Originally Posted by Owain
What I see in AF447 is a pilot struggling to come to terms with an unfamiliar control dynamic; OK, it is one he had seen before throughout his early career and training, but not one which he had used recently. The (damped) oscillations result from his re-learning process and personally, I think he made a pretty good fist of it. I can't see them as a fault on his part, which describing the motion as a PIO somehow implies.
Welcome back from the fronts Owain.
The definitions of PIO have evolved over time and encompass a broader spectrum of oscillations.
The modern definition of PIO is
Pilot Involved Oscillation and gets away from blame and fault concepts. Without the pilot in the control loop, the oscillation does not occur.
You can bet your money that Bonin was not rocking the wings for the fun of it. From his control inputs, I can conclude that he desperately wanted it to stop. Unfortunately, he chose a bad strategy to stop the oscillation and thus exacerbated his problem. If you look at the oscillation cycles, you will be able to see that there were a number of low points in the oscillation amplitudes followed by an increase in amplitude in the opposite phase to the immediately prior oscillation. To me, this is an indication that he attempted to get ahead of the cycle of oscillation.
To him, it must have seemed that he was a little too late with his control input, so he accelerated his control inputs, i.e. went faster. I think that you can see this pattern in aircraft behavior and in control behavior if you look at the timing on a cycle to cycle basis.
Too bad he didn't have prior experience in flying in Alt2 Law. He would have learned that all he had to do was stop making control inputs.
The development and implementation of Bonin's control strategy must have heavily dominated his thinking and almost certainly explains a lot of the otherwise inexplicably bad flying he demonstrated.
As pilots we learn to put our aircraft under accurate control. When we have an aircraft that is not behaving as we command, your whole attention is drawn to the problem, and it is difficult to leave sufficient attention for other important requirements of flying. The one very short roll PIO I experienced in a simulator was traumatic enough to leave a lasting impression. It compared to the feeling you get when you trip and begin to fall, and you are looking desperately for a hand hold. In my case, I was desperately looking around for a visual attitude reference that did not have a time lag in its display. I am relaying this so that the reader can get some idea of how compelling a PIO problem can become.