NTS 331
Having spent many years building the 331 I thought I would give you fly boys some hard facts about the NTS system
The NTS system is purely a drag reduction system, it will not auto-feather. On an engine failure or flame-out the prop will now drive the engine. This is sensed by the NTS (negative torque, the clue is in the name) system and it will dump oil pressure out of the prop and it will start to move toward feather. However, once the prop moves toward feather it is now no longer driving the engine so the negative torque is no longer sensed and the whole system resets and the prop moves away from feather in an attempt return to the speed currently set on the prop governor, for landing 100% (remember it was never feathered anyway). If auto ignition is fitted it would be triggered by the NTS system and hopefully relight the engine. If auto ignition is not fitted or does not succeed the engine will remain in the NTS mode until a manual feather is carried out by the crew. As has been mentioned, the prop must be placed onto the start locks during normal shutdown. If this is not done the prop will slowly creep toward the feather position due to internal leakages, so in the case of this accident, even if both engines were running at the time of the crash, both props will feather once stationary (internal damage excluded) Obviously, none of this would be the happen in the case of a catastrophic failure of the engine, prop or gearbox