How is fuel supplied to the APU?

The correct answer demonstrates the method by which the Auxiliary Power Unit (APU) receives fuel. The APU is designed to operate efficiently by utilizing a gravity-fed fuel system, which allows fuel to flow into it without the need for additional pressure. This system relies on gravity to move the fuel from higher points in the aircraft's fuel tanks to the APU, ensuring a consistent supply of fuel for operation.

Understanding how the APU is supplied fuel is essential to ensure it operates effectively when needed, particularly during ground operations or in the event of primary engine failure. This method also simplifies the fuel delivery system by reducing the necessity for additional pumps and associated components.

Other methods mentioned, such as pressurized fuel lines or separate fuel pumps, are more commonly associated with the main engines of an aircraft, where maintaining fuel pressure is critical. A gravity-fed system, on the other hand, is typically sufficient for the operational requirements of an APU, highlighting its simplicity and reliability.