During which range of Np% should stabilized ground operation be avoided?

• A. 70 to 90
• B. 62 to 80
• C. 50 to 65
• D. 65 to 75

Answer: (B)

Stabilized ground operations should be avoided in the range of 62 to 80 percent Np because this range can lead to issues with engine performance and operational safety. Specifically, operating within this RPM percentage can cause the engine to encounter instability, which may increase the risk of power loss or other mechanical failures during critical phases of ground operation.

In flight operations, particularly for rotorcraft, maintaining the correct power and RPM levels is essential for ensuring stability and reliability. The specified range closely aligns with thresholds where engine performance can fluctuate, making it less than ideal for safe ground handling and pre-flight checks. Ground operations should ideally take place outside this range to ensure optimal performance and mitigate risks.

Other ranges provided in the options may not encompass the same risks associated with engine instability. Hence, understanding this particular threshold is vital for maintaining proper operational safety protocols during ground operations.