Aircraft mission calculation system includes a first calculator configured to calculate a plurality of iso-displacement curves from a selected point, at a displacement range corresponding to several successive displacement increments of the aircraft from the selected point, the iso-displacement curves being obtained at the displacement range for a displacement of the aircraft to a given flight level from displacements of the aircraft at distinct flight altitude levels. The first calculator is configured to determine, based on iso-displacement curves up to the given flight level, obtained at distinct flight altitude levels, taken at the same displacement range of the aircraft, an extended iso-displacement curve at the given flight level maximizing the displacement of the aircraft from the geographical point of origin or minimizing the displacement of the aircraft toward the geographical destination point.