When is a propeller considered to be in overspeed condition?

• A. engine RPM drops below idle
• B. centrifugal force acting on the governor flyweights overcomes the speeder spring tension
• C. the propeller pitch locks at high angle
• D. the oil pressure exceeds maximum

Answer: (B)

Constant-speed propeller governors regulate RPM by balancing centrifugal force on the governor flyweights against the restoring force of the speeder spring. As RPM rises, the flyweights generate more centrifugal force and tend to move outward, which shifts the governing mechanism to reduce fuel flow or increase blade pitch to slow the engine. The speeder spring provides a counteracting force that resists this outward motion and helps keep the RPM at the set value.

Overspeed happens when the centrifugal force on the weights becomes greater than the spring’s tension, so the weights move to a position that cannot restrain the speed. In this condition the governor can no longer hold the prop at the commanded RPM, and the engine RPM climbs beyond the maximum limit.

Other conditions described (RPM dropping to idle, a lock at high pitch, or oil pressure exceeding a limit) do not reflect the governor losing control due to flyweight overtake of the spring, which is the defining moment of an overspeed.