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Figure 2-53. BIT Control Display (Sheet 2 of 2)
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group pushbutton. One or more groups can be selected. Another way to select a group is to press the
group pushbutton (with the SELBIT option not boxed) on the BIT top level display and then ALL on
the group sublevel display. See figure 2-53.
2.21.3.3.3 Individual Units. Initiated BIT of an individual unit is performed by pressing the
equipment group pushbutton on the BIT top level display which contains the desired unit. The display
changes to a group sublevel display. Individual units from the group can then be tested by pressing the
pushbutton adjacent to the desired acronym. System status for all systems in the group is displayed on
the center of the display. Some systems require additional aircrew BIT input.
2.21.3.4 System BIT Steps. The following includes certain initiated BIT which require steps in
addition to pressing one of the buttons on the BIT display and reading the BIT status messages after
the test is complete. Figure 2-53 shows which initiated BIT are not allowed in flight.
2.21.3.4.1 FCS Initiated BIT (IBIT). For the FCS to enter IBIT the FCS BIT consent switch must be
held ON. This action prevents inadvertent IBIT initiation inflight for reasons of flight safety.
Control surfaces move during FCS IBIT with hydraulic power applied.
To prevent personnel injury or equipment damage, make sure personnel
and equipment are kept clear of control surfaces.
NOTE
· With the wings folded, both ailerons are Xd out, but no aileron BLIN
codes should be displayed. Even with wings folded, there are aileron
functions tested that may reveal FCS failures via valid BLIN codes.
· For FCS IBIT to start, the FCS BIT consent switch must be held for
at least 2 seconds. If not held for the required time, FCS A and FCS B
will indicate RESTRT on the BIT status line. If RESTRT is displayed,
select STOP on the FCS-MC sublevel display and then repeat
the initiation procedure.
· The FCS will not enter IBIT if the throttles are above 14° THA or
NWS is engaged.
· Do not operate any FCS related switches or move the stick or rudder
pedals while FCS IBIT is running, as this may produce false failure
indications.
· With the wings folded, a BIT status of GO will only be displayed for
approximately 2 seconds before reverting to a DEGD indication. BIT
status will return to GO when the wings are spread and locked.
· If the FCS IBIT fails, FCS A and FCS B will indicate DEGD on the
BIT status line. Note surface Xs and/or BLIN codes and contact
maintenance personnel for disposition.
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1. Select MENU-SUPT/BIT/FCS-MC on right DDI.
2. While simultaneously holding FCS BIT consent switch to ON, select the FCS push-button on the
FCS-MC sublevel display.
3. Release FCS button and FCS BIT consent switch when FCSA and FCSB BIT status indicates IN
TEST. FCS IBIT requires less than 1 minute.
NOTE
If IN TEST remains on the FCS BIT display longer than 2 minutes,
select STOP and actuate the paddle switch to exit FCS IBIT.
2.21.3.4.2 FCS IBIT. The fly-by-wire flight control system uses redundant hardware to provide
continued safe operation after component failures. The level of redundancy designed into the system
was set by component failure rates, failure mode effects, aircraft mission time, and survivability
considerations. The ability to provide safe operation is fundamentally based on the principle that there
are no undetected (e.g., latent) failures prior to flight which would compromise system redundancy. It
is not possible to have an in-flight periodic BIT (PBIT) which can detect all degradations in a
fly-by-wire system. Many redundant pathways can be tested only by setting system conditions that
would be unsafe to establish in flight (e.g., verification of the ability to shut off an actuator). Preflight
FCS BIT was designed to provide those tests and ensure the full redundancy of the flight control
system is available prior to flight. Without running Preflight FCS BIT and performing the necessary
maintenance, latent failures present in the system can result in unsafe conditions should additional
failures occur in flight.
2.21.3.4.3 FCS IBIT Operation. Preflight BIT consists of a series of tests which verify the integrity
of the flight control system processors, actuators, sensors, and cockpit interfaces.
Preflight FCS BIT begins by testing lower level functions. If preflight FCS BIT detects a fault at this
level which affect higher level functions, it halts and reports the fault(s). If preflight FCS BIT did not
halt at this point, false BLIN codes would be generated on higher level functions which depend upon
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NATOPS Flight Manual 飞行手册 1(116)
