For what it's worth, when I informally checked out in the AH-1G Cobra circa 1970 (long story, begins with a missive that started out "Your friends and neighbors...), it was made clear to me that if the engine quit while we were in cruise flight (which was pretty fast but to my surprise not as fast as a lightly loaded Chinook), I was not to immediately lower the collective but simply to keep the thing straight and level for a short while without moving the collective (exactly how long, I don't remember), wake up the pilot in the back seat, and then lower the collective. This suited my helicopter flying aptitude since I pretty much knew how to work the cyclic and pedals as a 1,000-hr fixed-wing pilot and flight instructor, whereas my response to a unexpected helicopter-engine failure from a collective standpoint was usually "Whut?" followed by a dawning realization that the sound of the rotor was changing. (That reaction time also stood me in good stead for engine failures in a hover.)