the sideslip angle at the time the vertical stabilizer separated was between 10 and 12.5 degrees.)

The NTSB issued eight recommendations in today's report. Among the seven sent to the Federal Aviation Administration were those calling for adopting certification standards for rudder pedal sensitivity, modifying the A300- 600 and A310 rudder control systems to increase protection from potentially hazardous rudder pedal inputs at high speeds (a similar recommendation was issued to the French equivalent of the FAA, the DGAC), and publishing guidance for airline pilot training programs to avoid the kind of negative training found in American Airlines' upset recovery training.

Because this crash occurred two months after the September 11 terrorist attacks, there was initial concern that it might have been the result of an intentional criminal act. The Board found no such evidence, nor did any law enforcement agencies provide evidence that the accident may have stemmed from criminal conduct. The Board said that witnesses who reported observing the airplane on fire were most likely observing misting fuel released from broken fuel lines, a fire from the initial release of fuel or the effects of engine compressor surges.

A summary of the Board's report may be found under "Publications" on the agency's website at NTSB - National Transportation Safety Board. The full report will appear on the website in about four weeks.

NTSB Office of Public Affairs: (202) 314-6100

the NTSB is full of humans...humans make mistakes...we have our opinions based on years of whatever we have been doing

my opinion is the airbus 300 series is a piece of shirt

remember that the FAA certified the A300

it also certified the training program used by American Airlines

it also certified the copilot


if they made a mistake somewhere, they could have made a mistake anywhere.

some engineering types are so concerned with elegance in engineering that they forget real life