If possible, avoid using DME hold or having N/A as a distance display annunciation during VOR
capture and tracking. When in this condition the light control computer cannot use DME distance
for gain programming.
When lying a VOR intercept, the optimum intercept angle is less than 45 degrees. When the aircraft satisies VOR
track conditions, the course error signal is removed from the lateral steering command. This leaves radio deviation,
roll attitude, and lateral acceleration to track the VOR signal, and to compensate for beam standoff in the presence
of a crosswind. The system will automatically compensate for a crosswind of up to 45 degrees course error. As the
aircraft approaches the VOR station, it will enter a zone of unstable radio signals (zone of confusion). This zone
radiates upward from the station in the shape of a truncated cone. In this area, the radio signal becomes highly
erratic and it is desirable to remove it from the roll command. The over station sensor monitors entry into the zone of
confusion and removes radio deviation from the roll command. The system also uses the collocated DME signal (if
available) to adjust tracking gains. When over the VOR station, the system will accept and follow a course change
of up to 30 degrees.
(5) VOR approach mode. The set-up procedure for the VOR approach mode is the same as for VOR
tracking, except the VOR APR pushbutton button-indicator on the mode selector panel is depressed instead of the
NAV button-indicator. ARM will be annunciated by the VOR APR button-indicator on the mode selector panel and
APR will be displayed in white on the PFD. The light control computer will now apply the gains appropriate for a
VOR approach. Upon capture of the selected course, the VOR APP mode selector switch will annunciate capture
(CAP ), and APR will be annunciated on the PFD in green.
(6) TACAN navigation and approach mode. TACAN navigation and approaches are accomplished in
similar manner to VOR navigation and approaches. Prior to engaging the mode, perform the following:
(a) TACAN navigation receiver control panel -- Set desired channel.
(b) INS/TCN pushbutton selector switch (display controller) -- Depress to select TCN.
(c) Course pointer (PFD) -- Set desired course on heading dial.
(d) Heading marker (PFD) -- Set desired intercept heading for selected course.
(e) Flight director mode selector panel -- Select NAV for TACAN navigation or APR for a TACAN
approach. The PFD will annunciate NAV arm and capture when appropriate.
The light control system will perform the capture and tracking as described for VOR navigation and approaches.
(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 used.
Lateral steering command gain is programmed in the INS.
LNAV is annunciated on the PFD.
The INS selects desired track.
When the NAV pushbutton button-indicator on the light director mode selector panel is depressed, LNAV
will annunciate in green on the PFD. The light 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 light director mode selector panel.
Selecting go-around mode - Selecting standby mode.
Selecting an alternate ATT, HDG, or NAV source on the display controller.
(8) Localizer (NAV) mode. The localizer mode provides for automatic intercept, capture, and tracking of a
front course localizer beam. Prior to mode engagement, perform the following:
(a) VHF navigation receiver control panel -- Set desired localizer frequency.
(b) NAV source selector switch (display controller) -- Depress to select LOC1 or LOC2.
(c) Course pointer (PFD) -- Set inbound course on heading dial.