How is RPM controlled on a turboprop aircraft?

• A. The turbo-propeller assembly together with the control assembly maintains a constant RPM of the engine at flight idle (alpha range).
• B. Throttle position directly sets RPM.
• C. RPM is controlled by Fuel metering alone.
• D. RPM is fixed and cannot be changed.

Answer: (A)

In a turboprop, the speed of the propeller (its RPM) is kept constant by a constant‑speed propeller system powered by a propeller governor. The governor continually senses the propeller RPM and, through hydraulic oil pressure, moves the blade angles to maintain the selected RPM. The control linkage from the cockpit provides the commanded setting, and at flight idle (the alpha range) the governor works to hold a steady propeller RPM despite changes in engine load or air conditions.

The throttle mainly governs fuel flow and turbine speed, setting the overall power available, but it is the propeller governor that adjusts blade pitch to hold the RPM steady. So RPM isn’t directly set by throttle position or by fuel metering alone, and it isn’t fixed; it’s actively controlled to stay constant by the propeller/ governor system, especially important at idle to keep smooth operation.