A monitoring device for an augmented satellite-based positioning system which has a reference station with a transmitting device for transmitting a correction signal, wherein the monitoring device is designed for carrying out long-term monitoring of availability and precision of the positioning system for the purpose of air traffic control, said system comprising: - at least one first receiving device, which is designed for reception of at least one satellite signal of the positioning system, - at least one second receiving device, which is designed for reception of the correction signal, - first signal quality determination means, which are designed for determination of a first parameter set (q 1) which characterizes a quality of the correction signal, - first signal quality determination means, which are designed for determination of a second parameter set (q 2) which characterizes a quality of the satellite signal, - position error determination means, which are designed for determination of a position error (p E) of the positioning system, - position uncertainty monitoring means, which are designed for determination of a spatial position uncertainty range (p PL) of the positioning system, - availability determination means, which are designed for determination of a current availability of the positioning system as a function of the first parameter set (q 1), the second parameter set (q 2), the position error (P E) and the spatial position uncertainty range (p PL), and - checking means, which are designed for checking of at least one characteristic value of the positioning system as a function of a position of a satellite of the positioning system which transmits the satellite signal, wherein - the reference station is designed as a stationary ground station, - the correction signal is a correction signal transmitted in the VHF band, - the checking means comprise a first display device for displaying the at least one characteristic value for different positions of the satellite, and - the first display device is configured for generation of a graph which shows the characteristic value as a function of a horizontal angle and of a vertical angle of the position of the satellite relative to a position of the monitoring device, in order to inform air traffic controllers of the current availability of the positioning system. - at least one first receiving device, which is designed for reception of at least one satellite signal of the positioning system, - at least one second receiving device, which is designed for reception of the correction signal, - first signal quality determination means, which are designed for determination of a first parameter set (q 1) which characterizes a quality of the correction signal, - first signal quality determination means, which are designed for determination of a second parameter set (q 2) which characterizes a quality of the satellite signal, - position error determination means, which are designed for determination of a position error (p E) of the positioning system, - position uncertainty monitoring means, which are designed for determination of a spatial position uncertainty range (p PL) of the positioning system, - availability determination means, which are designed for determination of a current availability of the positioning system as a function of the first parameter set (q 1), the second parameter set (q 2), the position error (P E) and the spatial position uncertainty range (p PL), and - checking means, which are designed for checking of at least one characteristic value of the positioning system as a function of a position of a satellite of the positioning system which transmits the satellite signal, - the reference station is designed as a stationary ground station, - the correction signal is a correction signal transmitted in the VHF band, - the checking means comprise a first display device for displaying the at least one characteristic value for different positions of the satellite, and - the first display device is configured for generation of a graph which shows the characteristic value as a function of a horizontal angle and of a vertical angle of the position of the satellite relative to a position of the monitoring device, in order to inform air traffic controllers of the current availability of the positioning system.