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than the vertical, and the ground speed less than 50 knots. All data with SPIN mode activated are
automatically recorded. A DFIRS DWNLD option is available on the Engine display with WonW.
Selecting this option downloads the DFIRS data to the MU for easier retrieval.
2.21.3 Avionics BIT. In most instances, two types of BIT are mechanized, periodic and initiated.
Periodic BIT begins functioning at equipment power application. It provides a failure detection
capability that is somewhat less than that provided by initiated BIT in that it does not interfere with
normal equipment operation.
Two forms of BIT derived data are supplied to the MC. One form is validity information associated
with selected data. The second form is equipment failure information which identifies failed
assemblies. The MC uses these two forms of BIT data to implement reversion operation and advisories
for the aircrew as well as equipment status displays for both the aircrew and maintenance personnel.
2.21.3.1 Reversion. When the BIT equipment determines that a function has exceeded a predetermined
threshold, the data derived from that function is immediately indicated as not valid. The MC,
upon receiving this indication, reverts to the next best available source. This source is, in many cases,
Figure 2-50. Flight Aids Reversion Mechanization
A1-F18EA-NFM-000
I-2-159 ORIGINAL
as accurate as the original source. This reversion is maintained as long as the data remains invalid from
the primary source.
Figure 2-50 illustrates this concept for the flight aids. For each unit in the primary path, there is at
least one alternate source of data for reversion. The aircrew is provided appropriate display cueing only
when a reversion results in some loss of capability or performance. If the ALT switch is in RDR and
the radar altimeter fails, the MC removes the displayed radar altitude, replaces it with barometric
altitude, and replaces the ²R² cue with a flashing ²B² cue. If altitude is lost from the FCC and the
altitude switch is in BARO, the MC removes the displayed altitude from the HUD. These examples
illustrate three forms of degraded mode advisories: (1) reversion to an alternate data source of
equivalent accuracy with no cueing; (2) reversion to an alternate data source of lesser accuracy with
cueing; (3) and removal of displayed data when no acceptable alternate source is available. Refer to
Part VIII for further discussion on weapon system reversions.
2.21.3.2 Equipment Status Displays. Equipment status displays (BIT, caution, and advisory)
provide the aircrew with continuous status of the avionics equipment and weapons. A cue to check
equipment BIT status is the appearance of the BIT advisory display on the caution/advisory. The
display is normally on the left DDI. A MENU selectable top level BIT format displays the status of
failed, NOT RDY, or OFF systems of all avionics equipment that interface with the MC. When the BIT
control display is selected on another display, the BIT advisory is removed until another BIT failure
occurs. Messages displayed as a function of equipment status are listed in figure 2-51.
STATUS
MESSAGE
APPLICABLE SYSTEM MESSAGE DEFINITION
NOT RDY All systems except MC1 Equipment OFF, not installed, or initializing.
OFF RDR, MPCD, UFCD, CAM, IFF,
RALT, BCN, ILS, TCN, COM1, COM2,
D/L
Equipment OFF
IN TEST All systems except MC1, MC2, RWR Initiated BIT in progress.
SF TEST FLIR, NFLR, SMS, RDR, MPCD,
UFCD, RALT, WPNS, LTDR, DFIRS,
GPS ALE-47, ALE-50, DBFS, ECS, FADEC
Self test in progress (cannot be operator
terminated).
GO All systems Initiated BIT completed without failure.
DEGD All systems except MC1, MC2 Failure detected; equipment operation
degraded.
DEGD
+
OVRHT
LDT, FLIR, NFLR, SMS, MPCD,
UFCD, CAM, CSC, FCSA, FCSB, INS,
ASPJ, RWR, LTDR, DFIRS, ALE-50,
FADEC
Detected failure and overheat.
Figure 2-51. Equipment Status Messages (Sheet 1 of 2)
A1-F18EA-NFM-000
I-2-160 ORIGINAL
STATUS
MESSAGE
APPLICABLE SYSTEM MESSAGE DEFINITION
OVRHT LDT, FLIR, NFLR, SMS, MPCD,
UFCD, CAM, CSC, FCSA, FCSB, INS,
ASPJ, RWR, LTDR, DFIRS, ALE-50,
FADEC
Overheat.
MUX FAIL CLC, FLIR, NFLR, SMS, RDR, LDDI,
RDDI, MPCD, CSC, MC2, FCSA,
FCSB, INS, COM1, COM2, D/L, ASPJ,
AISI, SDC, MU, LTDR, DMC, DFIRS,
GPS, ALE-47, ALE-50, ECS, FADEC
Equipment is not communicating on
AVMUX and on/off discrete is set to
on.
RESTRT All systems except MC1, MC2, RWR,
FADEC
Reinitiate BIT; equipment did not respond
to BIT command, remained in
BIT too long and was terminated by
MC.
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NATOPS Flight Manual 飞行手册 1(114)
