1. A method for managing a flight of an aircraft flying a trajectory determined from a flight plan and calculated by a flight management system, the trajectory necessitating at least one transition between two different aerodynamic configurations of the aircraft, the method comprising: a step of extraction of performance data of the aircraft from a database, at least one item of performance data being a function of an aerodynamic configuration, a step of 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, the first determination step taking account of a variation of the performance data during the transition, and being selected when the performance data make it possible to calculate the variation, the second determination step considering the transition as immediate and being selected when the performance data do not make it possible to calculate the variation.