Originally Posted by OC
Machinbird
Whilst I do not doubt the phenomenon exists I was reading your post as an indication that you believed the design of the sidestick played a part for inducing the oscillations. This is what I was questioning. All evidence from the Airbuses flying is that the sidestick is a reliable and useful input device with very little in the way of vices. The more I see of the evidence the less it appears that the machine had any role in the accident. There is no 'smoking gun' as it were; just pilots who were not adequately trained or prepared for what should have been a recoverable situation.
Let me re-state the theory (And at this point it is just a theory.)
[theory] The AF447 PF made too large of an initial lateral control input and ended up sending the aircraft into a roll oscillation which can be seen in in the BEA charts. He attempted to 'get ahead' of this oscillation by making even more rapid control deflections, but ended up continuing to drive the oscillation. In his frantic attempt to move the stick even more rapidly against the drag of the roll viscous damper, he brought the canted forward stick back from neutral into the nose up direction to obtain better mechanical advantage (since the stick being vertical gives him a greater lever arm). This response would be automatic if he was concentrating on his roll control problem. [/theory]
I agree that the sidestick can be an accurate, useful, and safe means of control. However, the A320 does have occasional problems with roll PIO. Perhaps the A330 does as well in the correct circumstances-like in roll direct mode at altitude.
When a pilot encounters PIO, one of the natural reactions is to believe that the control system is malfunctioning. Most of us would find this extremely disconcerting. It would be good for a double dose of adrenalin.
An experienced pilot would change his control strategy to break the oscillation. An inexperienced pilot would likely continue the oscillation until he tired of the effort of driving it. That is what the BEA charts seem to indicate. (And as the roll oscillation began to get under control, so did the nose attitude.)
PIO is a complex condition and should not be blamed on just the sidestick design. If roll PIO was a player in this accident, then the fixes are relatively simple. Roll direct is an infrequent operational mode. Roll direct at altitude will be even scarcer. It is entirely possible that only a small percentage of pilots employ "high gain" control strategies that would trigger a roll PIO. BTW the C-17 aircraft was very late in its development cycle before its roll PIO characteristic was identified and corrected.
Training to avoid "high gain" control strategies would help pilots avoid PIO. Perhaps we need a PIO training device to teach pilots how to avoid it.
Meanwhile, "mayonnaise stirring" should definitely be avoided on Airbus type aircraft.