AN AIRCRAFT FUEL TANK SYSTEM

The invention refers to an aircraft fuel tank system, comprising at least one aircraft fuel tank (1) having an outer surface (1a) shaped with an aerodynamic profile and comprising a curved lowermost section (1a') holding a volume where fuel can accumulate, the curved lowermost section (1a') having an inner surface (1b'), and the tank (1) further comprising a structure (2) to stiffen said tank (1); and, a filling element (3) mounted on the curved lowermost section (1a') and attached to the structure (2), the filling element (3) having a lower surface (3a) shaped with the inner surface of the curved lowermost section (1b') and an opposite upper surface (3b) configured to fulfill the volume hold by the curved lowermost section (1a') such that a substantially plain low internal surface is defined in the aircraft fuel tank (1) in order to avoid the accumulation of unreachable fuel.