(3)  
Vertical Stabilizer

 (a)  The two yaw damper electrohydraulic servos are connected to the mechanical rudder linkage. The mechanical linkage is the interface between the yaw damper servos and the power control actuators, which move the rudders.

 (4)  
AIRPLANES WITH -122 YDM AND SUBSEQUENT YDM DASH NUMBERS; Modal Suppression Accelerometer

 (a)  The two modal suppression accelerometers are located in the aft cargo compartment ceiling and are accessed through the aft cargo compartment door (822).
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MECHANICAL  YAW DAMPER 
LINKAGE  RUDDER POWER  CONTROL PANEL  YAW DAMPER 
(REF)  (REF) CONTROL ACTUATORS  TEST SWITCH 
YAW DAMPER 
SERVOS 

RUDDER

FLIGHT COMPARTMENT

MODAL SUPPRESSION ACCELEROMETER
1
LEFT YAW DAMPER RIGHT YAW DAMPER
MODULE (E3-1) MODULE (E4-1)
1
AIRPLANES WITH -122
AND ON YAW DAMPER MODULES

ELECTRICAL/ELECTRONICS EQUIPMENT BAY
Yaw Damper - Component Location Figure 2
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 H.  Yaw Damper Block Diagram (Fig. 3)
 (1)  System Inputs
 (a)  The YDS uses the following inputs to determine existing conditions, rudder commands, and system operation. 1) The left, right, and center IRUs each provide roll
 attitude, roll rate, yaw rate, lateral acceleration, and ground speed. The left and right ADCs each provide true airspeed (TAS), impact pressure, and angle of attack (AOA).
 2)  The left and center hydraulic pressure switches sense normal hydraulic pressure to the left and right yaw damper servos, respectively. The air/ground relay provides an analog discrete signal indicating the airplane is airborne or on the ground.
 3)  Airplane type code is provided by program pins selectively grounded through airplane wiring. The yaw damper channel (left or right) code is also provided by program pins selectively grounded through airplane wiring.
 4)  AIRPLANES WITH -122 YDM AND SUBSEQUENT YDM DASH NUMBERS; the modal suppression accelerometers provide lateral acceleration data to their corresponding yaw damper modules.
 (2)  Yaw Damper Modules
 (a)  
The yaw damper modules contain ARINC 429 receivers (data bus input) plus software signal check and selection programmed routines. As multi-input parameters are received, a median value selector provides single valid input parameters for microprocessor calculations.

 (b)  
The yaw damper modules provide mode control for various operational conditions encountered over the full flight regime. Rudder commands computed by the modules assist turn coordination and damp undesirable yaw. Internal circuits in the modules conduct tests and exercise monitoring circuits. These provide failure indications and YDS disengagement if a fault is detected.

 (c)  
The yaw damper modules perform signal conditioning for analog rudder command outputs to the servos. Servo Linear Variable Differential Transducer (LVDT) feedback monitored by the modules determines rudder position. The two yaw damper modules are connected by an interlock to determine if both modules are installed. If one module is not installed, the interlock is open circuited. This causes the installed module to illuminate an INOP annunciator (for the absent module) on the yaw damper panel.

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