In answer to the various posts:
The Right Hand Seats left hand wasn't anywhere near the collective when the bounce started (as he had relaxed by then).
The Pedestal Master Force Trim switch was on but can't vouch if during the bounce I pressed the cyclic FTR button.
We don't fly the a/c in ATT mode except on long IFR transits.
Will find the exact Honeywell AFCS Model and Mod state and post it.
Other thoughts from a senior 412 operator were:
The Heads Pendulum Dampers could possibly set up a bounce if harmonised to the ?Hz oscillation. 24lb per blade root is enough mass to create a bounce.
My thoughts were- 'but why would engaging the AP damp it out?'
Still confused but 'good ideas club' inputs are heartily welcomed.
