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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
2) The Yaw Damper Actuator ground test mode is initiated by the CMC and is menu driven. In order to enter the Yaw Damper Actuator ground test mode, the left, center and right IRUs must be aligned and in NAV mode. In addition, the yaw damper (lower or upper) which is to be tested must be engaged via the P5 panel engage switch which will annunciate ON and the INOP annunciator will extinguish. Hydraulic systems No. 2 and No. 3 must be pressurized and FLT CONTROL POWER TAIL 2 and 3 switches located on the P461 Pilot's Overhead Maintenance Panel must be in the NORM position. Finally, the ground test enable switches have to be placed in the NORM position, one switch is located on the P461 Pilot's Overhead Maintenance Panel, the other is located in the E-E bay STA 400. Once initiated, the INOP annunciator will illuminate during the test and commands are sent to the yaw damper actuator at the rudder being tested (upper or lower). The rudder (upper or lower) will move |4 degrees during this test. If the test is passed, the ground operationalmode is entered. The fault inop mode is entered if the test fails.
(f)
Fade-In
1) The fade-in mode is entered from the power-up mode, successful fault recovery in air, or ground operational mode. The mode is entered when power is first applied or after the airplane becomes airborne. The mode prevents sudden rudder transient response. The easy-on control law provides a linear rise in gain from zero to one in 5 seconds. When a gain of one is reached, the full flight mode is engaged.
(g)
Flight Mode
1) The full flight mode is entered when the airplane is airborne and the fade-in function is completed. The flight mode performs turn coordination and yaw damping. Yaw correction and turn coordination are computed from yaw rate, lateral acceleration, indicated angle of attack, roll angle, roll rate, and true airspeed (or ground speed when true airspeed is not available). The flight mode also provides fault monitoring, self-checks, command limiting, degraded operation as required, auto-disengage, and fault indications.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
2) When IRU data is invalid, the associated yaw channel automatically disengages. Each channel is also engaged and disengaged by the YDS manual controls. The flight mode automatically exits to the ground operational mode upon landing via the fade-out function.
(h)
Fade-Out
1) The fade-out mode is entered directly upon airplane landing. The mode prevents a sudden stop of rudder control. The easy-off control law provides a linear decrease in gain from one to zero in 5-seconds time period. The transition begins as soon as a ground state is established.
(i)
Fault Mode
1) The fault mode is entered as a result of the following: a) Failure of the power-up test b) Failure of the ground test mode c) Fault monitors trip
2) The INOP light will turn on when the associated channel is disengaged or when either yaw damper switch is pushed off.
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