What is the function of the fuel boost pump?

The function of the fuel boost pump is to provide a critical support role during the engine start process. Specifically, it helps to ensure that the fuel system maintains adequate pressure and flow to the engine at the time when it is most needed. During starting, the main ejectors may not be able to deliver sufficient fuel pressure due to the engine not yet being at operational speed, which is where the boost pump steps in. It provides the necessary pressure to overcome any resistance in the fuel lines and allows fuel to flow into the engine. This feature is vital to ensure a successful ignition and stable engine operation as the aircraft transitions from ground to airborne conditions.

The other aspects mentioned in the choices highlight different roles the fuel system can play, but they do not accurately reflect the primary role of the fuel boost pump in the engine start sequence, thereby clarifying why the focus is primarily on its supportive function during that critical phase.