The invention relates to a method of assisting in the navigation of an aircraft comprising a step for updating a flight plan according to a new clearance received on board by a ground/onboard communication system. The clearance comprises an action conditional on the flight plan linked to a floating point of the path defined by an altitude constraint of the aircraft; on receipt of the new clearance, the update is performed directly by means of the FMS linked to the communication system. This is a predictive method.