A method is provided for managing the flight of an aircraft flying a trajectory calculated by a flight management system. The trajectory necessitates at least one transition between two different aerodynamic configurations of the aircraft. The method comprises: extraction of performance data of the aircraft from a database, at least one item of performance data being a function of an aerodynamic configuration, selection between a first determination step and a second determination step, a step of determination of a start point and of an end point of the transition between two aerodynamic configurations and engine speeds of an aircraft during a flight, the determination step being implemented by the flight management system and chosen from among the first and second determination steps, the determination step calculating the trajectory by numerical integration of the equations representative of the dynamics of the aircraft making use of the performance data of the aircraft.