INSTRUMENT FLIGHT RULES WORKBOOK
information. Like VOR, TACAN provides 360 courses radiating from a station. Distance
measuring equipment, an integral part of TACAN, provides continuous slant-range distance
information. An additional advantage is that TACAN ground equipment is compact and
relatively easy to transport. This provides great versatility in beacon installation and mobility.
Stations that have VOR and TACAN systems collocated are called VORTAC stations.
The TACAN has a three-position switch. The three positions are as follows (Figure 1-9):
T/R Transmit and Receive
The OFF position disconnects the unit from the aircraft power supply. In the STBY position, the
TACAN radio receives magnetic bearing information from ground TACAN navigation facilities.
This information is displayed in the cockpit by the No. 2 needle of the RMI (Figure 1-3). In the
T/R position, the TACAN radio receives magnetic bearing and distance information. The
distance from the aircraft to the TACAN navigation facility is displayed in the cockpit on the
Naval Aircraft Collision Warning System (NACWS). In the T/R position, the TACAN
determines distance by measuring the elapsed time between the transmission of an interrogating
pulse from the airborne set and the reception of the corresponding reply pulse from the ground
Figure 1-9 TACAN/TCN-40 Control Panel
Although a TACAN radio is a transceiver, it cannot be used to transmit or receive voice
communications. A TACAN station will identify itself approximately every 37.5 seconds in
Morse code using its three-letter identifier. The appropriate mixer switch must be ON to hear the
TACAN station passage is indicated by:
Distance (DME) decreases to a minimum (primary indication),
TACAN needle rotates 180º,
INTRODUCTION TO AIRBORNE NAVIGATION AND COMMUNICATIONS
EQUIPMENT AND PRINCIPLES OF OPERATION 1-13
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