What is the NR Power-Off Minimum percentage limit?

• A. 80%
• B. 85%
• C. 90%
• D. 95%

Answer: (C)

The NR Power-Off Minimum percentage limit is established to ensure safe operation of the aircraft in scenarios where the rotor system is not being powered by the engine. This percentage is essential for maintaining control and managing rotor RPM during critical phases, such as in the event of an engine failure.

A minimum of 90% NR (Rotor RPM) during power-off conditions is critical because it allows for sufficient rotor inertia to assist in maintaining control and stability of the aircraft while executing necessary emergency procedures. At this threshold, the rotor system is effective in generating lift and control authority, which is imperative for a safe landing.

When the rotor RPM drops below this minimum limit, the aircraft may experience undesirable aerodynamic characteristics that could compromise safety and control during a forced landing or other emergency maneuvers. Thus, maintaining 90% NR is pivotal for effective emergency response and ensuring safety in flight operations.