Which combination of conditions fulfills normal rotor brake shutdown requirements?

• A. NR below 40%, 150-180 psi applied, and not less than 12 seconds
• B. NR below 60%, 150-180 psi applied, and not less than 6 seconds
• C. NR below 20%, 100-120 psi applied, and not less than 12 seconds
• D. NR below 50%, 200-240 psi applied, and not less than 18 seconds

Answer: (A)

Normal rotor brake shutdown is about engaging the brake only after the rotor has slowed to a safe speed and then holding it long enough with the proper hydraulic force to secure the rotor during shutdown. When the rotor speed falls below about forty percent NR, applying 150–180 psi ensures the brake clamp is strong enough to seat and hold the rotor without slipping, while not being so high as to cause excessive wear or bind. Keeping the brake applied for at least twelve seconds gives the system and the rotor time to settle, dissipate residual energy, and prevent any motion from restarting or creeping after shutdown.

Other combinations don’t fit because either the rotor is still rotating too fast (higher NR thresholds), the hydraulic pressure is outside the recommended range (too low to embed the brake firmly or too high, increasing wear or risk of binding), or the dwell time is too short or too long for normal, controlled shutdown.