What corrective action should you take if the rotor RPM falls below the green arc and you have power?

When the rotor RPM falls below the green arc and there is available power, the appropriate action is to add throttle while simultaneously lowering the collective. This combination works to recover and stabilize the rotor RPM.

Adding throttle increases the engine power, which helps address the reduced rotor RPM by providing more energy to the rotor system. Lowering the collective reduces the pitch of the rotor blades, which decreases the load on the rotor system. This helps to prevent further RPM drop by allowing the rotor blades to operate more efficiently given the reduced power availability.

In some situations, simply increasing throttle without adjusting the collective might only exacerbate the problem, as the increased load could further decrease the rotor speed. Similarly, increasing collective while reducing throttle could lead to further rotor degradation as power demand increases. Increasing forward cyclic to gain speed is more applicable to different flight scenarios, and immediate landing is usually a last-resort option; it would not address the immediate concern of restoring rotor RPM while power is available.