3. B. (7) (e)
Back Course (BC) Mode (See Figure 259, sheet 3.)
The back course mode provides for automatic intercept, capture,
and tracking of the back course localizer signal.
When flying
a back
course localizer approach, glideslope capture is
automatically inhibited.
The back course mode is set up and
flown exactly like a front course localizer approach, with the
following differences:
. On the GP-820 Flight Guidance Controller, the BC button is
selected.
With the aircraft outside the normal localizer capture limits,
the PFD will annunciate:
●
●
At
●
HDG in green.
BC in white.
localizer capture, the PFD will annunciate:
BC in green and is boxed for 5 seconds to emphasize that the
captur~ phase has occurred.
tlhenthe back course mode was selected on the GP-820, logic
in the flight guidance computer was established to internally
reverse the polarity of the course error and localizer signals.
Additionally, a gain change takes place in the computer when
BC is selected, since the aircraft will now be closer to the
localizer transmitter by the length of the runway plus
1000 feet.
At back course capture, the flight guidance computer will
generate a roll command to smoothly capture and track the back
course localizer signal.
In addition, the previous roll mode
is cancelled. To allow initiation or continuation of the mode,
the selected PFD and NAV data must be valid.
(f) Category 2 - Optional
A category 2 approach is flown the same as an ILS approach.
Refer to paragraph 3.B.(7)(d).
(g) Roll Autopilot Mode Flow (See Figure 259, sheet 4.)
The roll autopilot diagram shows two signal paths for the
lateral steering command.
The first path is with the autopilot
disengaged and routes the lateral steering command to the
symbol generator only.
This path is discussed in paragraph
3.B.(7)(g)~. The second path is with the autopilot engaged,
and routes the lateral steering command to both symbol
generators and to the aileron servo drive motor. This path is
discussed in paragraph 3.B.(7)(g)~.
22-14-00
Page 298.95
Aug 15/91
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