Honeywell SPZ-8000 Maintenance Manual page 573

The radio deviation signal is routed from the navigation
receiver to the symbol generator on the ARINC 429 bus. From
the symbol generator, the radio deviation signal is routed to
the FZ-820 through the ASCB, where the signal is lateral gain
programmed.
Lateral gain programming is required to adjust the gain applied
to the localizer signal due to the aircraft approaching the
localizer transmitter and beam convergence caused by the
directional qualities of the Iocalizer transmitter. The
lateral gain programmer is controlled by a distance from
transmitter estimator. The distance estimator is actually a
low pass filter and rate limiter with two modes of operation:
A calculated range mode
. An estimated range mode
If both
radio altitude and glideslope deviation are valid, then
distance is calculated using radio altitude and glideslope
deviation data.
If
only
radio altitude is valid, distance is
first estimated for capture and then, when in the final track 2
mode, 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, then distance is
estimated as a function of glideslope deviation and TAS. If
neither radio altitude nor glideslope data is valid, then
distance is estimated as a function of TAS and time.
From the lateral gain programmer, the localizer signal is
filtered, amplified and summed with the course error signal.
The resultant localizer command signal is then course cut
limited. The course cut limiter functions primarily when
approaching localizer beam center at an intercept angle greater
than 45 degrees and at high speed.
The course cut limiter's function is to limit steering commands
to 45 degrees, which forces a flightpath to get onto localizer
beam center sooner. This is done to prevent overshooting
localizer beam center during the capture phase of operation.
Typically, the roll command will make an initial heading
change, then level out and fly toward the beam. At the
computed time, the roll command will initiate a second heading
change to line up on the localizer beam.
When the aircraft meets the LOC track conditions (LOC TRK + BC
TRK CE < 450), the switch opens. This removes course error
from the roll command, leaving radio deviation, roll attitude,
and lateral acceleration to compensate for beam standoff in the
presence of a crosswind.
22-14-00
Page 298.93
Aug 15/91
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