FAA Aviation Mechanic Powerplant (AMP)PropellersMedium
During a ground run, a constant-speed propeller governor's flyweights move outward due to increasing engine RPM above the selected setting. What action does this cause?
- AThe flyweights lock the propeller at its current pitch until RPM decreases naturally
- BThe pilot valve moves to direct oil to decrease blade pitch, further increasing RPM
- CThe flyweights signal the fuel control unit to reduce fuel flow directly
- DThe pilot valve moves to direct oil to increase blade pitch, which reduces RPM back to the set speed
Show answer & explanationAnswer & explanation
Correct answer: D. The pilot valve moves to direct oil to increase blade pitch, which reduces RPM back to the set speed
When engine RPM exceeds the governor's set speed (overspeed condition), the flyweights move outward against spring tension, repositioning the pilot valve so oil is directed to increase blade angle (pitch). Increasing pitch increases the load on the engine, bringing RPM back down to the selected value.
Why the other options are wrong
- A. Governors do not lock pitch; they continuously modulate it.
- B. This is the opposite response and would cause a further overspeed.
- C. The governor controls propeller pitch, not fuel flow, to control RPM.
Governor Flyweight Action
Centrifugal force on governor flyweights repositions the pilot valve to control oil flow to the propeller, adjusting blade pitch to maintain selected RPM.
- Overspeed: flyweights move out, pitch increases, RPM decreases
- Underspeed: flyweights move in, pitch decreases, RPM increases
- Governor spring opposes flyweight force to set desired RPM
Memory trick: Overspeed weights fly OUT, pitch goes UP, RPM comes DOWN