Clandestino wrote (about PIO/APC) :
There is not in yaw.
To have PIO/APC you have to start with pilot's oscillatory input. Rudder starts to oscillate without pilot's input at about 2:11:45 (following yaw damper commands) when the aeroplane is so deeply stalled that high AoA and low speed make it pretty inefficient.
Indeed, when the aircraft is fully stalled and mushing, and PF is holding full deflection left-up on his sidestick, and he is not touching the rudder pedals, yaw damper does give orders. After some time looking at these traces, I still cannot make sense of them. This is an area of interest which I hope will be investigated.
However, more akin to the APC definition which you suggest is the start of the sequence, right when PF takes control. Roll and yaw are mixed up in an oscillation, which appears to the pilots as a pure roll movement, but where in fact rudder is actuated and lateral accelerations are measured.
Surprisingly, no trace of gyros is provided. Yaw rate gyro would be interesting to look at. Heading traces are insufficiently detailed to extrapolate yaw rate from them.
Moreover, I am greatly interested in aileron authority and response to SS inputs. It appears that right inboard aileron maximum deflection remains limited to a modest amount. This maximum available deflection decreases significantly within the first seconds after A/P quit. Such limitation is surprising in the context of a Direct Roll flight law, which is part of Alternate 2B global flight law.
Interesting elements of comparison are available with the D-AXLA accident report. FDR traces show a large number of fascinating bits of information. Such are not provided in the 3rd interim report which is our subject matter. Maximum aileron deflection appears different in this report. However, the exact type of aircraft is different of course. Expert input welcome.