The two sections of the fuel control unit are the manual control and which other control?

• A. Electronic
• B. Pneumatic
• C. Hydro-mechanical
• D. Automatic

Answer: (C)

The fuel control unit meters fuel using two interacting parts: a manual control and a hydro-mechanical control. The manual control is what the operator moves to request more or less fuel. The hydro-mechanical section uses engine hydraulic pressure together with mechanical linkages to regulate the metering valve, so the actual fuel flow tracks the throttle request while also responding to engine speed and air pressure. This combination provides precise, stable metering with built‑in safeguards like overspeed protection and fuel schedule adjustments for different operating conditions. That’s why the second section is described as hydro-mechanical—it blends hydraulic actuation with mechanical control to finely regulate fuel flow.