Originally Posted by
Mr Optimistic
As a layman that's exactly what I would have assumed. Is it possible you could explain without undue effort?
No problem at all.
Helicopters, like aeroplanes, maintain a degree of stability due to the airflow passing over their aerofoil surfaces. For an aeroplane, the lack of airflow over the wing will lead to stalling (and severe instability). The lack of airflow over a rotor disk won't lead to a stall in the same sense but the aircraft becomes much less stable and relatively harder to control.
Therefore, all IFR rated helicopters have a Minimum IF speed (ie a minimum speed that must be maintained whilst in IMC. Depending on the type, this is normally 50 to 60kts. I don't know that the VMinI speed for a S76B is though, I'm afraid).