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It's mechanical linkage from the throttles quadrant, no relays, and it works off of oil pressure flowing thru the mechanically linked valves.

The main use is for short field braking or stopping distance. I've got a lot of time in King Airs and used it a lot. It saves a lot of wear on brakes and disks.

If it's ever used on the ramp area, the FBO will not want to see you again. If you run Garrett's, they don't want to see you anyhoo.

It's mechanical linkage from the throttles quadrant, no relays, and it works off of oil pressure flowing thru the mechanically linked valves.

Thanks for the info, blackdog. I concluded that prop-pitch was controlled by electric actuators because I've seen so many "prop pitch motors" for sale in surplus catalogs. Obviously, just because some props are controlled by electric motors doesn't mean they all are.

I guess the mechanical linkage makes me feel a little better, because it can't go into a failure state just due to some little piece of dirt or whatever. Still, hydraulic valves can fail...

Well, I guess there are a lot of things on an airplane that will kill you if they fail. Prop-pitch control is just one item on the list.

(steely)