In turboprop operation, which term describes the idle flight condition where RPM is maintained by the propeller system?

• A. Alpha range
• B. Beta range
• C. Idle range
• D. Cruise range

Answer: (A)

In turboprop operation, the propeller is a variable-pitch device controlled by a governor. The alpha range describes the flight regime where, even though the power lever is at a low idle, the propeller RPM is actively maintained by the propeller system through automatic blade-angle adjustments. The governor holds the commanded RPM by changing pitch as loads change, providing a stable, controllable idle and cruise performance without relying on fuel flow alone.

The other ranges serve different purposes: beta range is used for special low-speed or ground operations where the propeller pitch is managed differently (and often used for braking or reverse actions), while cruise range refers to higher RPM where the propeller is still governed but at much higher speeds. Idle range isn’t the term used for this RPM-control mode during flight idle.