Fuel flow to the engine is controlled by which system?

Fuel flow to the engine is controlled by which system?

• A. A mechanical fuel metering system.
• B. The ignition switch position
• C. A manual throttle linkage only.
• D. An electronic control (EFC) working in conjunction with a hydro-mechanical unit (HMU).

Answer: (D)

Fuel flow is controlled by the electronic control unit that commands the hydro-mechanical metering system. The electronic fuel control (EFC) receives signals from the thrust advance (throttle) position and engine sensors, then computes the required fuel flow to achieve the requested thrust. It sends that command to the hydro-mechanical unit (HMU), which physically meters the fuel and regulates pressure to the injectors. This combination provides precise, responsive fuel metering across all flight conditions and protects the engine from malfunctions. The ignition switch only powers systems and does not set fuel flow, and a manual throttle linkage by itself cannot provide the electronic calculation and protection features. A purely mechanical fuel metering system lacks the adaptability and precision of the electronic control working with the HMU.

Fuel flow is controlled by the electronic control unit that commands the hydro-mechanical metering system. The electronic fuel control (EFC) receives signals from the thrust advance (throttle) position and engine sensors, then computes the required fuel flow to achieve the requested thrust. It sends that command to the hydro-mechanical unit (HMU), which physically meters the fuel and regulates pressure to the injectors. This combination provides precise, responsive fuel metering across all flight conditions and protects the engine from malfunctions.

The ignition switch only powers systems and does not set fuel flow, and a manual throttle linkage by itself cannot provide the electronic calculation and protection features. A purely mechanical fuel metering system lacks the adaptability and precision of the electronic control working with the HMU.