Lateral And Vertical Approach Deviation Comparator; Roll Channel Functional Operation - Honeywell SPZ-8000 Maintenance Manual

3. B.
(6) (d)
(7) Roll
(a)
Lateral and Vertical Approach Deviation Comparator
The parameters compared by the FGC are shown below. This
comparator is enabled only if in dual approach mode.
Parameter
Allowed Error Threshold
LOC/AZ Deviation
38 mV (1/2 dot)*
GS/GP Deviation
*Miscompare detected only if opposed polarities and smaller
deviation is more than 10 mV.
Miscompare retained unless
delta between deviations is less than 20 mV.
Channel Functional Operation
Heading Select (HDG) Mode (See Figure 259, sheet 1.)
The heading select mode is used to intercept and maintain a
magnetic heading. Activation of the HDG SEL pushbutton on the
GP-820 Flight Guidance Controller selects the heading select
mode and overrides all roll active F/D modes. The HDG SEL
pushbutton annunciates ON. Selection of heading is made by a
knob on the GP-820 and is displayed on the PFD and also on the
ND if the full compass is displayed. The heading select mode
is annunciated on the PFD by a green HDG.
In the heading select mode, all armed roll F/D modes are
allowed, but the capture of any armed roll mode will override
the heading select mode. To allow initiation and continuation
of the mode, the selected PFD data must be valid and the turn
knob must be in detent.
To operate the mode, the heading bug on the PFD and ND is
positioned around the compass card to the heading the pilot
desires to intercept, using the heading knob on the GP-820
Flight Guidance Controller. The heading select signal from the
GP-820 to the FZ-820 Flight Guidance Computer represents the
desired aircraft heading.
The signal is routed from the
FZ-820 on the ASCB to the SG-884 Symbol Generator. In the
symbol qenerator, the desired aircraft headinq is com~ared
against-actual aircraft heading, and
error signal is routed to the FZ-820
through the ASCB.
In
the flight guidance computer, the
TAS (true airspeed) gain programmed.
performed on the heading error signal to achieve approximately
the same aircraft response, 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.
the resuitant heading
Flight Guidance Computer
heading error signal is
TAS
gain programming is
22-14-00
Page 298.87
Apr 15/93
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