Which fuel tank is normally used to supply the APU?

The A320 normally uses fuel from the left wing tank to supply the Auxiliary Power Unit (APU). This is due to the design and fuel distribution system of the aircraft, which is optimized for efficient fuel management and operational safety.

The left wing tank is typically the primary source for the APU because it allows for a more straightforward routing of fuel lines and minimizes the need for complex plumbing that could add unnecessary weight and inertia to the system. This design choice helps ensure that the APU can draw fuel reliably to function properly during ground operations or when engine start-up is required.

Fuel from the center tank is usually reserved for the engines and is used to balance the aircraft's weight. The right wing tank serves similar functions to the left wing tank but is not designated for APU supply under normal operating circumstances. The auxiliary tank is not applicable in this context as well, as it pertains to additional fuel capacities and does not play a role in APU operations on the A320.