The RM-850 Radio Management Unit (RMU) is the central control unit for the entire radio system. The RM-850 gives complete capability for controlling the operating mode, frequencies, and codes within all the units of the radio system. The RM-850 has the capability to switch its operation from primary radio system to the cross-side system. The RM-850 is a color cathode ray tube (CRT) based controller that can select a function by pushing a line select key adjacent to the parameter to be changed. Any selectable parameter, such as VOR frequency, can be changed by pushing the corresponding line key next to the displayed parameter and then rotating the controller tuning knob. For some functions, additional pushes of the line select key toggles modes or recalls stored numbers. The RM-850 is also the input to the radio system for external FMS tuning. Digital signals from the Flight management system come into the RM-850, where they act in much the same manner as if the front tuning knob were being operated. This allows the Flight management system to enter into the system in an organized manner, and appears to the system as if the flight crew is tuning the receiver. Backup navigation data is provided to the RM-850 via the RSB from both remote NAV units, and/or via RS-422 data buses from whichever remote NAV unit is married to the CDH for emergency backup purposes.

For ease of operation, the RM-850 screen is divided into windows. Each window groups the data associated with a particular function of the radio system. Each window (COM, NAV, ATC, ADF, and TCAS) displays the frequency and/or operating mode of the associated function. The RMU also has other display modes, called pages, which perform additional features and functions for the control of the radio system. Located on the front of the RM-850 is a button labeled PGE. Pushing the PGE button causes the RMU to toggle through different pages of the display. The RM-850 broadcast messages addressed to radio functional modules and receive data from the radios via the RSB. Three major functions of the RMU are to output tuning (channel or frequency) control data, output operational mode control data for the radios, and display the tuned active channel or frequency and operational mode. The measurements for the RM-850 are height 5.06in, width 4.06in, length 11.10in and the weight is 7.2lb. The nominal power is +28V d, 33W and panel lighting 5V ac/dc 0.025W.