Honeywell SPZ-8000 Maintenance Manual page 569

With the aircraft outside of the normal capture range of the
VOR
signal (typically the
CDI on the PFD and ND is
greater than
two dots), the pilot selects the LNAV button on the GP-820
Flight Guidance Controller. At this time, the PFD will
annunciate
HDG
in green and VOR in white.
The FZ-820 Flight
Guidance Computer is now armed to capture the VOR
signal and is
generating a roll command to fly the heading select mode as
previously discussed in paragraph 3.B. (7)(a).
When reaching the lateral beam sensor (LBS)
trip point, the
system automatically drops the heading select mode and
switches to the
VOR capture phase. The following is observed
on the PFD:
. The white VOR
annunciator extinguishes.
. The green HDG
annunciator extinguishes.
.
A
green
VOR is
annunciated and is boxed for 5
seconds to
emphasize the capture phase of operation.
The FZ-820 now generates the proper roll command to bank the
aircraft to capture and track the selected VOR radial. When
the course select pointer was set on the ND using the course
knob on the GP-820 Flight Guidance Controller, the course
select error signal was established. This signal represents
the difference between the actual aircraft heading and the
desired aircraft course. The course error signal is then sent
from the DC-884 Display Controller to the symbol generator and
to the FZ-820 through the avionics standard communications bus
(ASCB). Next, the course error signal is TAS (true airspeed)
gain programmed. TAS gain programming of the course error
signal is performed to achieve approximately the same aircraft
response for a given command, regardless of the aircraft's
airspeed and altitude. The TAS computation is derived from
airspeed and barometric altitude information provided from the
AZ-81O Digital Air Data Computer through the ASCB. From the
TAS
gain programmer, the course error signal is summed with
radio deviation.
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.
The lateral gain programming is performed as a function ofDME
distance to the station and barometric altitude. This gain
programming adjusts for the aircraft either coming toward or
moving away from the VOR station. The DME compensation circuit
approximates ground range to the station for more accurate gain
programming and to help calculate over station sensing (0SS).
22-14-00
Page 298,89
Aug 15/91
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