He stepped on the Rudder and redefined Va

[AirRabbit]

It may be appropriate to offer just a tad more information on this specific issue… Not a lecture ... more of a plea ...

I think it quite valuable to understand the factors involved in the loads experienced on the vertical stabilizer / rudder under conditions when an airplane is “yawed” into a sideslip. A sudden rudder deflection will start a yaw, and, if the deflection is at maximum, you get the maximum rudder load. With this condition, the yaw will move the airplane tail to what is called an “over-swing” position. Once getting to that position, the airplane will experience the maximum torsion on the vertical tail. With the rudder in that position, the maximum force on the vertical stabilizer and the maximum force on the rudder surface are opposite each other. With the rudder held in this maximum deflected position, the airplane will oscillate from its “over-swing” position, and dampen down to a position known as “equilibrium yaw.” The same analysis is performed for engine failure, for rolling moments, and lateral (side-to-side) gusts. The most severe of these cases provides the design basis for the vertical stab and the rudder and is called the “limit load.” Here is where the 1.5 factor comes into play. The “ultimate load” is described as the “limit load” multiplied by 1.5. The structure must be able to support the “limit load” without permanent deformation that is detrimental to flight AND support the “ultimate load” without failure. The time for this test is 3 seconds. If either failure occurs within that 3 seconds, the test is failed. But (and it’s a VERY BIG “but”) when the airplane is in this maximum equilibrium yaw, a sudden commanded full, or nearly full, opposite rudder movement against that sideslip can generate loads that exceed the “limit loads” and possibly the “ultimate loads” and can result in structural failure. Certification limits do not consider the survivability of the structure under these extreme conditions.

I think that it is also important to understand that in order to begin to move any of the flight controls, there is what is known as a “break-out” force, or the force necessary to begin the controller movement - like the control wheel or rudder pedal. Once movement is started, there is a force necessary to continue to move the controller. But here we’re focused on the relevant control and control force is that necessary to move the rudder pedals. As you would probably suspect, the A300-600 rudder is hydraulically actuated – no surprise. In systems such as this, there is 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 an artificial “feel.” By way of comparison, a B767 (a similar sized airplane) at 250 knots has a breakout force of 17 pounds-feet (technical term) and the pilot would need to generate 80 pounds-feet to achieve maximum displacement – which in this airplane, is a bit over 3 and a half inches of rudder pedal travel and 8 degrees of rudder surface deflection. The A300-600 is noticeably different. 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). I don’t want to bore you with math, but the answer is that the A300 is over 7 times as sensitive as the B767; important enough to repeat … over 7 times as sensitive!! If you say this 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 A300 as in the B767.

I said that the AA587 F/O was at the controls and therefore must bear at least some of the responsibility. I stand by that statement. However, I should also acknowledge that, in my opinion at least, pilots are not often enough trained on the FULL aerodynamic envelope, and how to manage that envelope, of the airplane they fly. My background and experience is heavily focused on education and training – and, no, I don’t believe that education is the fix-all remedy. However, education AND training, in combination with experience, is the basis on which being a pilot should stand. And like anything else, the content of that education, training, and experience has to be appropriate for what the person (here, the pilot) will be expected to face and handle professionally and completely.

I think that this F/O was probably one of those individuals who took a lot of pride in his airmanship – and I suspect he probably was a very good pilot. I think he was the type of person who constantly wanted to correct back to what he was trying to hold - and don’t we all, at least to some degree? I also think that he probably was a bit unsure of the proper way to deal with a wing-tip vortex encounter. I think he was not advised of, and very probably not trained on, the problems that can develop with maximum control input and repeated maximum control reversals. I think he was not aware of the sensitivity of the controls, particularly of the rudder, and how much rudder he was getting with very little force applied and how little pedal deflection generated full surface deflection.

I am also aware that the organizations that hire pilots are not interested in having their pilots spending their “on duty” time 90% in training and 10% on the line. But the question quickly becomes, do we train pilots for the minimum regulatory requirements (which all – or most anyway – airlines do today) and depend on the “good-naturedness” of the management to volunteer additional time in training … or do we increase the mandatory training requirements to an appropriate level – and what IS that appropriate level? I believe this is an important question – not just to be hashed around at the local bar at overnight stops. Serious, committed effort is necessary to determine what is required – absolutely required – and what is “nice to know” kinds of things. This is NOT an easily defined goal – but I know that as long as we continue to ignore it … we’ll never get to the answer!