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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-23-00-009
YDS - STALL MANAGEMENT YAW DAMPER
YDS - STALL MANAGEMENT YAW DAMPER
EFFECTIVITY
SHZ ALL 22-23-00
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D633A101-SHZ1 Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-23-00-009
THIS PAGE IS INTENTIONALLY LEFT BLANK
YDS - STALL MANAGEMENT YAW DAMPER
22-23-00
Page 22
D633A101-SHZ1 Oct 10/2002
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
General
The stall management yaw damper (SMYD) calculates yaw
damping commands using analog and digital inputs from
airplane sensors. SMYD 1 provides primary yaw damping
through the main rudder PCU.
Engage Interlock
The SMYD supplies 28v dc to the yaw damper solenoid valve on
the rudder PCU. When the solenoid energizes, it sends
hydraulic fluid under pressure to the EHSV which applies
hydraulic pressure to the yaw damper actuator to move the
rudder.
Yaw Damping
The SMYD CPU has the control law software for yaw damping.
These sensors send inputs to SMYD 1 for software calculations
for primary yaw damping:
* MCP
* ADIRUs (inertial and air data)
* Left AOA sensor
* FMC
* LVDT on main rudder PCU
* Trailing edge flap limit switch
* SMYD 2.
If SMYD 1 senses airplane unwanted yaw motion when the yaw
damper is engaged, it supplies a signal to the electrohydraulic
servo valve (EHSV). The EHSV applies hydraulic pressure to the
yaw damper actuator in proportion to SMYD 1 yaw damper
commands. The current and polarity determine amount and
direction the rudder moves. The yaw damper actuator makes a
mechanical input to the rudder PCU main control valve to move
the rudder. Yaw damper inputs are mechanically summed to
rudder pedal inputs. For primary yaw damping, these are the
limits for rudder travel:
* 2 degrees with flaps Up
* 3 degrees with flaps Down.
The LVDT on the main rudder PCU sends yaw damper actuator
position data to SMYD 1. The SMYD uses the data to compare
its commanded value with actual rudder movement.
The MCP sends data to the SMYD to show if either A/P is
engaged.
For primary yaw damping, SMYD 2 monitors the yaw damping
calculations of SMYD 1. These calculations must agree before
SMYD 1 commands rudder movement. If the calculations of the
two SMYDs do not agree, primary yaw damping disengages.
YDS - SMYD 1 - FUNCTIONAL DESCRIPTION
EFFECTIVITY
SHZ ALL 22-23-00
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D633A101-SHZ1 Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-23-00-010
BITE
The SMYD has BITE test and continuous BITE functions. It
stores failures in fault history for yaw damping and stall
management functions. You use the keypad to interface with the
BITE. The display shows test results and prompts you for input
YDS - SMYD 1 - FUNCTIONAL DESCRIPTION
EFFECTIVITY
SHZ ALL 22-23-00
Page 24
D633A101-SHZ1 Jun 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-23-00-010
YDS - SMYD 1 - FUNCTIONAL DESCRIPTION
YDS - SMYD 1 - FUNCTIONAL DESCRIPTION
EFFECTIVITY
SHZ ALL 22-23-00
Page 25
D633A101-SHZ1 Oct 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-23-00-010
General
You use the yaw damper ON/OFF switch on the flight control
panel to engage the yaw damper.
For the primary yaw damper system, there are these two
indicators in the flight compartment:
* Yaw damper warning light
* Yaw damper indicator.
The yaw damper warning light is on the flight control panel
above the yaw damper ON/OFF switch. The yaw damper
indicator is on the instrument panel.
Engage Switch and Warning Light
To engage the primary yaw damper system (YDS), put the yaw
damper engage switch on the flight control panel to the ON
position. These are the conditions necessary to engage the
primary yaw damper system:
* Hydraulic system B is ON
* Flight control B is ON.
If SMYD 1 does not detect any yaw damper faults, two seconds
later the yaw damper warning light will go off to show that there
is normal yaw damper operation. This switch is held in the ON
position electronically with a solenoid powered from the SMYD.
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