The device includes elements of a processing unit which determine a limit trajectory representing a flight trajectory which is compatible with the aircraft performance during the approach and which shows the limits for the flight of the aircraft. For example, a vertical profile and a horizontal trajectory are determined, with the horizontal trajectory being non-linear so that the energy of the aircraft can be sufficiently dissipated before final approach along an approach axis, while also avoiding obstacles. Thus, a flight trajectory is determined even when the aircraft has deviated from a flight plan and approach axis.