I don't think the FO did that because the captain would have stopped him if he did. Would any captain let his FO do this? I wouldn't. We had an A300 have out of control rudder movements landing at MIA and both pilots felt they were going to crash prior to this event.
We have two very different situations :
- The flight AA587 was tooken in a heavy and quick wake turbulence and the first officer did that violent pedal sharing very quickly - probably the captain had feet on the ground and could not avoid his FO pedaling quickly enough. It is a non pilot induced big oscillation of the airflow where the A300-600 had a stable dynamic, followed by a pilot action near of shocks giving excessive conventional aerodynamic forces.
- In the both cases with Yaw damper failure, the possibility of DUTCH ROLL is important. You avoided it on your B727. Your friend and his Captain had less chance and developped the dutch rolll which is a resonance between the airflow movement around the whole aicraft and action with roll and/or rudder of the pilot to stop that PIO - inadequatly because the dutch roll is not taught to pilots nore described in ATPL books, where the problem is described as non existing with the yaw damper . But dutch roll may start by other initial disturbation - pushing one pedal violently (..in a sim is safer
) - and the pilot feeds himself the resonance acting on the stick and pedals AT THE WRONG MOMENT AND WITH INADEQUATE SPEEDS. A good aerobatic flight culture may avoid/correct that resonance without equation, but it may be solved,
in flight, by equations too.
About the SOP, I already told that Learjet had elaborated that poor and dangerous method of rapid pedal sharing movements after years of fears and some accidents to try to stop their genetic dutch roll. As nobody around the world wanted to teach pilots about dutch roll and other PIO - labelled as "pilot FAULT" and sometimes "human factor" (sic)
- in case unions would use it anyway, that bad bar SOP was used - around the world in our lovelly international community
- against any unwanted oscillation and turbulence ,and perhaps applied in the Queens accident AA587.