In addition to all the above, on the 412EP fitted with AP (as opposed to Helipilot) with Flight Director and Coupler, the Coupler heading hold stops working below 60 knots.
This is, in my experience, a common cause of total loss of control during the final stages of IFR approaches even with experienced (but rusty scan-wise!) IFR Captains (luckily in the Simulator on all occasions that I have witnessed)
In particular whilst flying a fully coupled IFR approach single engine with visibility at or below minima with a "must land regardless" emergency (e.g. Baggage bay fire or insufficient fuel for a go around) I would recommend holding IAS at or slightly above 70 kts (top side of the minimum power curve) since even a minor scan hiccup allowing speed to fall slightly below 70 kts will result in a rapid further decrease in IAS (as the power requirement increases) resulting in IAS falling below 60 kts, then heading hold ceasing to work then usually disaster (simulated)
