1. The HEADING NO-GO indicator illuminates
when there is a failure with the heading function in the
central repeater system (CRS).
2. The ATTD BEARING NO-GO indicator
illuminates when there is a failure with the attitude
bearing function in the central repeater system.
3. The DIST NO-GO indicator is not used in the
4. The COURSE selector switch selects the
course data for display on the HSI. The course data is
either set by the computer (COMP) or by the pilots
control box (REP PILOT).
5. The HDG switch selects either magnetic
(MAG) or true (TRUE) heading signal inputs to be
displayed on the NAV/COMM HSI.
6. The HDG/ATTD switch selects either INS-1
or INS-2 to be the source for the heading data signal
to be displayed.
7. The BRG 2 selector switch selects the source
for the information to be displayed on the
NAV/COMM HSI bearing pointer 2. The sources
available for selection are VOR-2, VOR-1, TACAN,
ADF, DF, or DA. In the DA position, drift angle
supplied by the Doppler radar or the central computer
The HSI system functions as a selectable display
for the navigational systems on the aircraft.
When the TACAN, VOR-1, or VOR-2 system is
selected, the corresponding system will provide radial
bearing and bearing information, NAV flag, course
deviation, and To-From signals to the HSI. The
bearing signal will position the bearing pointer 1 or
bearing pointer 2, as selected. The radial bearing
information is resolved with the course set by the
COURSE SET knob. The resultant signal is returned
to the TACAN, VOR-1, or VOR-2 to be used to
develop the course deviation and To-From signals.
These signals are returned to the HSI, where the
course deviation signal displaces the course deviation
bar. The To-From signal will drive the To-From
arrow in the proper direction. If the flag input signal
becomes unreliable during a radio navigation mode,
the NAV flag appears on the HSI. When TACAN is
selected, the distance signal from the TACAN will
position the dials of the distance counters to reflect
the distance to or from the TACAN station.
The UHF-DF/OTPI and the ADF systems will
supply bearing information when selected. This
information is routed to either the bearing pointer 1 or
bearing pointer 2, as selected.
Magnetic and true heading information is
supplied to the HSI compass card by the INS-1 and
INS-2, as selected. Magnetic heading is normally
used to position the compass card. When a tactical
mode is selected, magnetic heading information is
switched out of the circuit, and the compass card will
be driven by the true heading information.
The bearing-distance-heading indicator (BDHI)
(fig. 5-5) may be used with the various navigational
systems, and it provides information according to the
mode selected. Some aircraft may have more than
one BDHI, with separate select switches for each
instrument. The distance counter numerals may be in
a vertical row or horizontal, as shown in figure 5-5.
This section will explain the various parts of the
BDHI. Refer to figure 5-5 while reading the following
The lubber index is a fixed reference mark that
allows the operator to read the heading from the
Figure 5-5.-Bearing-distance-heading indicator.