BFO-OFF switch - OFF.
Mode selector switch - LOOP.
Loop switch - L or R. Turn left or
right until a null is reached (mini-
mum sound in headsets).
Double needle on RMI (fig. 3-9) -
Read course to station,
The true null and direction to the radio
station may be indicated by either end of
the single needle. This ambiguity must be
solved to determine proper direction to
(4.) Shutdown procedure: Mode selector
switch (ADF control panel, fig. 3-18) - OFF.
3-28. TACAN SYSTEMS.
a. Description. Two Tactical Air Navigation
(TACAN) systems are provided. One is dedicated to
the INS and is used only for position updating, and
provides only DME information to the INS.The
other is used in conjunction with other avionics sys-
tems, including the flight director system and the
autopilot. For normal navigation TACAN is a radio
navigation system which provides aircraft distance
and bearing information relative to a TACAN
ground station. Both systems operate in the L band
frequency range of 962 to 1213 MHz. Their range,
though limited to line-of-sight, is designed to pro-
vide reliable reception of a TACAN ground station
at a distance of 170 nautical miles at an aircraft alti-
tude of 20,000 feet. The normal time required for
the systems to lock on to a selected ground station
signal is three seconds. Both systems are protected
by a 2-ampere circuit breaker, placarded TACAN,
located on the overhead circuit breaker panel (fig.
b. TACAN System (Non-INS dedicated). The
TACAN system (Non-INS dedicated) consists of a
range unit (which includes the system transmitter)
and a bearing unit, both located in the right nose
avionics compartment; a distance indicator (fig.
3-19) located on the instrument panel; a control
unit (fig. 3-20) located in the pedestal extension;
and an antenna, located on the top of the fuselage.
The TACAN system (non INS dedicated) operates
in conjunction with TACAN and VORTAC ground
stations to provide distance, ground speed, time-to-
station, and bearing-to- station data. It operates in
the L band frequency range on one of 252 preselec-
ted frequencies, 126 X mode and 126 Y mode chan-
nels. Course deviation to TACAN stations are dis-
played on the HSIs. Distance, time-to-station, and
ground speed are displayed on the TACAN digital
display (fig. 3-19). The ground speed and time-to-
station are accurate only if the aircraft is flying
directly toward the ground station at a sufficient dis-
tance that the slant range and ground range are
nearly equal. The (Non-INS dedicated) TACAN sys-
tem may be connected to and used with the autopi-
lot system. When employed as the primary means of
navigation, aircraft flight may be controlled manu-
ally or by the autopilot. Indications of aircraft head-
ing and bearing to ground stations are displayed on
the horizontal situation indicators. Magnetic bearing
to a station is displayed by the RMI and pilots HSI
bearing pointer. TACAN distance, ground speed,
and time-to-station are all displayed on the TACAN
indicator located on the copilots instrument panel
(fig. 2-29). TACAN distance is displayed on the
HSIs. The TACAN control panel (fig. 3-20) enables
selection of the TACAN frequency (channel) to be
used, and provides for self-test of TACAN circuits.
At the present time, most TACAN and VORTAC
stations are operated in the X mode. When Y mode
stations are operational, air navigation charts will
designate the Y mode stations. The small (outer)
control provides system power ON-OFF and station
identifier tone, volume and control.
INS TACAN System. The INS TACAN sys-
tem is coupled directly to INS circuits. It is dedi-
cated only to updating the INS, is activated when
the INS is operational, and is controlled only by the
INS. The INS TACAN consists of a range unit and
a distance indicator, both located on the INS equip-
ment rack and both identical to counterparts in the
(non-INS dedicated) TACAN and antenna, located
on the underside of the fuselage (fig. 2-1). No con-
trols are required or provided for the INS TACAN
d. Controls/Indicators and Functions.
(1.) TACAN control panel.
TEST SWITCH. Activates system
CHANNEL INDICATOR. Dis-
plays selected TACAN channel.
X-Y SWITCH. Selects X or Y
mode for TACAN channels.
OUTER CHANNEL SELECTOR
KNOB. For manual selection of
tens and hundreds part of channel
INNER CHANNEL SELECTOR
KNOB. For manual selection of
units part of channel number.