PURPOSE: To improve the safety and reliability of an MLS(microwave landing system) by centralizing monitor means which monitor transmission from different MLS stations in a central station.

CONSTITUTION: Stations Si of all microwave landing systems(MLS) are connected to the central station SC through an optical fiber network FO. The central station SC receives signals through an optical link interface IF and converts it into electric signals. Those signals are transmitted to a monitor device MT, a monitor device Mo for channels and data, and a monitor device ME which monitors an angle function and a level transmitted through an antenna. Results of all tests conducted by those monitor devices are sent out to a command managing circuit CL. The command managing circuit CL is connected to an operator interface IO and the optical link interface IF. Therefore, an MLS signal that a guided aircraft receives is divided by time in the central station SC and regenerated.