TM 55-1510-222-10
Figure 3-19. Flight Director Mode Selector (MS-400)
of a loss of valid signal from the gyro or compass, the
command cue on the ADI is biased out of view.
(2) Navigation Mode Switch (NAV). When
depressed,
selects
the
navigation
mode.
The
Navigation Mode represents a family of modes for
various navigation systems including VOR, Localizer,
TACAN and INS.
(3) VOR Mode. The VOR Mode is selected by
selecting either NAV 1 or NAV 2 on the Course
Indicator select switch on the pilot's instrument panel,
and then depressing the NAV button on mode selector
with the navigation receiver tuned to a VOR frequency.
(A VOR indicator, NV1 or NV2 on the pilot's HSI, will
illuminate. VOR NAV information will display on the
pilot's HSI and RMI). Prior to VOR capture, the
command cue receives a heading select command as
described above and the HDG mode switch is
illuminated along with the NAV ARM annunciators.
Upon VOR capture, the system automatically: switches
to the VOR mode; HDG and NAV ARM annunciators
extinguish; and NAV capture (NAV CAP) annunciators
will illuminate. At capture, a command is generated to
capture and track the VOR radial. The course error
signal is gain programmed as a function of airspeed.
Crosswind washout is included which maintains the
aircraft on radial center in the presence of crosswind.
The intercept angle is used in determining the capture
point to ensure smooth and comfortable performance
during bracketing.
When passing over the station, an overstation
sensor detects station passage, removing the VOR
deviation signal from the command until it is no longer
erratic. While over the station, course changes may be
made by selecting a new course on the HSI.
If the NAV receiver is not valid prior to the
capture point, the lateral radial sensor will not trip and
the system will remain in the HDG mode. After capture,
if the NAV receiver, compass data or vertical gyro
become invalid, the ADI command cue will bias out of
view. Also, the NAV CAP annunciators will extinguish if
the NAV receiver becomes invalid.
(4) VOR Approach Mode. The VOR Approach
Mode is selected by depressing the APR button on the
mode selector with the navigation receiver tuned to a
VOR frequency. The mode operates identically to the
VOR mode with the gains optimized for a VOR
approach.
3-36
