He stepped on the Rudder and redefined Va

[HazelNuts39]

Originally Posted by Pugilistic

An accelerated stall above Vp would impart a force that is above the limit load

Is that true? As a layman I would think that although the load factor at Va may exceed nlimit, the load would not exceed limit load. But then I don't know much about structures.

[Clandestino]

Originally Posted by bubbers44

If our A300 going out of control with yaw damper movements at 140 knots into MIA had happened at 250 knots would the VS had departed?

Is this what you are referring to?

Originally Posted by Aviaton safety network narrative of AA903, May 12 1997

The flight was assigned an airspeed of 230 knots and cleared to descend from FL240 to 16,000 feet in preparation for landing at Miami. The FDR indicated that while the autopilot was engaged in the descent, the power levers moved from the mechanical autothrottle limit of 44 degrees to the manual limit of 37 degrees. As the aircraft leveled at 16,000 feet the airspeed decreased. The F/O began a right turn to enter a holding pattern and added some power, which stabilized the airspeed at 178 knots. However, the right bank and the resultant angle of attack (AOA) continued to increase, despite left aileron input by the autopilot. As the autopilot reached the maximum input of 20 degrees, bank angle increased past 50 degrees, and the AOA increased rapidly from 7 degrees to 12 degrees. At this point the stick shaker activated, the autopilot independently disconnected, the power was increased, and full left rudder was used to arrest the roll. The bank angle reached 56 degrees, and the AOA reached 13.7 degrees at 177 knots. The aircraft then pitched down, and entered a series of pitch, yaw, and roll maneuvers as the flight controls went through a period of oscillations for about 34 seconds. The maneuvers finally dampened and the crew recovered at approximately 13,000 feet. One passenger was seriously injured and one flight attendant received minor injuries during the upset.
An analysis showed that the forces during the upset not only had gone above the design limit of the vertical stabilizer, they also apparently had reached the ultimate limit. In June 1997, Airbus requested that American Airlines perform another inspection of the jet to ensure it was not damaged. American inspectors, following Airbus' instructions, examined the tail fin. But they did not use methods that would have allowed them to see inside the tail fin. They saw no damage from their visual inspection, and the jet continued to fly until an ultrasound inspection of the horizontal stabilizer was done in March 2002. The inspection found two crescent-shaped cracks at one of the points where the tail fin attaches to the fuselage. The fin was replaced.

PROBABLE CAUSE:"The flightcrew's failure to maintain adequate airspeed during leveloff which led to an inadvertent stall, and their subsequent failure to use proper stall recovery techniques. A factor contributing to the accident was the flightcrew's failure to properly use the autothrottle."

Originally Posted by Bubbers44

Yes, I know the rudder deflections on FDR but as I said recently my friend had uncomanded out of control deflections and they were not touching the rudders in their A300.

Is 1997. recent or there was another incident recently that no one around seems to know about?

[bubbers44]

I remember that one too but this one about 20 years ago was on final approach to MIA requiring a go around because of uncommanded rudder movements that they could not stop. I would guess the NTSB would have blamed the pilots if they had crashed as they both thought was going to happen. I will try to find the report and post it.

[bubbers44]

A300 rudder actuator

An airbus 300 on final approach at 1000 ft experienced uncommanded rudder inputs and rudder pedals v... - NASA ASRS

[Owain Glyndwr]

HN39

As a layman I would think that although the load factor at Va may exceed nlimit, the load would not exceed limit load.

The limit load (assuming the aircraft is designed by manoeuvre loads not by gust loads) would be 2.5g at MTOW and fwd CG limit. Strictly speaking that should be at MTOW less whatever fuel you burn to get there, but WTH! At Va you can just pull 2.5g at whatever weight has been used to define Va.

So if you are at a weight close to MTOW and at a speed above Va for that weight then you could in principle exceed both the 2.5g limit and the limit load. But at those conditions it is unlikely that one could pull enough 'g' to get anywhere near ultimate load (3.75g @ MTOW) if only because to get to a weight/airspeed condition where one could pull 3.75g one would have to burn off enough fuel to reduce the weight well below MTOW.

[Owain Glyndwr]

bubbers44

Thank you for posting that report, but since it says several times that re-engaging the yaw dampers made things slightly easier, and since the problem was diagnosed as a failed autopilot yaw actuator clutch I don't see how your position re yaw damper failure as a possible cause of AA587 rudder movements can be sustained. Comment?

[SMOC]

If the FCC detects a disagreement between the autopilot clutch and the autopilot selection, the FCC will command the respective main valve solenoid to close, thus depressurizing that channel of the autopilot actuator.

The examinations revealed two main findings: (1) the wiring to the two main valve solenoids had been cross-connected, and (2) a foreign-particle contaminant was found in the green system engagement valve solenoid.

Examination of the actuator at the Lucas facility revealed that its two main valve solenoids were cross-connected so that the electrical connection for the yellow system was connected to the green system solenoid, and vice versa. In this configuration, the FCC for the green system would actually control the main valve for the yellow system, and the FCC for the yellow system would control the main valve for the green system.

After the cross-connected wiring on N7082A was discovered, Airbus issued an All Operators Telex (AOT) on May 27, 1999, to all operators of Airbus A300, A310, and A300-600 airplanes. The AOT specified that a one-time inspection be conducted within 10 days to confirm proper connection of the main valve solenoids.

As a result of the AOT checks, another American A300-600 (N3075A) autopilot yaw actuator (S/N 1630) was discovered with cross-connected autopilot solenoid wiring. American indicated that it had installed new solenoids on the three actuators (pitch, roll, and yaw) on this airplane and the rest of its A300 fleet between July 1997 and July 1999. At the time the new solenoids were installed, procedures did not specifically include a check to ensure that the solenoid wiring was installed properly. Both Airbus and Lucas have since developed new procedures to ensure that the autopilot actuator solenoids are properly wired.

Lucas Aerospace, which is now known as TRW Aeronautical Systems obviously builds parts for Boeing and others as well.

And as stated above nothing to do with yaw dampers.

[HazelNuts39]

Thanks Owain,

I probably misunderstood PA's remark.

[bubbers44]

As I said I was using the info the FO gave me after the incident. I didn't read this report until a couple of hours ago. I agree they found rudder actuator clutch problems. I am curious how that would cause uncommanded rudder deflections. Seems like the rudder would either work or not work.

[AirRabbit]

Originally Posted by flarepilot

by the way puglist

one plane I flew says don't move control wheel more than half way above FL400

now certainly I know that, but there is a placard...

I wonder, with the placard reading “don’t move the control wheel more than half-way above FL400” … I would presume that you would feel perfectly comfortable in moving the control wheel to ˝ of it’s maximum throw (I would presume that would be somewhere in the neighborhood of 67 degrees either side of neutral, right?) even if you were operating at FL410. Since you’re comfortable in moving the control wheel this way, how about moving it to 67 degrees left, and then immediately moving it to 67 degrees right, and then back to 67 degrees left, and then back to 67 degrees right, and keep that up for some 6 to 8 repetitions. Please note, the control wheel would not be moved more than half-way, so there would be no problem … right?

And, since there is apparently no placcard saying anything about a similar use of the rudder - would you consder doing the same control deflections - this time to the "stop" (physical or rudder limiter) for that same 6 or 7 repetitions. No placcard ... so ... no problem? Maybe, taking a clue from the lateral control placard, you might consider limiting your rudder inputs and reversals to only the same ˝ value?

[AirRabbit]

Originally Posted by john_tullamarine

It is well understood by the engineering pilots around that there is a great problem with pilot education when it comes to what the certification animal does as contrasted with the line flight standards animal.

Fact of life and it is going to be a long while, if ever, before the typical pilot's knowledge base is lifted to the point where he/she has a basic idea of certification stuff.

.. which is why this Forum is so important. We have a bunch of very well credentialled

(a) line, training, check pilots

(b) TPs and FTEs

(c) certification, design, test engineers, aerodynamicists etc

(d) many anciliary specialists in airports and a host of other disciplines

The problem is that, sometimes, it can be difficult to sort the wheat from the chaff when posters are anonymous but that's a small problem overall as the more experienced folks offer comments (not always as subtle as might be desirable) which provide clues ...

Well, said – and, of course, quite accurate. And, in that same vein, with perhaps more than a little naiveté on my part, it would be my hope that ALL the readers here would take everything posted here as a potential fact until researched or thought through - or determined to be a perspective from a preconceived and/or prejudicial position and not necessarily willing to have the facts or truth lead to the ultimately correct conclusion. As for me personally, I choose to remain anonymous. The only reason for this decision, as I’ve said previously, is that I don’t think my employer would be appreciative of my “sounding off” (as you know I do) in such a public forum. I have a reputation with my employer for doing the same thing on the job and I pay for it regularly … but what I say is almost always retained within the organization in which I toil, and at least I still have my job - and I hope to keep it. However, if I were the janitor at the local Trailways Station – I can suspect what my “believability” might be … and, conversely, if I were the Senior Advisor to the FAA Administrator or the NTSB Deputy Chairman, whatever I say might (just might) enjoy some undeserved acceptance with little or no scrutiny. So, I prefer to offer what I offer in the hopes that I’ve made my points clearly and honestly enough to not depend on such “positional authority” to have anyone who reads what I say understand the accuracy of my comments.

[bubbers44]

Unless you are doing 8pt hesitation rolls rarely do you need much more than 20 percent control movement in any aircraft.

[AirRabbit]

Originally Posted by Pugilistic Animus

…how did the plane fail them when they were doing a maneuver outside of certification? I think their training in wake encounter recovery failed them i feel bad for the flight crew and I don't really blame them as the copilot was simply doing what he was taught ...

With all due respect, sincerely meant, I’m not at all sure that the Wake Turbulence training they received was insufficient or even wrong. Recall that the tail was twisted off the airplane due to the F/O’s indiscriminate use of rapid rudder and wheel control inputs to the stops and just as rapid reversals of both controllers on repeated occasions … BUT … that was the SECOND vortex encounter. The FIRST encounter was transitioned without incident – by the same F/O, doing exactly what he had been trained to do – essentially rely on the inherent stability of transport category airplanes, aided ever so slightly by very minor control wheel inputs to aid or hasten return to wings-level. In fact the rudder controls were barely moved and the rudder surface was barely displaced.

[AirRabbit]

I guess we'll never know why this F/O did what he did the SECOND time he encountered a wing tip vortex on the SAME departure ... 5 or 6 seconds after the first encounter recovery ... but it certainly wasn't what he was trained to do.....

[bubbers44]

I guess he forgot everything he did a few seconds before and since that worked so well decided to stomp on the rudders until the tail fell off on the second encounter. Then again did anybody check the rudder actuator clutch? If it happened once it could happen again. I wonder if it was the same airplane?

[bubbers44]

The upset training we got we all knew was to use the rudder in low speed upsets on approach to maximize recovery not for 250 knot speeds. It had nothing to do with AA Airbus crash in my opinion.

[AirRabbit]

Originally Posted by bubbers44

Then again did anybody check the rudder actuator clutch? If it happened once it could happen again. I wonder if it was the same airplane?

On the surface that might look like an excellent question. But, I think the report indicates that when this particular error manifested itself on the approach into Miami (I think) the airplane was apparently found to have had maintenance cross-connecting the autopilot servos (wasn’t it) and they said that it was extremely difficult to move the rudder pedals. The rudder pedals on AA587 were apparently quite easily moved … as the F/O move them from stop to stop some 5 times in 7 seconds. That doesn’t sound like “very difficult to move.”

[bubbers44]

So you think FDR rudder inputs are measured at the pedals, not at the rudders?
I would like to see what the FDR showed on the MIA Incident when they couldn't move the rudder pedals but the rudder was out of control yawing the aircraft.

[roulishollandais]

Miami Dutch roll • Oct 4, 2013 1:47:44 AM
I say it again AA587 was steady in the turbulent airflow before the unappropriate sharing actions on pedals. Miami is confirmed to have started as a dutch roll due to yaw A/P failure.

A real dutch roll is an OSCILLATION from one side to another with increasing bank due to resonance.

Despite you have a yaw movement in the dutch roll, the names says it well it s a ROLL oscillation, to be corrected with the stick not with pedals.

Don't confuse dutch roll with a low prestall flight that you control with rudder. A stall probably will evoluate to a spin on one side not with that bank oscillation from one side to the other.

Spiral is another situation with bank on a single side.

Lazy eight is already a little different : the dynamic oscillation is present but stays on the step of resonance. The flight remains not really unstable.

In the dutch roll the pilot has a very active role when he flies as learned.

Controling a dutch roll gets really scabrous if you feed his closed loop with energy: and we know that reserves of energy are unlimited so long te plane is not on the ground and stopped (potential and kinetic energy). If you "play" a little more with oscillations or configration or thrust, you continuesly tansfer energy bags... that is very bad! If you know nothing about dutch roll, but have identified it, and have some room under you, the best is to put feet on the ground and hand on the knees : not very easy for a pilot in emergency!! If you are near of the ground, first go around, get altitude...
I suppose you had already applied oscillation abnormal procedure (yaw damper off/alt probably).

Using only the half, or 20%, of the control is not sufisant to overcome quickly a dutch roll. You have to use controls as some exact moment and at exact speed, after you leaved an exact number of seconds action on controls.

The dutch roll closed loop may be controled if you do not pull your plane in furious dynamic. Help the plane to find back quietly his first (!!) order natural oscillation (stopping to shake it!) , don't try to compute in your head when piloting an emergency a second, third, fourth degree system you builded yourself by that shaking : it is just impossible.

Let us jump here equations which don't figure in the well known n/speed stall and gusts enveloppe. But sailors know something looking like dytch roll, the French name is "roulis rythmique". Another similar dynamic is that of the toreador : banderillas are used to oblige the animal to use only first degre movement.

The dynamic of the dutch roll affects not only the position and attitude and bank of the dutch rolled pkane, but also the airflow around the plane, resulting in the very strong effect catching the plane as in a net and doing very difficult some movements. Miami report shows that phenomena which has to do with our bad knowledge of ..theory of lift.

Originally Posted by roulishollandais 26.sept2013 this thread #27

We have two very different situations :

- The flightAA587 wastooken in a heavyand quick wake turbulence and the first officer did that violent pedal sharing very quickly - probably the captain had feet on the ground and could not avoid his FO pedaling quickly enough. It is a non pilot induced big oscillation of the airflow where the A300-600 had a stable dynamic, followed by a pilot action near of shocks givingexcessive conventional aerodynamic forces.

- In the both cases with Yaw damper failure, the possibility of DUTCH ROLL is important. You avoided it on your B727. Your friend and his Captain had less chance and developped the dutch rolll which is a resonance between the airflow movement around the whole aicraft and action with roll and/or rudder of the pilot to stop that PIO -inadequatlybecausethedutch rollisnot taughtto pilotsnoredescribed in ATPL books, where the problem is described as non existing with the yaw damper . But dutch roll may start by other initial disturbation - pushing one pedal violently (..in a sim issafer ) - and the pilot feeds himself the resonance acting on the stick and pedals AT THE WRONGMOMENT ANDWITH INADEQUATE SPEEDS. A good aerobaticflightculture may avoid/correct that resonance without equation, but it may be solved, in flight, by equations too.

[bubbers44]

AA587 wasn't a dutch roll. It started with wake turbulence and ended up with rudder movement causing the VS to fail. The question is was it pilot induced or did the airplane do it. I believe the airplane did it. Our MIA incident at their speed if repeated could be why it happened. I think the FDR actually measures the rudder movement, not pedal movement so would like to see the read out of the MIA incident vs JFK crash and compare them. MIA, the pilots couldn't move the rudder pedals but JFK it shows full deflection. Did anybody ever bother to compare them? Probably not. If I was in the NTSB I would because the FO is being blamed for what the rudders did but I don't think he pushed the rudders, the A300 systems did again. I could be wrong but I don't think so.