Sprag clutch freewheeling unit 

You are so welcome! Thank you for the suggestion.

you can see it in real if you open rear bike wheel-same thing, free wheel

You are welcome. Regarding the oil pressure. I m not sure where someone got the 10 seconds time from. There is nothing in any publications that says that. But I do have references from pilots that continued to fly after the loss of oil pressure. There was an accident in Canton, MS where the helicopters engine routed all the oil into the exhaust due to a plugged oil line. The ENGP light illuminated and because the oil temperature was not rising the pilot concluded that there wasnt an issue (oil temp would actually go down after a loss of oil flow). The helicopters engine ran for 26 minutes before failing. Hard landing.

@@EUROSAFETYTRAINING Insteresting, if I remember correctly, that number came during training in an Astar simulator somewhere in Western Canada. Whoever the training was from (I'm not sure if it was directly from Airbus or not) simulated Eng Oil low and a failed freewheeling unit, and the conclusion was there was 10 seconds to failure w/o Eng oil pressure. I'll need to look into where/who they got that from. Can you say as to why the manual says the engine should be shut down if loss of Eng Oil is confirmed?

So looking into it more that 10 second number came from an Airbus certified simulator in Edmonton, Alberta. I’m curious as to where they got that number from

I appreciate that!

To be more clear ... the drive goes through the engine. The engine has an output shaft that sticks out both ends of the engine. When the engine is running a freewheeling unit around the shaft powers it, and then of course that shaft powers the transmission and tail rotor. After an engine failure in an auto the main rotor turns the transmission, which turns the engine to MGB drive shaft, which turns the output shaft in engine, which powers tail rotor drive shaft, which powers tail rotor.

@@EUROSAFETYTRAINING Awesome thank you for the reply! I think my confusion on the original description was that the MR was somehow still fighting with the resistance of the dead engine while powering the other systems. Sprag clutches are very cool. Side note; during an auto, is the MR also powering the instruments (through the alternator) or are they just running on battery at that poin during auto rotation?

The connection between the main gearbox and the tail rotor runs through just the engine's gearbox, which is packaged with the engine and so is considered part of the engine... but of course it's not really the engine.

@@brianb-p6586 thanks Brian this was the clarification I was looking for!

Yes they are complete separate within the engine

@@EUROSAFETYTRAINING thankyou very much

Are you being sarcastic?