Hi
theamrad
(T)here's doubt in my mind about pilot perceptions. If I had only read the report and nothing else - I would probably sway more in favour of the second event being nothing unusual. However, I think ALL the evidence given in relation to metrology/wake turbulence effects during the public hearings warrants ,IMO, a bit more balanced/careful consideration than, for example, the casual inclusion of the statement "nothing extraordinary" by the main author of the wake vortex report in the board's final report. Doubt is raised in my mind about the POTENTIAL for something beyond the bounds of the "average" wake encounter in consideration of ALL the evidence which was available to me, and not just the final reports limited (very IMO) summary of the wake vortex data.
Of course, as we agree (I think) there is always going to be room for
some doubt. The question then becomes whether or not a particular thing is “likely” or “not likely;” or, is the doubt beyond reasonable?
From that, I think the question is relatively straight forward: Did the second wake turbulence encounter contain something that the first one did not? The preceding airplane did not change, except for the possibility of flap retraction (if the JAL crew delayed that long) – which, as I know you recognize, would only decrease the severity of any vortex generated. As far as we know there are no atmospheric condition(s) that could magnify the effect of an existing vortex.
According to the FDR a comparison of the aircraft responses to the first and second encounters compare as follows:
Variation in Longitudinal load factor:
First encounter 0.04 G drop Second encounter 0.07 G drop
Variation in Lateral load factor:
First encounter 0.07 G shift left Second encounter 0.05 G shift left
Variation in Vertical load factor:
First encounter 0.03 G drop Second encounter 0.04 G drop
With the amount of experience humans have in discerning a one-hundreth or a two-hundreth of a “G” difference, I would say that anyone would have concluded that these two encounters were, at the most, very, very similar.
But, as I've tried to indicate, they were in a sim which demonstrated, to a reasonable approximation, half the pedal sensitivity that the real aircraft does (section 1.17.1.2.7). Therefore, they had a better chance of getting the amount of rudder they wanted and not ending up in an APC event. On that one statement - I think the benefit of doubt should have been placed with the PF.
Granted, there may have been a difference in the “sensitivity” of the rudder pedal “feel” between the airplane and the simulator. That is primarily due to the fact that the airplane uses tension regulators and cables where the simulator uses software control of direct hydraulic pressure or electric motors to manage control “feel and application.” However, with the simulator being more sensitive, my experience is that this makes it more difficult, not less so, to get the amount of rudder desired. Additionally, if you carefully note the graph (Figure 18) depicted on page 91 of the report, you can see that the representative curves for the airplane and simulator rudder position/sensitivity are considerably different at the higher airspeed for application of “normal rudder pedal force.” However, when “high rudder pedal force” is used, the trace of the aircraft results very closely compares to that of the simulator.
We already know that most of the board's testers used some rudder when confronted with an upset - and by extension - I believe most line pilots would react in the same way. As for the PF here; Again this comes down to whether he thought he was in, or entering an upset or not. Was he? Almost without doubt/obviously - no. Did he think or perceive he was heading for one? Possibly. Why do I think that? Because, if the second encounter was just the same as the first, and it really was "nothing extraordinary", and he didn't perceive anything unusual - why on earth did he go for rudder in the second - and not the first? When pilots experience wake turbulence every day of the year to some degree or other, when so many consider that it's 'nothing unusual', and if the second event was no different from any other wake encounter - how could the PF in this case of lasted for over 1,800 hours on type?
Two things here: first, you have to recall that the “upset” recovery in the simulator had the simulator controls effectively rendered useless for the first part of the roll – that means that any pilot response to counter the roll would have been ignored by the simulator’s computer. Only after the simulated airplane reached a pre-set roll angle did the computer allow the pilot’s corrections to be applied. In all situations, the roll correction with just the ailerons (as most pilots initially attempted) did not work. Well, it didn’t work because the simulator was programmed to not allow them to work. When the pilot saw the inability of the aileron controls to be effective, he applied the only additional control available – rudder – which each pilot used, sparingly, I might add, and, if I may offer a speculative comment, probably out of anxiety and frustration. In a fully responding simulator or airplane, the pilot would have recognized the effectiveness of the aileron to counter the roll and if the upset was sufficient to cause the roll to continue with increasing aileron application, I think it prudent to, at that time, add a rudder input. But, as our PF recognized in the first encounter, use of rudder was not required.
That brings me to you point about whether of not the PF thought the second encounter was “more” than the first. The FDR seems to refute that idea. However, we know that the PF was a bit concerned about the potentials of following the heavy JAL B747. I direct your attention to the CVR where he queried the Captain regarding the ATC supplied separation at takeoff; “you happy with that distance?” When the Captain indicated that it was “OK,” the PF queried him yet again; “so you’re happy?”
I think the PF was nervous about the JAL B747 – probably more nervous than the Captain or you or I would recognize. I think the first wake encounter (handled nicely by the PF) merely made him more “on edge” in anticipation. With the on-set of the second encounter, I think the PF’s self-control was severely taxed, and he over-responded physically while trying to
sound like he had everything under control.
However … you may be correct. Perhaps we are destined to agree to disagree on the finer points of this particular accident. Let me say though, I have enjoyed reading your thorough and thoughtful comments. I hope all of us in the industry have learned from this accident and all the discussions that have taken place as a result. AND, sir, let me say that I would be proud to share a cockpit with you any day. Cheers!