TM 55-1510-220-10
Figure 3-18. Tacan Distance Indicator
(a)
Mode selector switch (ADF control panel, fig.
3-17) OFF.
3-27. 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 systems, 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 provide reliable reception of a TACAN ground
station at a distance of 170 nautical miles at an aircraft
altitude of 20,000 feet. The normal time required for the
systems to lock on to a selected ground station signal is three
seconds. The avionics TACAN is protected by a 2-ampere
circuit breaker, placarded TACAN, located on the overhead
circuit breaker panel (fig. 2-27). The INS TACAN is
protected by a 2-ampere circuit breaker, on the INS J-box. I
b.
TACAN System (Avionics). The TACAN system
consists of a range unit (which includes the n system
transmitter) and a bearing unit, both located in the right nose
avionics compartment; a distance indicator (fig. 3-18),
located on the instrument panel; a control unit (fig. 3-19),
located in the pedestal extension; and an antenna, located on
the top of the fuselage. The TACAN system (Avionics)
operates in conjunction with TACAN and VORTAC ground
stations to provide distance, groundspeed and time to-station
data. It operates in the L band frequency range on one of 252
preselected frequencies, 126 X mode and 126 Y mode
channels. Course deviation for TACAN stations is displayed
on the HSI. Distance, time-to-station, and groundspeed are
displayed on the TACAN digital display (fig. 3-18). The
groundspeed and time-to-station are accurate only if the
aircraft is flying directly toward the ground station at a
sufficient distance that the slant range and ground range are
nearly equal. The (Avionics) TA-CAN system may be
operated by the flight director system or connected to and
used with the autopilot
Change 2
3-34
