According to operational limits, stabilized ground operations should be avoided at Np percentages between?

The correct answer reflects the operational guidelines for the T-6A, which state that stabilized ground operations should be avoided at Np percentages between 62 to 80. Within this range, the risk of encountering undesirable engine performance characteristics can increase. Specifically, these Np percentages correspond to download conditions where the engine may exhibit fluctuations and vibration that could lead to potential mechanical issues if maintained for extended periods.

Maintaining ground operations outside of this range helps ensure engine reliability and safety, preventing excessive stress on critical components. Recognizing this operational limit aids pilots in making informed decisions during ground operations, enhancing overall flight safety. The other options indicate ranges that do not adhere to these established guidelines, thus increasing the likelihood of adverse effects during ground operations.