In gravity refueling, which tank fills first?

In gravity refueling, the Aft Cabin Tank is designed to fill first due to its positioning and the way the fuel system is engineered. When gravity refueling is performed, fuel is introduced into the system from an elevated source, allowing the fuel to flow naturally into the tanks based on gravity. The Aft Cabin Tank is typically located at the highest point in the refueling schema, making it the most accessible tank for the initial flow of fuel.

Due to the layout of the fuel system, as fuel enters the Aft Cabin Tank and fills up, it creates a gravity head that facilitates the flow of fuel to the other tanks. This method ensures that overflow and fuel management are optimized as the system balances itself during the filling process. After the Aft Cabin Tank reaches a predetermined level, then other tanks like the Left Mid Tank and Right Mid Tank will begin to fill, but only after the initial filling of the Aft Cabin Tank has occurred.

This systematic filling order is crucial for ensuring that each tank is filled efficiently and safely, which is essential in gravity refueling operations.