D. Rudder Transfer and Solenoid Valves
(1)
The transfer and solenoid valves control hydraulic flow for yaw damper control of the rudder power control unit.
(2)
The yaw damper solenoid valve is mounted on the rudder power control unit. It is a solenoid actuated valve and is energized by the YDC when the yaw damper is engaged and B system hydraulics is pressurized. When the valve is energized, hydraulic power is supplied to the transfer valve.
(3)
The transfer valve, also mounted on the rudder power control unit, converts the yaw damper electrical signals into hydraulic flow to move the rudder. The transfer value consists of a torque motor which moves a jet pipe assembly to regulate the hydraulic flow to the control valve.
E. Autopilot Warning Light
(1) The autopilot warning light illuminates when the YDC ground maintenance mode is engaged. This annunciation provides an indication that the airplane should not be dispatched. The autopilot warning lights are illuminated by the YDC providing a ground to the autopilot accessory unit. The autopilot accessory unit provides diode isolation between the Captains and First Officers Autopilot warning lights to the YDC ground.
F. Ground Maintenance BITE (Built in Testing Equipment)
(1)
The BITE provides an integrated ground maintenance capability for the YDC. The BITE minimizes on-airplane maintenance time, reduces unconfirmed removal rates of Line Replaceable Units (LRUs), and facilitates identification of failed major components and associated interfaces.
(2)
The BITE controls are on the front panel of the yaw damper coupler (See figure 5). At the top of the panel is the output display. The output display actually consists of two individual displays, one upper and one lower. Each display contains eight 7-segment characters. The display provides menu options and test results. In the center of the panel are two rows of selector buttons. In the top row, there is the MENU, up arrow and the ON/OFF selector buttons. In the bottom row, there is the YES, down arrow and NO buttons. The up and down arrow buttons are used to scroll through menu options. The YES and NO buttons are used to respond to menu inquiries and pass test verifications. Pressing the MENU button displays the main menu. Pressing the ON/OFF button turns the BITE mode on and off.
(3)
Upon entering BITE, the autopilot warning lights illuminate to provide indication that the YDC is in ground maintenance and that the airplane should not be dispatched.
500
22-12-01 Page 6 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Sep 01/00
K06844
500 Yaw Damper Coupler BITE Control Panel
May 01/00 and Sample BITE Display Message 22-12-01
Figure 5 Page 7
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
4. Yaw Damper Operation
A. General
(1) The yaw damper augments the airplane's yaw axis stability by shaping, amplifying, and coupling quartz rate sensor and yaw damper actuator position signals to control the rudder through the hydraulic actuator.
B. Operating Modes
(1)
Initialization
(a) Prior to yaw axis engagement, the yaw damper coupler command is zero. Upon engagement, the actuator command will easy-on over a 5 second period providing a transient free transition.
(2)
Engage Interlocks and Logic
(a)
Prior to engaging the yaw damper system, the yaw damper disengage warning light is illuminated. For the yaw damper engage switch to remain engaged, the 115 volt ac and 28 volt dc must be applied to the YDC, the flight control B switch must be on, and YDC monitors must not be tripped.
(b)
The yaw damper engage switch remains in the ON position after holding the switch to ON for at least 0.1 second.
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