BOAC;
Re #83,
The wmv shows rudder movement in line with pedal displacement until the supposed 'separation', but is that supposition or confirmed?
Animations are not strictly investigative tools in the sense that they should be relied upon to determine what happened when. Animations are used to provide situational awareness from which an examination of the actual data can be launched.
The "draw" of animations in a visual, (non-textual) culture such as ours is psychologically very powerful. The format does
not invite examination. Rather, for non-specialists especially, the "agenda" of such animations "convinces" rather than "raises questions".
Except for, "because they can", I am not certain of why animations have become part of the "investigative" kit at all. They are helpful in the act of imagining either the airplane or the cockpit indications but there are problems with using animations for detailed examinations such as the kind often suggested regarding the rudder and rudder pedal symbols' motion. I have posted my comments numerous times on these problems in hopes of placing the animation tool in appropriate perspective. Animations may be useful to "place context" but should not be relied upon for detailed information or conclusions.
The reason for this lies in the way flight data is recorded. Very simplistically but importantly, there are two problems: 1) within the one-second recording time frame, dozens if not thousands of parameters are recorded sequentially and not all at once, and, 2) each of these parameters is recorded at an instant in time and most of the time, (the rest of the second), is not recorded. There are exceptions to the "once-per-second" recording - Vertical 'g' is usually recorded 8x per second, etc.
But, stating it differently, most flight data is collected at the rate of one "snapshot" per second. Within a one-second time frame, thousands of parameters sequentially take their place in the dataframe until the beginning of the next second.
These one-second digital snapshots are placed in a dataframe one after the other, so to speak. To re-emphasize, the parameter that may be recorded at the precise beginning of a second, let us say,
rudder pedal position, will come slightly before the parameter, let us say,
rudder position, which is recorded, in its turn, slightly past the precise beginning of that second, and so on, through thousands of parameters.
But because animations are mathematically smoothed to avoid an inherent jerkiness from digital input which has more periods of "no-data", than not, assumptions are made by the animation software designers about "what happened in the spaces where there is no data", and so data is filled in where there is none.
Think of one stroboscope when observing the motion of just one thing in the dark - while the strobe is lit, we can see what is going on with the control or indication under the strobe-light, but once the light is out, nothing can be determined for sure even though we may be tempted to interpolate "between data points".
Most of the time such interpolation is innocent and usually does not lead to mistakes in understanding what happened.
But in swiftly-occurring events such as a hard landing where examination of both 'g' and flight control surfaces would benefit from a "frame-rate closer to video", we are stuck with interpolation of parameters sampled at only 4x and 8x per second. Thus, when the "strobe is off", we are "in the dark" about where the sidestick was, or what the rate of descent was, in-between samples. The same may be said even more so with parameters which are only sampled once-per-second.
The assumption implicit in a casual reading, (an animation) of the data is that "things happened at the 'same time' ", when in fact they may not have, and incorrect conclusions may be drawn when only looking at an animation. Thus the advice to be cautious when watching an animation of an incident or accident. We just do not know what went into the animation to make it look the way it does. Within such animation programs are dozens of corrections to wind, to magnetic variation, to rates of descent and so on, which are available to the analyst and which, when used with intelligent comprehension of the event achieved through close examination of the actual data, can reflect, within the limits of the technology, what happened. But, despite what the Discovery Channel teaches, animations of incidents or accidents are only rough approximations, and are not videos of what actually occurred.
So, for detailed understandings, I would readily dismiss the animation of AA587 except as a general, situational tool and I would avoid drawing the conclusion about rudder pedals and rudder positions until the actual flight data was examined. We don't even know if the rudder pedal position "parameter" was merely derived from the rudder position, (such derivation is not unusual but is in my view a waste of time and calculating capacity), and not an independent parameter. I have been unable to locate any DFDR readings and none is provided in the NTSB report.
That all said BOAC, in response to your question, I think it is reasonable to conclude that fins don't just come off airplanes without cause. No plausible alternate theory as been posited which places the departure of the fin prior to the rudder inputs.
PJ2