TM 55-1510-220-10
Figure 3-12. Copilot's Horizontal Situation Indicator (331A-8P)
heading, course deviation, and glideslope data. The pilot's
HSI allows the desired course and autopilot input to be set
manually. Each pilot's or copilot's HSI will display front
course localizer sensing, when the front course is selected and
back course is flown. Course deviation data is supplied to the
HSI by the VOR I or VOR 2 systems, the TACAN, or the
INS. Glideslope data is supplied by the VOR I or VOR 2
systems. The HSI displays warning flags when the VOR,
TACAN, or glideslope signals are lost or become unreliable.
b.
Controls/Indicators and Functions, Pilot's HSI.
(1)
Rotating azimuth card. The rotating azimuth
card displays slaved gyro-stabilized magnetic compass
information and is graduated in five-degree increments.
(2)
Heading marker. Indicates heading selected
by HDG knob.
(3)
Lubber line. This pointed fixed index mark
aligns with the aircraft symbol to indicate aircraft magnetic
heading on the compass card.
(4)
Course arrow. Indicates VOR radial course
selected by COURSE knob.
(5)
HEADING flag. Indicates that the heading
information displayed is invalid and should not be used.
(6)
COURSE indicator. Provides a digital
readout of the selected course.
(7)
TO-FROM pointers. Two TO-FROM pointers
are situated 180 degrees apart. The one which is visible
points toward the station along the selected VOR or TACAN
radial, or to the next INS waypoint.
(8)
NAV flag. The NAV flag indicates that the
information derived from the selected navigational beacon is
invalid and should not be used.
Change 2
3-23
