TACAN (Tactical Air Navigation) SYSTEM

The tacan system functions to give precise air-to-ground bearing and 
distance information at ranges up to approximately 300 miles (depending
on aircraft altitude) from an associated ground or shipboard transmitting
station.  It determines the identity of the transmitting station and
indicates the dependability of the transmitted signal.

When operating in conjunction with aircraft having air-to-air capability,
the A/A mode provides line of sight distance between two aircraft
operating their tacan sets 63 channels apart.  Up to five aircraft can
determine line of sight distance from a sixth lead aircraft in the A/A
mode, provided their tacan sets are set 63 channels apart from the lead
aircraft.  The limit of operation is four times the distance between
the lead aircraft and the nearest aircraft.  The lead aircraft will indicate
distance from one of the other five, but it cannot readily determine which
one.  Before operating in the A/A mode, the frequencies used by each aircraft
must be coordinated.  Tacan information except in A/A mode is presented on
the horizontal situation indicator (HSI), the attitude director indicator (ADI),
and the head-up display.  In A/A mode, both distance and bearing are received
if cooperating aircraft (such as refueling tanker aircraft) have bearing 
transmission capability.

TACAN CONTROLS

The controls for tacan operation are on the ILS/tacan control panel on the
left console, on the steering mode panel on the main instrument panel, and
on the HSI.  The controls on the ILS/tacan control panel are the function
selector knob, the volume control knob, the channel selector knob and the
XY switch.  The controls on the steering mode panel consist of the
steering mode knob.  The controls on the HSI are the course set and the
heading set knob.

Function Selector Knob

The function selector knob is a three-position rotary knob used for selecting
tacan modes of operation.  The mode positions are marked A/A, T/R and REC.

T/R	Tacan receives bearing signals from the tacan ground station,
	and in addition, the tacan interrogates the tacan ground
	station to establish distance from the aircraft to the
	ground station.  The bearing and distance information is 
	displayed on the HSI.

REC	Tacan receives bearing signals from the tacan ground station
	for bearing display on the HSI, and also for steering display
	on the ADI and HUD.  Tacan distance readout is shuttered on 
 	the HSI.

A/A	Tacan interrogates other aircraft which contain a tacan in
	the A/A mode and is tuned 63 channels apart from the 
	channel setting of the interrogating aircraft.  Bearing and
	distance information is received from a cooperating aircraft
	if it has bearing transmission capability.  If the cooperating
	aircraft is not equipped with bearing transmission equipment,
	only distance information is received and the HSI No. 1
	bearing pointer will rotate clockwise at 30 degrees per second.

Volume
Control Knob
	The volume control knob is used to turn the tacan on and off and
	for volume adjustment of the station identity tone signal.

Channel Selector Knob
	The channel select or knob provides for selection of 126 tacan 
	channels.  The control consists of an outer knob used to select
	the units digit of the channel counter (0 to 9) and an inner knob
	used to select the tens and hundreds digits (00 to 12).

XY Switch
	The XY swithc is a toggle-type with positions of X and Y.  Placing
	the switch to the X position provides capability for 126 channel
	operation.  Placing the switch to the Y position adds an additional
	126 channel capability to the tacan system.

Operational information on this page taken from TO 1F-15A-1, Change 1 - 15
August 1984