Feathering a propeller.
I've done it in FSX, but only to see the blades turn.
But lets face it, being a real pilot in a real plane, it's something that they need to know, no matter how un-often it's needed in real life.
Accident: TAM F27 at Guayaramerin on Dec 10th 2013, bird strike
"The damaged propeller caused the airframe to vibrate. The aircraft returned to Guayaramerin for a safe landing about 15 minutes after departure."

But lets face it, being a real pilot in a real plane, it's something that they need to know, no matter how un-often it's needed in real life.
Accident: TAM F27 at Guayaramerin on Dec 10th 2013, bird strike
"The damaged propeller caused the airframe to vibrate. The aircraft returned to Guayaramerin for a safe landing about 15 minutes after departure."

) the engine would breath just
...!