Which statement about the main fuel system is true?

• A. To govern the correct main fuel flow to the combustion section to start and operate from IDLE through MIL power, under all conditions within the envelope.
• B. To regulate hydraulic fluid for flight controls.
• C. To provide coolant for the engine core.
• D. To supply fuel to the auxiliary power unit.

Answer: (A)

The main idea here is that the main fuel system is responsible for delivering and metering the right amount of fuel to the engine’s combustion chamber so the engine can start and run smoothly from idle up through military power, under all the conditions the airplane might encounter. This system uses components like pumps, the engine fuel control unit, and the fuel manifold to regulate pressure and precisely meter fuel based on throttle position, engine speed, and ambient conditions. It ensures a proper fuel-air mix during light-off, transition to stable operation, and continues to supply the engine with accurate fuel flow as power settings change, all while maintaining safe limits.

Hydraulic regulation, cooling, and APU fueling are separate functions. The hydraulic system handles flight-control fluids, the cooling system manages engine core temperatures, and the APU has its own fuel supply arrangement. None of these describe the main fuel system’s role, which is specifically about metering and delivering fuel to the engine across the start and operating range.