If an underspeed trip occurs with rotor RPM, what action should be taken?

If an underspeed trip occurs with rotor RPM, what action should be taken?

• A. Increase throttle
• B. Lower the collective
• C. Apply forward cyclic
• D. Raise the collective

Answer: (B)

When rotor speed drops enough to trigger an underspeed trip, the immediate corrective action is to unload the rotor by lowering the collective. Reducing collective lowers blade pitch and lift, which decreases the rotor’s aerodynamic load and the engine’s torque demand. With less load on the rotor, the rotor RPM can rise back toward the commanded speed, and the governor can help stabilize it. Once the rotor speed has recovered, gradually reapply collective to regain altitude and maintain flight. Raising the collective would increase rotor load and push the speed lower, so it’s not appropriate. Increasing throttle might affect engine power but doesn’t relieve rotor loading. Forward cyclic changes don’t directly address rotor RPM and can lead to undesired flight attitudes while the rotor recovers.

When rotor speed drops enough to trigger an underspeed trip, the immediate corrective action is to unload the rotor by lowering the collective. Reducing collective lowers blade pitch and lift, which decreases the rotor’s aerodynamic load and the engine’s torque demand. With less load on the rotor, the rotor RPM can rise back toward the commanded speed, and the governor can help stabilize it. Once the rotor speed has recovered, gradually reapply collective to regain altitude and maintain flight.

Raising the collective would increase rotor load and push the speed lower, so it’s not appropriate. Increasing throttle might affect engine power but doesn’t relieve rotor loading. Forward cyclic changes don’t directly address rotor RPM and can lead to undesired flight attitudes while the rotor recovers.