Constant Speed is probably what I was thinking of. And speaking of multi engine failure, you’ve just reminded me of the demise of TransAsia Airways Flight 235 where the right engine feathered itself erroneously, but then the crew misdiagnosed the situation and shut down the left engine. Mentour Pilot made a video on that particular accident.

I like this answer. The only thing I would add is that when the fan blades are all stalled, it might seem then that drag and energy consumption should reduce, since there’s not much air moving. But in a cruel twist (fan pun intended) of aerodynamics, the useless spinning of stalled fan blades still causes parasitic drag. So not only does the fan not move air, it’s also consuming more energy than spinning a solid disk of the same moment-of-inertia.

When the engine fails for certain single-propeller aircraft, there’s sometimes a mechanism to lock the propeller to make it stop rotating, since it would otherwise “windmill” in the air and waste the precious kinetic energy that’s keeping the plane aloft. Or so I’m told.