The NTS system on the TPE-331 and other turboprops takes the propellor to a low drag "windmilling in the NTS mode" as the TPE-331 folks say it in very short order...the performance figures for engine out ops is based on this configuration as opposed to the prop being fully feathered...the big advantage to this system, is if the engine were to relight, the propellor quickly returns to prop governing mode, and presto...engint thrust is once again available..if the prop were fully feathered, this would not be the case... some of the larger engines... allison 501/t-56 engines use an autofeather system during takeoff and landing, and rely on the NTS system during other phases of flight..the "auto-coarsen" system while mchanically different is along the same lines of the NTS system...the beauty of an nts system is it requires no electrical power whatsoever..and allows an engine to relight and go on about it's business in the event of sudden flameout..if the engine is mchanically unable to do so, then subsequent checklist procedures call for finishing the job and feathering it manually..hope this sheds some light on the subject...