I shall try and explain my stand on why I do not full feather engines for the sole purpose of demonstrating to a student that a certified feathering device does in fact work.
First allow me to point out some facts regarding the instance where a propellor did not unfeather during a practice feathering session just recently.
(1) I have no idea at what altitude they feathered the thing, however it did fly to an airport on one engine because they had feathered one and it would not unfeather.
(2) The airplane was in excellent mechanical condition because it had been worked on for several years during the restoration process.
(3) The Engine had just come out of a major overhaul and had less than 100 hours on it. Also the propellors had been overhauled and new blades installed.
(4) No it did not have unfeathering accumulators on it, it was a radial with an electrical driven feathering mechanism that is independant of the engine driven accessories.
When discussing flight training we should bear in mind that there are many different mechanical / electrical methods of feathering propellors and in fact some props can be feathered and the engine is still running such as the P&W PT6 for instance.
I personally have almost bought the farm on two occasions because I feathered an engine and it would not unfeather.
So I got to thinking about it and decided that I did not want to go for three strikes and you are out, therefore I will not feather unless there is no other choice other than a mechanical need to.
If we use the mindset that a student must experience the sensation and sight of a fully feathered propellor or he/she may freeze when a real emergency developes then why not demonstrate flight above VNE until we reach the flutter realm of the structure?
After all we have only read that VNE and flutter exist therefore why not demonstrate it just to prove that it will happen?
Each of us must decide where our comfort and safety limits are and using that baseline develop a system of instruction that teaches the student the art of flying ,... safely,... that I have tried to do during my career and so far my students have demonstrated that they have what it takes to grab the bull by the balls in an emergency and pull that feather lever, or push that button for their first look at a feathered propellor, but only when there is a reason to do so..
Those who preach the necessity for full feathering of engines must also realize that they are limiting the conditions wherein feathering can be safely taught...such as during very cold weather in the winter when feathering an engine would be foolhardy to say the least.
So very briefly there are some of my thoughts on this subject, I may not be the greatest of pilots or the best of instructors but I'm still alive to continue on.
Chuck E.