(d) Heading marker (PFD) -- Set desired intercept heading for course interception.
The PFD will display the relative position of the aircraft to the center of the localizer beam and the desired inbound
course. With the heading marker set, the heading select mode can be used to perform the intercept. Outside the
normal capture range of the localizer signal (between one and two dots on the PFD); depressing the NAV or APR
pushbutton switch on the light director mode selector will cause the PFD to annunciate LOC and GS in white and
HDG in green. The aircraft will then be lying the desired heading intercept and the system will be armed for au-
tomatic localizer and glideslope beam capture. With the aircraft approaching the selected course interception, the
lateral beam sensor (LBS) is monitoring localizer beam deviation, beam rate, and true airspeed. At the computed
time, the LBS will trip and capture the localizer signal. The light control computer will drop the heading select mode
and generate the proper roll command to bank the aircraft toward the localizer beam center. When the LBS trips,
the PFD will display LOC in green. LOC will be enclosed in a white box for 5 seconds. If both radio altitude and
glideslope deviation are valid, distance is calculated using radio altitude and glideslope deviation data. If only radio
altitude is valid, distance is irst estimated for capture. It is assumed that an approach to the runway is being made
without glideslope, and distance is calculated based on radio altitude only. If radio altitude information is not valid,
distance is estimated as a function of glideslope deviation and true airspeed. If neither radio altitude nor glideslope
data is valid, distance is estimated as a function of true airspeed and time.
Cancel the glideslope mode by:
Depressing NAV or APR pushbutton button-indicator on the light director mode selector.
Selecting a VOR frequency on the selected VHF navigation receiver control panel.
Selecting go-around mode.
Selecting standby mode.
Selecting back course mode.
Coupling light control computer to the cross-side PFD.
Selecting an alternate ATT, HDG, or NAV source on the display controller.
When the aircraft satisies the localizer 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 localizer signal, and to
compensate for localizer beam standoff in the presence of a crosswind. The system will automatically compensate
for a crosswind of up to 45 degrees course error.
(9) Back course mode. The back course mode (BC ) provides for automatic intercept, capture, and
tracking of the back course localizer signal. When lying a back course localizer approach, glideslope capture is
automatically inhibited. The back course mode is set up and lown exactly like a front course localizer approach,
with the following differences:
Back course (BC ) is selected on the light director mode selector.
With the aircraft outside the normal back course localizer capture limits, the PFD will annunciate BC in
white and HDG in green.
At back course capture, the PFD will annunciate BC in green (BC will be enclosed in white box for 5
When the back course mode has been selected on the light director mode selector, logic in the light control computer
was established to internally reverse the polarity of the course error and localizer signals, and provide expanded
localizer display on the PFD. Also again, change takes place in the computer when BC has been selected, since the
aircraft is closer to the localizer transmitter by the length of the runway plus 1000 feet. At back course capture, the
light control computer will generate a roll command to capture and track the back course localizer signal.
Cancel the back course mode by:
Depressing the BC pushbutton button-indicator on the light director mode selector
Selecting a VOR frequency on the selected VHF navigation receiver control panel
Selecting go-around mode
Selecting standby mode
Selecting heading mode