Abstract: The system according to the invention uses GPS/NAVSTAR navigation satellites and includes:a fixed station located in the vicinity of the landing zone, containing a receiver for positioning by satellite that gives an estimate of the position of this fixed station and computing means that give correction data representing the deviation between this estimate and a reference position; and a data transmitter transmitting, in particular, these correction data on a radio channel which is conventionally used to transmit data in a microwave landing system called the MLS system;an on-board station in each aircraft comprising: an MLS receiver capable of receiving the ancillary data transmitted by the MLS system, a receiver for positioning by satellite and a computing device by which the correction data can be used to correct an estimate of position given by the positioning receiver.