(8) IAS Indicator. Illuminates when airspeed
hold mode is selected.
(9) AP DISC Indicator. Illuminates when
autopilot is disengaged.
(10) BACK LOC Indicator. Illuminates when
back-course mode is selected.
(11) GS CAP Indicator. Illuminates when
glideslope is captured.
(12) NAV CAP Indicator. VOR-I or VOR-2
selected illuminates when selected radial is captured.
VLF selected illuminates when VLF is coupled to the
h. Autopilot Modes of Operation.
(1) Attitude Mode. The autopilot is in the
attitude mode when the ENG / DIS switch, autopilot
mode selector panel, is in the ENG position and no
mode selector switches (HDG, NAV, etc.), have been
selected. Refer to Figure 3A-19. The autopilot will fly
the aircraft and accept pitch and roll rate commands
from the autopilot pitch-turn panel, Figure 3A-20.
(2) Guidance Mode. When the autopilot is in
the attitude mode and a mode selector switch, HDG,
NAV, etc., is pressed, the autopilot is coupled to the
flight director and accepts steering commands from
the computer. Depending on which mode selector
switch on the autopilot mode selector control panel is
pressed, autopilot operation can be described by the
following sub-guidance modes.
(a) Heading Mode. When the HDG
mode is selected on the autopilot mode selector panel
with the autopilot engaged, the autopilot will fly the
aircraft to the heading, and then maintain the heading
under the heading marker on the pilot's horizontal
(b) Navigation Mode. When the NAV
mode is selected on the autopilot mode selector panel,
the system initially switches to the NAV ARM heading-
hold submode, as shown by illumination of the NAV
ARM and HDG indicators on the autopilot/ flight
director annunciator panel. The autopilot will then
command the aircraft to follow the heading under the
heading marker on the pilot's horizontal situation
indicator, with the heading marker set to produce the
desired VOR or localizer intercept angle. The flight
computer will compute a capture point based on
deviation from desired radio beam, the rate at which
the aircraft is approaching this beam, and the course
intercept angle. When beam capture occurs, the HDG
and NAV ARM indicator lamps on the autopilot/flight
director annunciator panel will extinguish and the NAV
CAP lamp will illuminate. The autopilot will then track
the selected radio course with automatic crosswind
Deviation). The system features linearized VOR
deviation when a VORTAC is being used. A LIN DEV
light on the autopilot annunciator will illuminate to
indicate operation. The lateral deviation bar indicates
the distance in nautical miles from the selected radial
regardless of how close the aircraft is to the ground
station. Linear deviation measures the aircraft's
displacement in nautical miles from the selected
associated with normal VOR navigation. Linear
deviation permits flying parallel to any selected course
by maintaining the appropriate needle deflection on
the horizontal situation indicator. When the LIN DEV
light is on, the flight director system is obtaining
distance data from the DME and bearing from the
VOR-1 receiver. Linear deviation operates only when
DME is on NAV 1 receiver and is displayed on pilot's
indicator only. For en route operation in the NAV
mode, full-scale deflection of the lateral deviation bar
equals 10 miles from the selected radial. For VOR
approach operation, the APPR mode should be
selected. This provides linear deviation with the
sensitivity limits of the computer increased so that full-
scale deflection of the lateral deviation bar equals
1 mile from the selected radial. APPR mode should be
selected when within 10 miles of the final approach fix.
Capture is the same as in the NAV mode.
Failure to select APPR for VORTAC or
VOR/DME instrument approaches when
using linear deviation may result in not
meeting obstruction clearance criteria.
(d) Backcourse Mode. When BACK
LOC mode is selected on the autopilot mode selector
panel, localizer capture is the same as in a front-
course approach in NAV or APPR mode. Glideslope
is inhibited during a backcourse approach. The HSI
must be set to the front-course heading so that lateral
deviation will be directional.
(e) Approach Mode. When APPR mode
is selected on the autopilot mode selector panel,
localizer capture is the same as in the NAV mode but
glideslope arm and capture functions are also
provided. When the APPR mode is selected, the NAV
ARM annunciator lamp will illuminate, indicating that
the system is armed for localizer capture. As the
aircraft approaches the localizer beam, the NAV CAP
annunciator lamp will illuminate. Once the localizer is
being tracked, the GS ARM annunciator lamp will
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