What action is taken by the CSU when the propeller is in underspeed condition?

When the propeller is in an underspeed condition, the Control System Unit (CSU) takes the action of decreasing the blade pitch to allow a higher RPM. This is based on the principle that a propeller with a lower pitch angle will produce less drag and allow the engine to spin the propeller faster.

In an underspeed scenario, the propeller is not turning at its expected RPM, which can happen for various reasons like insufficient power or improper control of the propeller pitch. By adjusting the blade pitch to a lower angle, the system decreases the aerodynamic load on the propeller, enabling it to gain RPM. This action is crucial for restoring the propeller's performance and ensuring the engine operates efficiently.

In contrast, increasing oil flow to decrease pitch for lower torque would not effectively address an underspeed condition, as it does not directly contribute to increasing RPM. Increasing blade pitch to reduce RPM would exacerbate the problem rather than alleviate it. Stopping the engine completely is an extreme measure and would not be the immediate response to an underspeed condition, as maintaining flight operations is typically preferred when the system is capable of recovery.