An aircraft fuel system having a fuel tank and a baffle dividing the fuel tank into a primary fuel containing space and a secondary fuel containing space. A fuel drain is provided through which fuel flows from the primary fuel containing space into the secondary fuel containing space. A primary fuel outlet draws fuel from the primary fuel containing space and a secondary fuel outlet draws fuel from the secondary fuel containing space, wherein fuel flow through the primary fuel outlet causes fuel flow through the secondary fuel outlet. The mass flow rate of fuel through the fuel drain is restricted so that the allowable mass flow rate of fuel through the secondary fuel outlet is configured to be greater than the allowable mass flow rate of fuel through the fuel drain in the baffle.

A fuel supply system for an aircraft is provided for delivering in use fuel from a fuel tank to an aircraft powerplant. The in use fuel flows along a fuel flow passage from the fuel tank to the powerplant. A downstream pump is associated with the powerplant and configured to draw fluid along the fuel flow path so as to supply it to the powerplant in use. An upstream pump is disposed in or associated with the fuel tank and operable to pump fluid along the fuel flow passage. A pressure sensor is configured to monitor a pressure at an inlet to the downstream pump. A fuel system controller is responsive to the pressure sensor and configured to control the upstream pump so as to maintain the pressure at the inlet to the downstream pump at or above a predetermined threshold pressure.

A fuel supply system for an aircraft is provided for delivering in use fuel from a fuel tank to an aircraft powerplant. The in use fuel flows along a fuel flow passage from the fuel tank to the powerplant. A downstream pump is associated with the powerplant and configured to draw fluid along the fuel flow path so as to supply it to the powerplant in use. An upstream pump is disposed in or associated with the fuel tank and operable to pump fluid along the fuel flow passage. A pressure sensor is configured to monitor a pressure at an inlet to the downstream pump. A fuel system controller is responsive to the pressure sensor and configured to control the upstream pump so as to maintain the pressure at the inlet to the downstream pump at or above a predetermined threshold pressure.