A system for navigating an aircraft, comprising a flight planning system configured to prepare a set of at least three different trajectories for a flight from a departure point to a destination point, a flight verification system configured to verify each trajectory of the set of trajectories, an onboard flight management system to be installed at an aircraft and having a storage unit for storing the set of trajectories, wherein the flight management system is configured to select one of the trajectories from the set of trajectories as an active trajectory for a current flight of the aircraft, wherein the flight management system includes a replanning unit configured to change, during the current flight, the active trajectory by selecting a second trajectory from the set of trajectories as the active trajectory for the current flight, such as to continue the current flight based on the second trajectory t.