Flight management system for an aircraft

A flight management system for an aircraft, comprising:

• a critical first avionics module for trajectory calculation, i.e. a module the integrity level and availability level of which are specified by regulatory standards in force, comprising at least one critical avionics computer and/or at least one critical avionics software package for calculating and delivering as output a safe trajectory, based on a flight plan;
• a second module for trajectory calculation that is less critical than the critical first module, i.e. a module the integrity level and availability level of which are lower than those of the first module, comprising at least one computer that is less critical than a computer of the first module, and/or at least one software package that is less critical than a software package of the first module, and that have/has a higher performance than the avionics computers and software packages of the critical first avionics module for trajectory calculation, to calculate and deliver as output an improved trajectory that is less safe than the trajectory delivered by the critical first avionics module, based on a flight plan;
• a critical avionics module for trajectory verification configured to validate or invalidate the safety of the less safe improved trajectory delivered by the second module;
• and
• a critical avionics module for decision-making configured to select a trajectory from the safe trajectory delivered by the critical first avionics module and the less safe trajectory delivered by the second module, so as to select the less safe improved trajectory if its safety is validated by the critical verification avionics module, to select the safe trajectory if the safety of the less safe improved trajectory is invalidated by the critical verification avionics module, and to deliver as output the selected trajectory;
• the critical avionics module for trajectory verification being configured to validate or invalidate the safety of the less safe improved trajectory based on verifications:
• of compliance with the flight plan of the aircraft by the less safe improved trajectory;
• and/or
• of the continuity of the less safe improved trajectory;
• and/or
• of compliance of the performance of the aircraft with the less safe improved trajectory;
• and/or
• of avoidance of obstacles by the less safe improved trajectory;
• and/or
• of a proximity of the start of the less safe improved trajectory to the current position of the aircraft.