coupled to the flight director and accepts steering commands
from the computer. Depending on which selector switch
(autopilot mode selector control panel, fig. 3-20) is pressed,
autopilot operation can be described by the following
Heading mode. When HDG mode is
selected (autopilot mode selector control panel, fig. 3-20),
with the autopilot engaged, the autopilot will fly the aircraft
to, and then maintain, the heading under the heading marker
on the pilot's HSI.
Navigation mode. When NAV Mode is
selected (fig. 3-20),. the system initially switches to the
NAV ARM heading hold submode, as shown by the
illumination of NAV ARM and HDG indicators (fig. 3-22).
The autopilot will then command the aircraft to follow the
heading under the pilot's HSI (when the heading marker set
to produce the desired VOR, TACAN, INS or localizer
intercept angle). The flight computer will compute a capture
point based on deviation from the desired radio course, the
rate at which the aircraft is approaching this course, and the
course intercept angle. When course capture occurs, the
HDG and NAV ARM annunciators (fig. 3-22) will
extinguish and the NAV CAP annunciator will illuminate.
The autopilot will then track 'the selected radio or INS course
with automatic crosswind correction.
Back-course mode. When B/C mode is
selected on the autopilot mode selector control panel (fig. 3-
20), 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
frontcourse heading so that front course sensing will be
Approach mode. When APPR mode
is selected (autopilot mode selector control panel, fig. :-20),
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 light will illuminate, indicating that the system is
armed for localizer capture. As the aircraft approaches the
localizer beam, the NAV CAP annunciator light will
illuminate. Once the localizer is being tracked, the G(S ARM
annunciator light will illuminate. Glideslope capture is
dependent on localizer capture and must occur after localizer
capture. The localizer is always captured from a
selected heading, but the glideslope may be captured with the
autopilot operating in any vertical mode (pitch hold, altitude
hold, or indicated airspeed hold), and from above (not
recommended), or below the glideslope. At the point of
glideslope intercept, the GS CAP annunciator light will
illuminate and all preselected vertical modes will be cleared.
For localizer capture above the glideslope, NAV should be
engaged until the aircraft has descended to the glideslope.
After descending to the glideslope, APPR mode should be
engaged for a coupled approach.
Go-around mode. Pressing the GO AROUND
button on the outboard side of the left power lever (fig. 2-8)
selects the go-around mode. Go-around mode may be
selected from any lateral mode (HDG, NAV, APPR, or B/C).
When go-around mode is selected: (1) the autopilot is
disengaged, (2) the GA annunciator light will illuminate, and
(3) a command presentation for wings level and 7° nose up
pitch attitude will appear on the pilot's flight director
The heading marker may be preset to
the go-around heading after the
localizer is captured. After go-around
airspeed and power settings are
established, select the HI)G mode to
clear the go-around mode. Pitch
attitude will remain at that used for
go-around until changed with the
PITCH SYNC & CWS button or the
selection of a vertical mode.
Pitch hold mode. The pitch hold mode is
selected by (1) selecting one of the vertical mode selector
switches, or (2) actuating the pitch synchronize and control
wheel steering switch (PITCH SYNC & CWS), located on
each control wheel (fig. 2-17).
Control wheel steering mode. Pressing one of
the PITCH SYNC & CWS switches located on each control
wheel (fig. 2-17) disconnects the autopilot servos from the
control surfaces, and allows the pilot to fly the aircraft to a
new pitch attitude, and synchronizes the horizontal command
bar (pilot's F1)1) to aircraft attitude. The ALT or IAS mode
will disengage (if selected) when the PITCH SYNC & CWS
button is depressed. When the autopilot is coupled to the
HDG, NAV, APPR, or B/C modes, releasing the PITCH
SYNC & CWS switch will cause the autopilot to couple to the
previously selected mode.
Change 2 3-41