How does an electric auxiliary fuel pump function in an aircraft?

An electric auxiliary fuel pump serves a critical role in an aircraft's fuel system by supplementing the engine-driven fuel pump during specific conditions, particularly during engine starts and in low-pressure situations.

When starting the engine, the auxiliary pump can provide the necessary fuel pressure to ensure the engine's fuel system operates effectively. This is especially important in case the engine-driven pump, which normally operates once the engine is running, has not yet built up sufficient pressure. By providing immediate fuel pressure, the electric pump facilitates smoother engine starts and enhances reliability.

Additionally, in scenarios where the engine-driven pump may not supply adequate fuel pressure—such as during high-demand phases of flight or certain emergency situations—the auxiliary pump can engage to maintain the necessary fuel flow to the engine. This dual function helps to ensure safety and efficiency in aircraft operations.

The other choices do not accurately describe the purpose of the electric auxiliary fuel pump; it does not replace the engine-driven pump entirely, it is not used for regulating airflow to the engine, nor does it function as a backup for the fuel gauge. Understanding this specific role of the auxiliary fuel pump is essential for pilots to ensure they can manage their fuel systems effectively.