The flight control computer will now apply the gains
appropriate for a VOR approach. Upon capture of the
selected course, the VORAPR mode selector switch will
annunciate capture (CAP), and APR will be annunciated
on the EADI in green.
(6) TACAN navigation and approach mode.
TACAN navigation and approaches is accomplished in a
similar manner to VOR navigation and approaches. Prior
to engaging the mode, perform the following:
TACAN navigation receiver control panel
Set desired channel.
INS/TCN pushbutton selector switch
(display controller) - Depress to select
Course pointer (EHSI) - Set desired
course on heading dial.
Heading marker (EHSI) - Set desired
intercept heading for selected course.
Flight director mode selector panel -
Select NAV for TACAN navigation or
APR for a TACAN approach. The EADI
will annunciate NAV arm and capture
The flight control system will perform the capture and
(7) Inertial navigation system (INS) steering
mode. Operation in the INS steering mode is similar to
operation in the NAV mode, with the following differences:
Instead of using course error and radio deviation from
the symbol generator, a composite lateral steering
command from the INS through the symbol generator is
Lateral steering command gain is programmed in the
LNAV is annunciated on the EADI.
Desired track is selected by the INS
When the NAV pushbutton switch-indicator on the
flight director mode selector panel is depressed, LNAV
will annunciate in green on the EADI. The flight
command computer will use the INS-supplied steering
commands to track the desired course. Bank angle limit
is 22 degrees.
LNAV mode is cancelled by:
Depressing the NAV pushbutton indicator-selector
switch on the flight director mode selector panel.
Selecting go-around mode
Selecting standby mode
Selecting an alternate ATT, HDG, or NAV source on
the display controller.
(8) Preview and transition mode. A preview
course pointer (magenta) is provided to enable the pilot to
preview data prior to its use. The flight control computer
can be commanded to automatically transition from
tracking the INS to tracking one of the short range
navigation (SRN) sources (VOR, localizer, or TACAN).
One use for this feature is to transition from tracking the
INS to an approach using VOR, localizer, or TACAN.
Set-up for preview course pointer mode is as follows:
INS/TACAN pushbutton selector switch
(display controller) - INS.
NAV pushbutton selector switch (flight
director mode selector panel) - Depress
NAV to capture and track INS track.
EADI - Observe that LNAV (green) is
Selection of VIL or TCN on the display
controller after the above three conditions
have been met.
The preview course deviation bar will respond to
VOR, localizer, and TACAN signals as appropriate.
Once the previewed navigation source is valid, if the
approach mode (for localizer, ILS, or TACAN) or VOR
approach mode (for VOR) has been selected on the flight
director mode selector, the appropriate LOC, ILS, or NAV
annunciator will be illuminated on the EADI.
When the flight director determines that the capture
point for the previewed mode has been reached, it will
transition the flight director from LNAV mode to the
capture mode of the previewed navigation source. The
preview course pointer will then be removed and the
standard course pointer will be slewed to the previewed
Since INS and TACAN are selected with the
same display controller pushbutton switch, it is
possible to inadvertently reselect the INS as the
navigation source rather than preview the
TACAN navigation source.
(9) Localizer (NAV) mode. The localizer mode
provides for automatic intercept, capture, and tracking of
engagement, perform the following: