Stuck collective - fairly easy to recover from and practice. Get on the backside of the power curve and down you come.
Does this work? We practised this on my FI course, and it didn't seem to. I was asked what I'd do, and said the same as vaqueroaero - but I tried it and we didn't really come down, or not much anyway. Mike Green showed me what he'd do - he closed the throttle a bit, at the same time putting the helicopter into a turn to raise the rpm. This brought us neatly down, turning in circles, adjusting throttle and turn as we went. I know we levelled out and did a run-on landing, but I can't remember exactly how...and early on a Sunday morning I don't feel like working out the theory; anyone know?