3. B. (6) Comparators
The FGC uses dual
sensors and averages the
inputs from each sensor are compared.
(a) DADC Comparator
data.
The nonaveraged
The DADC comparator is not enabled unless at least one TAS
input is greater than 50 kt. The different parameters compared
by the FGC are shown below.
Parameter Allowed Error Threshold
Dynamic Pressure
10 lb/ft2+qAvg/16
True Airspeed 10 kt + TAS Avg/32
Indicated Airspeed
10 kt + IAS Avg/32
Pressure Altitude 100 ft +ALTAvg/256
Mach 0.02 Mach (if both Mach >0.7)
A miscompare condition occurs when one of the above parameters
deviate greater than the allowed threshold. When a miscompare
is detected in cruise modes or approach modes prior to the
approach track, the AP and YD will disengage and the DADC
mismatch will be annunciated on EICAS, however, flight director
modes will be retained. A miscompare in approach track mode,
the flight director mode will remain in approach track (APPT),
however, reversion to constant speed gain programming will
occur in order to retain operational AP and YD.
(b) IRS Comparator
The different parameters compared by the FGC are shown below.
Parameter Allowed Error Threshold
Pitch/Roll
6.
Pitch Rate 0.6°/sec +Avg Rate/16
Yaw Rate 0.6°/sec +Avg Rate/16
Roll Rate
3.0°/sec +Avg Rate /16
Normal Accel 0.2 g +Avg Normal Accel /16
Lateral Accel 0.1 g +Avg Delta Accel /16
Fore-AFT Accel
Heading
6,
MAG Hdg
60
True Hdg
6*
True Track
6“
Gnd Speed
10 kt + Vgnd Avg/32
22-14-00
Page 298.85
Aug 15/91
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