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LEFT FCC RIGHT FCC
Autopilot/Flight Director Interchannel Data Schematic
Figure 1
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747-400
MAINTENANCE MANUAL
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747-400 MAINTENANCE MANUAL
c) Two packed input discrete words. One word contains spare discretes. The second word is reserved for strapping pins.
d) Two test words are generated by each FCC. These words verify the validity of the intercommunication paths. e) Nineteen Inertial Reference Unit (IRU) signals contain vertical and lateral navigation data in BNR format.
f) Eight Air Data Computer (ADC) signals contain altitude, angle of attack, mach, airspeed, impact pressure data, and maximum operating speed in BNR format.
g) Three Instrument Landing System (ILS) signals contain selected runway heading, localizer and glideslope deviation in BNR format.
h) Three Flight Management Computer (FMC) signals contain vertical and lateral navigation data in BNR format. i) Flap position, stabilizer position, and radio height data in BNR format. j) Heading and altitude reference data in BNR format for power-up synchronization.
(c) Analog Discrete Signals 1) Servo engage discrete signals are generated by hardware from center, left, and right FCCs. The FCC's hardware logic uses this as part of the information to establish autopilot disconnect warnings, to inhibit the servo detent comparators from causing a disengagement when not multi-channel, to enable the aileron exceedance limit when single channel, and to preclude inadvertent rudder engagement due to undetected FCC malfunction.
2) Detent comparator trip discrete signals are generated by hardware from center, left, and right FCCs. The FCCs use this information to ensure a total disconnect when dual channel and only one channel trips its hardware detent comparator and to ensure that a voter-detected loss of sensor data in one channel can disengage the other channel when dual channel.
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747-400 MAINTENANCE MANUAL
YAW DAMPER SYSTEM - DESCRIPTION AND OPERATION
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1. General_______
A. An inherent characteristic of all swept back wing aircraft is a yawing motion that induces sideslip and roll. The Yaw Damper System (YDS) provides commands to the rudder that will dampen oscillations due to dutch roll and gust induced sideslip, provide turn coordination and suppress turbulence induced structural body bending modes.
B. The YDS commands drive the rudder power control modules which control the rudder mechanical linkage and rudder power control actuators. Rudder displacement commands are proportional to yaw rate. Roll attitude and true airspeed inputs are used to compute turn coordination commands.
C. Control Panel
(1) The passenger oxygen and yaw damper panel on overhead panel (P5) provides control and indication of yaw damper engagement status. The panel indicates a yaw damper ON and inoperative (INOP) state.
D. Yaw Damper Modules
(1)
The YDMs send status information to its control panel switch and all three EFIS/EICAS Interface Units, maintenance information to the Control Maintenance Computers, and electrical control commands to its associated YD actuator.
(2)
Each yaw damper module (upper or lower) receives sensor inputs from the following to compute rudder commands appropriate to flight conditions:
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