1. A method for constructing a flight trajectory of an aircraft, deployed in a flight management system, said flight management system employing means for determining, on the basis of a flight plan advised by the pilot, an objective navigation point sequence (S PNO ), an objective navigation point being characterized at least by a geographical position, and means for determining a flight domain (D V ) consisting of a set of parameters defining the aerodynamic behaviour of the aircraft, the method comprising: computing a sequence of state vectors (E i ) representing the trajectory of the aircraft; the said state vectors (E i ) having as components at least a time (t i ), a geographical position (X i ) of the aircraft and components of a speed vector (V i ) of the aircraft; a state vector (E i+1 ) being determined on the basis of the state vector (E i ) preceding it in the sequence by: computing the components of the speed vector (V i+1 ), including: determining a flight setpoint, by selecting an objective navigation point from the sequence (S PNO ), determining a joining strategy adapted to the flight setpoint and to the flight domain (D V ) by means of a predefined library (L Sr ) of joining strategies, determining a manoeuvre by means of the flight domain (D V ), allowing the aircraft to follow the joining strategy towards the flight setpoint, and computing the other components of the state vector (E i+1 ), on the basis of the components of the speed vector (V i+1 ) and the components of the preceding state vector (E i ).