Radio Altitude Comparator - Honeywell SPZ-8000 Maintenance Manual

A miscompare condition occurs when one of the above parameters
deviate greater than the allowed threshold. When a miscompare
is detected, the FGC reversion will be dependent upon whether
the IRS monitor resident in the
AHRS or IRS 3 is
valid.
With
the IRS monitor invalid, all
FD
modes will be dropped, the
AP
and YD will disengage, and the IRS miscompare will be
annunciated. A heading miscompare with the IRS monitor invalid
will cause the aircraft to revert to wings level from
HDG hold
and annunciate the IRS
miscompare.
With the
IRS
monitor valid, a miscompare in the FGC
will cause
the FGC to look at the miscompare discretes from the
IRS
monitor. The IRS monitor compares the parameters listed below
between IRS 1 and IRS 2.
Parameter Allowed Error Threshold
Pitch/Roll 3°
Pitch Rate
Yaw Rate
0.3°/sec +Avg Rate /32
Roll Rate
Normal Accel
Lateral Accel 0.05 g + Avg Delta Accel /32
Fore-Aft Accel
Heading
N/A
A miscompare condition in the IRS monitor occurs whenever the
above parameters deviate greater than the allowed threshold
between the IRS monitor and IRS
1 or the
IRS
monitor and
IRS 2.
The IRS
monitor will set the appropriate discrete to the FGC
(either
IRS 1
miscompare or
IRS 2
miscompare).
The FGC does not use the miscompare discretes from the IRS
monitor until the FGC has detected a miscompare. At that point
the FGC uses the
IRS
monitor as a voter by looking at the
miscompare discretes. The FGC will stop using data from the
IRS with which the IRS monitor has miscompared and EICAS will
annunciate "FGC NOT USING IRS (X)".
3. B. (6) (c) Radio Altitude Comparator
The parameter compared by the
FGC is
shown below.
Parameter Allowed Error Threshold
Radio Alt 5 ft + ALT Avg /8
22-14-00
Page 298.86
Apr 15/93
USe
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