Originally Posted by
Willit Run
"FDR data further
indicate that when the stick shaker activated, there was a
25-pound pull force on the control column, followed by an up
elevator deflection and increase in pitch, angle of attack."
Kind of wondering why the "pull" on the control column, and not a "push"??
When a stick shaker goes off, that should indicate that anymore pitch UP would exacerbate the situation.
It'll be interesting.
it's not uncommon for column force instrumentation (at least on test a/c) to register a "pull force" when a stick pusher fires, because it's practically impossible to instantly release the column, and so the pilot's hands, inevitably, resist the push, which will be picked up as an apparent pull force, opposing/slowing the pusher.
It's not clear from the quote about the FDR whether it's an instantaneous pull or a sustained pull; the former would be consistent with a puilot briefly re4sisting the push and then allowing it to do its job, the latter would indicate sustained resistance to the pusher.
It's also very difficult with the frequency of most FDR control force parameters to pick up a true instantaneous force - so the actual force may have been higher (a similar issue is routinely encountered when trying to assess how "hard" a "hard landing" actually was, for example)
Given that pusher systems typically are designed only to apply force in one sense, mechanically, and to release in the other, it'd take a considerable amount of ingenuity to rig one backwards and not notice. Certainly some pusher equipped a/c have pusher tests where it would be extremely obvious that this had been done; I don't know if the dash 8 is one of those, though.
Edit: apologies, I answered that as if it were "pusher" but as pointed out below, the reference is to "shaker".