TM 55-1510-215-10
deviation, and selected headings with respect to
deviation is true regardless of distance from the station,
magnetic north.
Deviation displacement is always
therefore depicting linear instead of angular deviation.
angular. Any warning flag in view indicates that portion
The aircraft symbol pictorially shows actual aircraft
of the HSI display is unreliable. The rotating heading
position in relation to this selected course.
dial is driven by the copilot's compass system.
(I) VOR/ADF switch. Selects NAV 1
b. Controls and Functions
VOR or ADF bearing information to be displayed by the
green VOR/ADF bearing bug.
(1) Lubber line. Fixed heading mark.
(m) Heading knob. Positions the orange
(2) HDG warning flag.
Indicates loss of
heading bug.
reliable heading information.
(n) Symbolic aircraft.
The fixed
(3) Course pointer. The yellow course pointer
miniature aircraft symbol corresponds to the longitudinal
is positioned on the heading dial by the course knob to
axis of the aircraft and lubber line mark. The symbol
select a magnetic bearing that coincides with the desired
shows aircraft position and heading with respect to the
VOR radial or localizer course.
rotating heading dial, and aircraft position in relation to a
radio course.
(4) To-from pointer. The to-from pointers,
(o) Course knob. Positions the yellow
aligned on the course pointer, are located 180 degrees
course pointer.
apart. One always points in the direction of the station.
(p) Glide slope deviation pointer/scale.
(5) Heading select knob.
Positions the
The glide slope pointer displays glide slope deviation.
orange heading bug.
The pointer is in view only when tuned to a localizer
frequency. If the aircraft is below glide slope path, the
(6) Rotating heading dial.
Displays gyro
pointer is displayed upward on the scale. Each dot on
stabilized magnetic compass information. The heading
the scale represents approximately 0.4 degrees
dial rotates with the aircraft throughout 360 . The
displacement.
copilot's compass system provides power to drive the
(q) To-from pointer.
The to-from
rotating heading dial.
pointers aligned on the course pointer, are located 180
(7) Course select knob. Positions the yellow
degrees apart. One always points in the direction of the
course pointer.
station, along the selected VOR, TACAN, or RNAV
waypoint radial.
(8) Course deviation bar and scale. The
(r) Rotating heading dial.
Displays
yellow course deviation bar represents the centerline of
gyro stabilized magnetic compass information. The
selected VOR or localizer courses. The symbolic aircraft
heading dial rotates with the aircraft throughout 360
pictorially shows the actual aircraft position in relation to
degrees. The rotating heading dial is driven by the
this selected course. In VOR operation, each dot
pilot's compass system.
represents 2-degree deviation from the centerline,
(s) Navigation flag.
When the
whereas 5 dots represent 10-degree deviation off
navigation flag is in view, the NAV portion of the system
course. In ILS operation, each dot represents 1/2-
is not valid.
degree deviation from the centerline, whereas 5 dots
(t) Course pointer. The yellow course
represent 2 1/2-degree deviation off course.
pointer is positioned on the heading dial by the course
(9) Symbolic aircraft. The fixed miniature
knob, to a magnetic bearing that coincides with the
aircraft symbol corresponds to the longitudinal axis of
selected course being flown. The course pointer is also
the aircraft and lubber line markings. The symbol shows
positioned by RNAV, or flight director system modes of
the aircraft position and heading with respect to a radio
operation. The course pointer rotates with the heading
course and the rotating heading dial.
dial to provide a continuous readout of course error to
(10) Glide slope pointer and scale. The dual
the computer.
glide slope displays glide slope deviation. The pointer is
3-17. Copilot's Horizontal Situation Indicator.
in view only when tuned to and receiving a localizer
frequency. If the aircraft is below glide slope, the pointer
a. Description. The copilot's horizontal situation
is displayed upward on the scale. Each increment on
the scale indicates an approximate 0.4 degree deviation
indicator (HSI) (fig. 3-9) operates independently from
from the glide slope.
the pilot's. It combines numerous displays to provide a
presentation of the aircraft position. The indicator
displays aircraft displacement relative to VOR or
localizer course, VOR/ localizer deviation, glide slope
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