Horizontal Situation Indicator - Cessna 172S Nav III Information Manual

SECTION 7 CESSNA
AIRPLANE AND SYSTEMS DESCRIPTION MODEL 172S NAV III
FLIGHT INSTRUMENTS (Continued)
HORIZONTAL SITUATION INDICATOR
The horizontal situation indicator (HSI) is found along the lower
center of the GDU 1040 Primary Flight Display. The heading
indication data is provided by the GRS 77 Attitude and Heading
Reference (AHRS) and GMU 44 Magnetometer units. The HSI
combines a stabilized magnetic direction indicator (compass card)
with selectable navigation deviation indicators for GPS or VHF
navigation. The HSI is conventional in appearance and operation.
Magnetic heading is shown numerically in a window centered above
the heading index (lubber line) at the top of the HSI. Reference
index marks are provided at 45° intervals around the compass card.
A circular segment scale below the heading window at the top of
the HSI shows half and standard rates of turn based on the length
of the magenta turn vector.
The cyan HSI heading reference pointer ("bug") is set using the
HDG knob on the GDU 1040 display. The selected heading is
shown digitally in a window above the upper LH 45° index mark.
The heading window will disappear approximately 3 seconds after
the HDG knob stops turning. The selected heading will provide the
control input to the Bendix/King KAP 140 when the Autopilot is
engaged in HDG mode.
The CDI navigation source shown on the HSI is set using the CDI
softkey to select from GPS, NAV 1 or NAV 2 inputs. The course
reference pointer is set using the CRS knob on the GDU 1040
display. The selected course is shown digitally in a window above
the upper RH 45° index mark. The course window will disappear
approximately 3 seconds after the CRS knob stops turning. The
selected navigation source will provide control input to the
Bendix/King KAP 140 when the autopilot is engaged in NAV, APR
or REV mode and is receiving a navigation signal from the selected
GPS or VHF NAV radios.
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