How big were the roll oscillations? That, in hindsight, was the interesting bit
...The trace showed a max on the final excursion of merely a tad over 10 degrees, but given the circumstances (night, somewhere on finals) and above all the abruptness of the control reversals it felt like a heck of a lot more....I would hate to experience a roll PIO that really got going...
I would like to point out to the casual observers here, that the PIO here that Wiggy described was less in amplitude than the AF447 initial roll excursions (if I correctly understand the meaning of the 10 degree roll readout of Wiggy's example.)
One way a problem can occur is when the flying pilot tries to zero the roll
rate rather than just bring the wings back to level. When the roll rate is high enough, the eye is drawn to the motion and it is easy then with a large, inherently slow rolling aircraft to predict the roll rate and provide a synchronous opposite phase aileron input. When you start responding to rate signals though, you advance the timing of your control inputs by 90 degrees of phase angle and this has the effect of driving an oscillation. You can see this effect in the chart I posted here:
http://www.pprune.org/tech-log/53975...ml#post8868131
There have been tests run on the threshold roll rate needed to trigger a roll rate cancelling response from a pilot. From memory, it is in the 10-11 degrees per second rate which AF447 achieved in its initial roll oscillations.
I would hate to experience a roll PIO that really got going..
I would like to echo that comment. Until you have experienced a PIO/APC event, you cannot imagine the impact it can have on your ability to control the aircraft.