When I did my Bell 214B conversion in Oman, the QHI warned me about rotor decay in the event of engine failure, 33 inch chord blades, remember!!
At 120 knots in the cruise he told me to be ready to lower the collective and to watch the rotor RPM as he counted down to the "engine failure" and chopped the throttle. As I lowered the lever very quickly I watched the RRPM decay instantly to 85%.
Some time later whilst carrying out a topping check at Seeb International I had an engine surge whilst climbing at a great rate of knots and before I knew it, I had closed the throttle, lowered the lever, rolled on some bank and applied aft cyclic to load the head and put out a mayday call. The rpm were still in the green but the engine wasn't very happy as part of the bleed band had gone through the compressor, so I had to shut it down for an engine off landing back onto the main runway. I then discovered, at 5000 ft in the descent, that the auto rpm were outside limits, a little too low for the AUW, which did make an interesting approach, i.e. a little faster than normal with a slightly exaggerrated flare to recover them, followed by a run-on landing without any damage to the aircraft.
Incidentally, there was a rate of climb limit in the Flight Manual, not to exceed 2000 ft/min below 2000 ft agl and during the above, I was well over 7000 ft climbing at 4000 ft/min. Interesting day...........