Just further to my previous comments about FMS that allow pilots to decide if they want to shut down or retard and engine(on the BK 117).....The SA 365C1 I am flying has the option written into the emrgencies section of the flight manual itself.
For the C models with overspeed protection fitted, the Flight Manual states "For engine not fitted with OVERSPEED LIMITERS-shut down relevant engine immediately".
It doesn't actually state why, but having just spoke to the engineer he informs me that OLDER Arriel engines had a penchant for the intermediate pinion in the Module 5 letting go. This happened on a Squirrel in Tasmania some years ago. This would cause the NTL or free turbine to overspeed as it stops driving the fan. The Overspeed protector shuts down the engine immediately this occurs. Don't know if its a good thing or not letting it get that far if you have preliminary warnings that the free turbine is about to s**t itself via the chip light coming on. Don't need it letting go and taking out the good one. But, it is fitted and gives the pilot the option.