visual indication of the navigational situation of
For detailed operation of the horizontal
situation indicator system, refer to the applicable
the aircraft. The horizontal situation indicator
maintenance instructions manual.
It provides a visual presentation of the horizon-
tal or plane view of the aircraft relative to the
navigation situation. It also provides an integrated
display of navigation data from various sources.
The BDHI is used with various navigation
It presents this data to the pilot in a symbolic
systems and provides information according to
pictorial display for quick and easy assimilation.
the mode selected. Some aircraft have more than
The center portion of the display contains an
azimuth or compass card (callout 6). The card
one BDHI, with separate select switches for each
instrument. The distance counter numerals may
displays aircraft magnetic heading when read
be in a vertical row or horizontal, as the
against the top of the lubber line (callout 8). You
may also read the bearing pointer (callout 7),
course pointer (callout 10), and command heading
The lubber index is a fixed reference mark at
marker (callout 9) against the card.
the top of the instrument face. The compass card
The bearing pointer (outer pointer, shown at
(read under the lubber index) shows the aircraft
2200, provides pictorial bearing information to
heading (either true or magnetic, depending on
the mode used). Two pointers, a single bar and
a ground electronic station. It can also provide
a double bar, can indicate the following:
a bearing to a base or target (as computed by the
navigational computer set). The course pointer
Bearing to a ground electronic station
(inside compass card, at 3000, shows the selected
course to a ground electronic station, or aircraft
Bearing to destination
magnetic ground track. The course deviation bar
(callout 5) (center segment of this pointer) shows
Aircraft ground track
the aircraft's deviation from a selected course. It
Aircraft drift angle
shows this pictorially with respect to the stationary
miniature aircraft symbol (callout 4) at the center
of the display.
The BDHI select switch selects the available
A to-from pointer (callout 11) (just above the
aircraft symbol) shows if the selected course leads
to or from a ground electronic station. A
command heading marker (callout 9) just outside
the compass card (shown at 3000, shows the
command magnetic heading. It also shows, by its
angular displacement from the lubber line, the
heading error angle. The course pointer and the
command heading marker may be set manually
by means of the COURSE SET (callout 12) and
HEADING SET (callout 2) knobs. They can also
be set remotely by external signals to the HSI
course command and heading command servos.
The selected course to a ground electronic station
or aircraft magnetic ground track is also indicated
on the course counter (callout 13). A distance
counter (callout 1) at the lower left shows the
distance in nautical miles. The distance may be
to the ground electronic station, base, or target
(as computed by the navigational computer set).
There are four mode-of-operation lights
(callout 3) (TAC, UHF, MAN, NAV) that show
around the display. They illuminate internally
to show the selected operating modes. The
unilluminated words remain practically invisible.
Figure 7-19.-Bearing-distance-heading indicator.
The instrument uses integral lighting.