What is the Np percentage range at idle?

The Np percentage range at idle is correctly identified as 46 to 50. At idle power settings, the Np (propeller speed) should fall within this specified range to ensure optimal performance and safety of the aircraft. Operating within this Np range at idle helps maintain proper engine and propeller operation, preventing excessive wear or potential mechanical issues.

If the Np were either too low or too high outside of this range, it could lead to undesirable engine behavior or inefficient fuel usage. Thus, adhering to the specified percentage not only ensures that the aircraft adheres to operating limits but also enhances overall flight safety and reliability.