An aircraft fuel tank system (100, 200) comprising: a series of multiple fuel tanks (102, 202); and intercommunication conduit assemblies (104, 204) fluid-connecting pairs of adjacent fuel tanks (102, 202) in the series to establish a cascade mode of fuel flow serially from one tank to another tank in the series of multiple fuel tanks (102, 202), characterized in that the intercommunication conduit assemblies (104, 204) comprise: an external manifold conduit (104-1, 204-1) spanning a distance between an adjacent pair of the fuel tanks (102, 202), an inlet conduit (104-2, 204-2) connected to one end of the manifold conduit (104-1, 204-1) and extending within an interior of a first tank of the adjacent pair, and a discharge conduit (104-3, 204-3) connected to an opposite end of the manifold conduit (104-1, 204-1) and extending within an interior of a second tank of the adjacent pair; wherein an open terminal end of the inlet conduit (104-2, 204-2) is separated from a top wall (102-1, 202-1) of the first tank by a predetermined distance to establish ullage volume within the first tank; wherein the predetermined distance in one of the fuel tanks (102, 202) in the series is different than the predetermined distance in other fuel tanks (102, 202) in the series. a series of multiple fuel tanks (102, 202); and intercommunication conduit assemblies (104, 204) fluid-connecting pairs of adjacent fuel tanks (102, 202) in the series to establish a cascade mode of fuel flow serially from one tank to another tank in the series of multiple fuel tanks (102, 202), characterized in that the intercommunication conduit assemblies (104, 204) comprise: an external manifold conduit (104-1, 204-1) spanning a distance between an adjacent pair of the fuel tanks (102, 202), an inlet conduit (104-2, 204-2) connected to one end of the manifold conduit (104-1, 204-1) and extending within an interior of a first tank of the adjacent pair, and a discharge conduit (104-3, 204-3) connected to an opposite end of the manifold conduit (104-1, 204-1) and extending within an interior of a second tank of the adjacent pair; wherein an open terminal end of the inlet conduit (104-2, 204-2) is separated from a top wall (102-1, 202-1) of the first tank by a predetermined distance to establish ullage volume within the first tank; wherein the predetermined distance in one of the fuel tanks (102, 202) in the series is different than the predetermined distance in other fuel tanks (102, 202) in the series. an external manifold conduit (104-1, 204-1) spanning a distance between an adjacent pair of the fuel tanks (102, 202), an inlet conduit (104-2, 204-2) connected to one end of the manifold conduit (104-1, 204-1) and extending within an interior of a first tank of the adjacent pair, and a discharge conduit (104-3, 204-3) connected to an opposite end of the manifold conduit (104-1, 204-1) and extending within an interior of a second tank of the adjacent pair; wherein an open terminal end of the inlet conduit (104-2, 204-2) is separated from a top wall (102-1, 202-1) of the first tank by a predetermined distance to establish ullage volume within the first tank; wherein the predetermined distance in one of the fuel tanks (102, 202) in the series is different than the predetermined distance in other fuel tanks (102, 202) in the series.