Spitfire IIa prop pitch

[Crumpp]

I think the confusion comes from the fact the propeller is electric. An electric motor is what changes the blade pitch.

The motor is operated by a hydraulic switch in normal operations and functions as a CSP. The hydraulic's reads the engine rpm and converts it hydraulic pressure with a regulator. That pressure then operates the electric motor to adjust the blade pitch to maintain the calibrated rpm. This way, both engine and propeller can be operated with a single lever in normal operations.

In an emergency, the pilot can manually operate the electric motor to change the blade pitch to maintain rpm or feather the propeller should he lose hydraulic pressure.