What is the Np percentage range to avoid stabilized ground operations?

The percentage range of Np that indicates the risk of avoiding stabilized ground operations is critical for ensuring safety and operational effectiveness in flight training and actual flight operations. In this context, the correct choice falls into the range of 62 to 80 percent. This range is important because when Np—the power turbine speed—deviates beyond this threshold, it could lead to unstable engine performance, potentially resulting in a hazardous situation during flight operations.

Specifically, staying within the 62 to 80 percent range is essential to maintain the engine's performance on the stable operating curve, which ensures that the aircraft operates efficiently and safely. Operating outside of this range increases the risk of disturbances that could compromise the control and stability of the aircraft, particularly in critical phases of flight.

Understanding these parameters is key for pilots and operational personnel, as adhering to these guidelines helps prevent accidents and enhances the overall safety of flight operations. This range reflects the operational limits that are grounded in extensive testing and operational experience, providing a reliable framework for safe flight conduct.