I have been following this thread with mostly a casual interest, until I read this.
I've been doing this long enough, especially as an MEII to tell you that LAST thing you do is take up Jets and Tprops, and do shutdowns......flight idle simulates a feathered prop or a dead engine just fine.
To prove this point Guppy has only to provide the name of ONE training provider, that takes up real Jets and Turboprops to perform shutdowns, taking the chance with million dollar gear to fly around on one engine, cavitating the mechanical fuel pump for training purposes.
I will readily admit that I have not flown a turbo-prop in quite some time. However, when I attended MU-2 training at Flight Safety International we did, as part of the in-flight training program shut down an engine in flight. This was done to demonstrate the NTS, Negative Toque Sensing, system on the engine. Please note I said engine, not aircraft. All TPE-331 engines have this system no matter the airframe they are installed on.
The NTS demonstration was performed around 15,000. The CRS switch is moved to the stop position shutting the fuel off to the engine. Almost instantly the propeller would go to a near feathering position, about 90% (or somewhere near that figure) of full feather. Then the pilot would complete the total feather procedure by feathering the prop.
Therefore, even though I am not Guppy, I have provided the answer you requested. Yes running engines on actual aircraft were intentionally shut down by shutting off the fuel to the engine and the school was Flight Safety International.
You have heard of Flight Safety International, have you not?
Oh, the turbo-props I have flown are; MU-2 J-K-L-M and Kingair 90s-200s.
One more point. You are aware of course that you can start a PT-6 and prevent the prop from moving, either by using an installed prop brake or tyeing the prop down where it cannot move.