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(2) Yaw Damper Operational Modes (Fig. 6)
(a)
The yaw damper modules provide self-tests, full flight regime yaw damping control, and turn coordination. To accomplish this, each module has eight operational modes described in the following paragraphs.
(b)
Power-Up
1) The power-up mode is entered when power is supplied to the yaw damper modules (power applied to bus). At least one FCE power supply module per channel must be operative and the bus circuit breakers must be closed. The mode can be entered when on the ground or in the air. If the airplane is on the ground, the system proceeds to the power-up test. If power up is entered in the air, the system proceeds to the flight mode via a 5-second easy-on function. Upon power-up, the yaw damper modules initialize all interfaces, latches, command, and state variables to a safe state. Also a record of all pre-existing faults are retained in nonvolatile random access memory and the YDS monitors are reset.
(c)
Power-Up Test
1) The power-up test is performed when the YDS is on the ground. The test lasts approximately 10 seconds during which time the yaw damper INOP amber light is turned on and an EICAS message is displayed. If a fault is detected, the INOP light remains on and the fault inop mode is entered. If the test is passed, the INOP light goes out, ground operational mode is entered, and the solenoid is engaged. During the power-up test, there should be no rudder actuator movement. The following tests are conducted during the power-up test: a) The channel fault disengagement test is performed for
each channel (control and monitor). It monitors disengage relay status and reports a fault if the relay does not disengage.
b) The hardware paths of the accelerometers is checked by causing each accelerometer to give a forced reading of 1g.
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KEY
OPERATIONAL STATUS NORMAL MODE TRANSITIONS NON-NORMAL MODE TRANSITIONS
Yaw Damper Operational Modes Figure 6
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c) The INOP amber light interface check is performed for each channel (control and monitor).
d) The hardware paths of the yaw damper command coincidence monitor is checked for both the control and monitor CPUs.
e) The test performs a Random Access Memory (RAM) read/write test.
(d) Ground Operational
1) The ground operational mode is entered when one of the following conditions is valid: a) Successful completion of power-up test or ground test
mode with airplane on ground b) Successful fault recovery on ground and subsequent
re-engagement c) Sensor loss recovery to at least one IRU d) Upon landing
2) During this mode, the yaw damper control law computes commands. However, the aircraft on ground status causes the control law output to convert commands to zero. Even though no output commands are possible, the INOP lamps do not turn on during the ground operational mode. The sensor cross-comparison monitors are also disabled during this mode. The ground operational mode is exited when the airplane becomes airborne, all IRUs are lost, or when the ground test is initiated by the CMC.
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