A system for piloting an aircraft, at least for piloting the aircraft during an autonomous approach for the purpose of landing, said piloting system comprising at least: - information sources which provide at least one position indication relating to the actual three-dimensional position of the aircraft and information making it possible to characterize a virtual approach axis; and - processing means which process information arising from said information sources, which are capable of determining deviations between the actual position of the aircraft and the position that it would have if it were on said virtual approach axis, and which use the results of these processings, said information sources comprising: - a flight management computer which is associated with a database containing at least said information making it possible to characterize said virtual approach axis; - a positioning system making it possible to determine the actual three-dimensional position of the aircraft, solely with the aid of onboard means, said processing means form part of a flight guidance computer which comprises: - a first calculation means for directly calculating with the aid of said position indication and of said information characterizing the virtual approach axis, linear deviations between the actual position of the aircraft and said virtual approach axis; - a second calculation means for directly calculating with the aid of said position indication and of said information characterizing the virtual approach axis, lateral and vertical angular deviations between the actual position of the aircraft and the position that it would have if it were on said virtual approach axis, said lateral and vertical angular deviations being used by auxiliary means (20, 21) which are connected to said flight guidance computer; and - a third calculation means for calculating, with the aid of the linear deviations calculated by said first calculation means, aircraft piloting setpoints, said auxiliary means corresponding to: - a display and control system which displays said angular deviations on at least one screen of the flight deck of the aircraft; - a warning and surveillance system which uses these deviations to carry out standard surveillance. - information sources which provide at least one position indication relating to the actual three-dimensional position of the aircraft and information making it possible to characterize a virtual approach axis; and - processing means which process information arising from said information sources, which are capable of determining deviations between the actual position of the aircraft and the position that it would have if it were on said virtual approach axis, and which use the results of these processings, - a flight management computer which is associated with a database containing at least said information making it possible to characterize said virtual approach axis; - a positioning system making it possible to determine the actual three-dimensional position of the aircraft, solely with the aid of onboard means, - a first calculation means for directly calculating with the aid of said position indication and of said information characterizing the virtual approach axis, linear deviations between the actual position of the aircraft and said virtual approach axis; - a second calculation means for directly calculating with the aid of said position indication and of said information characterizing the virtual approach axis, lateral and vertical angular deviations between the actual position of the aircraft and the position that it would have if it were on said virtual approach axis, said lateral and vertical angular deviations being used by auxiliary means (20, 21) which are connected to said flight guidance computer; and - a third calculation means for calculating, with the aid of the linear deviations calculated by said first calculation means, aircraft piloting setpoints, - a display and control system which displays said angular deviations on at least one screen of the flight deck of the aircraft; - a warning and surveillance system which uses these deviations to carry out standard surveillance.