The VOR/ILS uses radio navigation signals to aid in aircraft navigation and instrument approaches. The system indicates compass bearing of a station and deviation of the aircraft from a selected course (ground station radial). In TACAN mode the ID-351 (CDI) will indicate course deviation from the selected radial. In VOR/LOC mode, the CDI will indicate both lateral deviation from the localizer and vertical deviation from the glidepath when an ILS frequency is selected. When a VOR frequency is selected only lateral deviation from the selected radial will be valid.

When tuned to the appropriate VOR frequency between 108.0 to 117.95 MHz the VOR receiver continuously receives bearing information as determined by measurement of signals transmitted by the ground station. When tuned to the appropriate ILS frequency between 108.1 to 111.95 MHz (odd tenths only) localizer information is displayed on the CDI.