The AN/ASN-123C Tactical Navigation System (TACNAV) uses Doppler velocities, GHARS headings and true airspeed data to perform deadreckoning navigational computations. The system also receives sensor information which aids tactical planning. The outputs of the system are displayed to the TACCO. Steering information is provided to the pilots and TACCO through the BDHI system. When the Doppler velocity data is valid and its value is reasonable, the TACNAV operates in the Doppler mode. In this mode, true headings from the GHARS and the Doppler heading and drift velocities are processed to update the position of the aircraft on this display. The TACNAV operates in the air data mode whenever the Doppler velocity data is not valid or its value is unreasonable. In this mode, it uses TAS and the last computed wind to update aircraft position.

Significant events can be manually and/or automatically recorded and stored in the TACNAV computer. The event log can be viewed while airborne or it and the last screen displayed can be down-loaded to the RD493-ASM Recorder/Reproducer for postflight viewing. The RD493-ASM can also be used to up-load a screen display.

The system consists of six Weapon Replaceable Assemblies (WRAs). These WRAs are the navigational computer, TACCO control unit, SENSO control unit, digital display indicator and two equipment mounting bases. A relay box mounted on the underside of the SENSO station and a BDHI control in the radio and navigation control panel are also part of the TACNAV.

The TACNAV is protected by one DC and three AC circuit-breakers, marked “AN/ASN-123C” on the radio circuit-breaker panel. The system receives DC power from the primary bus via the No.2 RADIO MASTER switch and AC power from the No.1 generator.