Make a parabola. Draw X-Y axes.

Glue the parabola (on its side, like that, er familiar shape) to the "wall" == Y-axis, about 60' up, on the scale you've also drawn. The tip at right is (used to be) ~60 mph on your X-axis scale.

Inside that area, generally you be daid if it quits.
If you're moving horiz. faster than 60 or so, then the air below you
(already compressed away by rotors, thus unable to provide static air-mass for autorotating) is not a problem.. and you can glide.

ie. precision hovering, below the ~60' alt. is the absolute worst case scenario if engine failure. (At somewhere beyond 150ish? alt. apparently you can still achieve autoration, if all design features were just right.)

All depends on your adoration-level of the God of Technology / and how many of its -ologists you think -?- are/were fully conscious, while at work. Eh?

On cycles - I've always inspected tires on up, before every ride \ufffd l\ufffd any old jet jockey with a checklist. It worked. So far -

Now with all the fiddly bits in and outta sight on a rotary -- crap shoot. Y'aint gonna find bad U-joint #43. I'd still kill for a ride in the Carter Copter If Ever ... Doug Marker manages to get one up to SR airport. :-)