Do not operate the rotor brake until both engines are ___________ and the rotor RPM (NR) is below ________%.

• A. Shutting down; 25
• B. Shutting down; 50
• C. Shut down; 60
• D. Shut down; 50

Answer: (D)

The key idea is safe rotor-brake use after shutdown. The rotor brake should be engaged only once the engines are completely off and the rotor speed (NR) has fallen to a low, safe level. Waiting until NR is below 50% means the rotor is slowing down enough that applying the brake won’t impose large braking forces on a still-driven drivetrain or cause undue stress on gears and shafts. If you apply the brake while engines are still running or NR is high, you risk loading or damaging the transmission and rotor system due to sudden braking torque while power is being transmitted. So the best practice is: shut down both engines and ensure NR is under 50% before using the rotor brake.