The article posted by Retired F-4 draws heavily on the National Research Council book on PIO that I have recommended in the past. (National Research Council. Aviation Safety and Pilot Control, 1997) For one with an understanding of aviation and the concept of feedback loops, it is an easy read, and as a soft cover version, is very affordable.
I use the term PIO because that is what I am comfortable with, but I interpret it as Pilot in the Loop Oscillation. PIO cannot occur if you are not exercising direct control.
I recently had a message from a tactical jet pilot describing a PIO incident he experienced. He stated that he was too busy during the incident to communicate with his back seater in any meaningful way. The workload was so high that he had no spare capacity to communicate! Can you see the relevance to the AF447 cockpit scene?
Yes, AF447 was not in a PIO when it departed from controlled flight, however the PF had just been through 30+ seconds of hell that shook his faith in his aircraft's control system and fatigued his mind. At the same time, the PIO incident had set him up for a stall by stealing his airspeed and leaving him in a nose up attitude.
Why didn't he control the nose attitude you might ask. The simple answer is that he didn't have the attention to spare to adequately perform that task. He was concentrating almost exclusively on the roll channel and I believe was already tense and nervous before the autopilot dropped out which caused him to pull the stick back unconsciously.
In the main AF447 threads, a gent who goes by the handle "grity" prepared several charts of stick motion for the first few seconds after the autopilot dropped. The following chart is the best of those:
The numbers on the move lines correspond to the time in seconds after time 02:10. Bonin took control at time 02:10:07.
If you will notice, the majority of the first 11 seconds that the chart covers was spent in the 4 to 8 degree back stick range and only toward the latter part of the period does Bonin provide a couple of pulses in the nose downdirection. For the first 9 seconds he is just banging the stick from side to side while holding it fairly consistently in the 4 to 8 degree aft stick range.
Here is what these roll inputs did to the aircraft:
As expected, there is still much skepticism about what PIO had to do with the loss of AF447.
Simply, that type of input at cruise speed is overcontrol, not to be confused with PIO.
There is a simple difference between overcontrol and PIO. If you know you are overcontroling you can stop.
If you are in a PIO, you see the situation as the aircraft
fighting your control and you cannot stop because you must keep the aircraft under control.