Seafuryfan,
How grossly does one have to fly out of balance to induce yaw/roll divergence?
It is not strictly the out of balance that causes it, but an inappropriate yaw input to correct the out-of-balanceness(?).
The roll rate induced can be in excess of the ability of the cyclic to overcome it, and substantial height loss can ensue, but it takes a very large, rapid and sustained application of yaw pedal to get that sort of reaction. It is demonstrated very early on in the Puma OCU course, as an example of a. one of the Puma idiosyncrasies and b. gross mishandling. For the QHIs who demonstrate it one of the most tricky bits is overcoming the instinctive reaction to apply top/opposite pedal too quickly, before the effect has had a chance to build, which lessens the rather sobering effect of the demo on the student and does not give a chance for the student to fully see how quickly top pedal recovers the situation. In summary, if you manage to induce yaw/roll divergence, you have either a. done it on purpose, or b. grossly mishandled the aircraft. Pretty sure this has nothing to do with this accident.
I believe the one lost in France was being flown by a Boscombe crew who were investigating just that phenomenon.
If you were thinking of asking "how does yaw/roll divergence work?", don't go there!