An aircraft mission calculation system, comprising a calculation engine for calculating an aircraft path during the mission, comprising: - a first path calculating module, capable of calculating an optimal mission path between a geographical point of origin and a geographical destination point as a function of airplane performance, operational mission specifications and a weather context, preferably evolutive, in a mission space between the geographical point of origin and the geographical destination point, characterized in that the first path calculating module is able to calculate the optimal mission path in a manner non constrained by an array of waypoints and/or paths imposed between the waypoints, the first path calculating module being capable of calculating the optimal mission path as if the aircraft was able to perform a free flight taking account of mission specifications, without accounting for a network of waypoints and/or imposed paths between the waypoints; the calculating engine including: - a module for defining, around the optimal mission path, an optimization region of the path; and - a second path calculating module, able to calculate an optimized path of the aircraft in the optimization region in a manner constrained by a network of waypoints and/or imposed paths between the waypoints, taking the weather context into account. - a first path calculating module, capable of calculating an optimal mission path between a geographical point of origin and a geographical destination point as a function of airplane performance, operational mission specifications and a weather context, preferably evolutive, in a mission space between the geographical point of origin and the geographical destination point, characterized in that the first path calculating module is able to calculate the optimal mission path in a manner non constrained by an array of waypoints and/or paths imposed between the waypoints, the first path calculating module being capable of calculating the optimal mission path as if the aircraft was able to perform a free flight taking account of mission specifications, without accounting for a network of waypoints and/or imposed paths between the waypoints; the calculating engine including: - a module for defining, around the optimal mission path, an optimization region of the path; and - a second path calculating module, able to calculate an optimized path of the aircraft in the optimization region in a manner constrained by a network of waypoints and/or imposed paths between the waypoints, taking the weather context into account. characterized in that the first path calculating module is able to calculate the optimal mission path in a manner non constrained by an array of waypoints and/or paths imposed between the waypoints, the first path calculating module being capable of calculating the optimal mission path as if the aircraft was able to perform a free flight taking account of mission specifications, without accounting for a network of waypoints and/or imposed paths between the waypoints; the calculating engine including: - a module for defining, around the optimal mission path, an optimization region of the path; and - a second path calculating module, able to calculate an optimized path of the aircraft in the optimization region in a manner constrained by a network of waypoints and/or imposed paths between the waypoints, taking the weather context into account. - a module for defining, around the optimal mission path, an optimization region of the path; and - a second path calculating module, able to calculate an optimized path of the aircraft in the optimization region in a manner constrained by a network of waypoints and/or imposed paths between the waypoints, taking the weather context into account.