A flat-jet fuel injector for an aircraft turbine engine, comprising a body having a generally elongate shape having a longitudinal axis A, the body comprising a main pipe having a generally elongate shape having a longitudinal axis B substantially perpendicular to the longitudinal axis A, the two longitudinal ends of the main pipe being connected directly and respectively to longitudinal ends of two secondary pipes having a generally elongate shape having a longitudinal axis C at least substantially parallel to the longitudinal axis A, and being configured to form, respectively, two separate fuel flow inlets intended to meet substantially at the middle of the main pipe which comprises at least one ejection slot for ejecting the fuel jet, wherein at least one of the main and secondary pipes defines a flow area, at least one geometric parameter of which, such as the shape or a dimension, varies along the pipe and/or is different from the same geometric parameter defined by a flow area of another of the pipes.