[JJink]

Originally Posted by Roger, Roger

Uh...that's almost completely wrong.

Yes it is.
NTS on 331 is there to assist the pilot in feathering the engine after loss of power (giving him some reaction time). When the engine quits and the airflow turns the prop the ring gear inside the gear box moves up actuating the NTS valve allowing oil to route out of the prop (beta tube) and let the counterweights and the spring start moving the prop in the feather position. The prop will not feather by its own so the pilot still has to do it.