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Only SMYD 1 does primary yaw damping.
Put the switch to the OFF position to disengage the YDS. SMYD
1 removes power from the solenoid valve on the main rudder
PCU and, after a two-second delay, the yaw damper warning
light comes on. The warning light comes on any time the system
disengages.
Yaw Damper Indicator
The yaw damper indicator shows the rudder movement due to
primary yaw damper commands from SMYD 1. For primary yaw
damping, rudder movement is limited to 2 degrees with flaps up
and 3 degrees with flaps down. If you move the rudder with the
rudder pedals, the indicator does not show rudder movement.
To do a test of the indicator and the primary yaw damper
system, do the SMYD 1 servo test in the SMYD BITE - GROUND
TEST described at the end of this section.
YDS - OPERATION
EFFECTIVITY
SHZ ALL 22-23-00
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YDS - OPERATION
YDS - OPERATION
EFFECTIVITY
SHZ ALL 22-23-00
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-23-00-011
General
There are two SMYDs on the airplane.
SMYD 1 controls primary yaw damping and turn coordination
during normal operation. SMYD 2 operates WTRIS and standby
yaw damping, and is discussed in the WTRIS section.
(SECTION 27-24)
Engage Switch and Warning Light
You engage the primary yaw damper system (YDS) with the
yaw damper engage switch on the flight control panel and with
the FLT CONTROL B switch in the ON position. The SMYD does
a self check and two seconds later the yaw damper warning
light goes out to show that you have yaw damper operation. The
switch is held in the ON position electronically with power from
the SMYD.
Put the switch in the OFF position to disengage the YDS. After
you put the switch to the OFF position, the yaw damper warning
light comes on. The warning light comes on anytime the system
disengages.
Training Information Point
The electrical ground for the disengage light is connected in
series through both SMYDs. For normal operation, it is
necessary to have both SMYDs installed on the airplane.
The light test can be done with the master dim and test system.
SMYDs
The two SMYDs are the same. They both do stall management
and yaw damper functions. For stall management functions,
both SMYDs operate together. If one function fails, the other
SMYD will continue to do stall management functions.
Only one SMYD does yaw damping at a time. SMYD 1 does only
primary yaw damping during normal operations. SMYD 2 does
WTRIS and standby yaw damping during standby operations.
This is controlled by the FLT CONTROL A and B switches on the
flight control panel.
SMYD 1 uses the main rudder PCU to move the rudder for the
primary yaw damper function. For primary yaw damping, SMYD
1 compares its yaw damping calculations with SMYD 2 before it
sends a command to the main rudder PCU. If the SMYD 2
calculations disagree or if SMYD 2 fails, the yaw damper
function in SMYD 1 disengages even though SMYD 2 is not used
for primary yaw damping.
YDS - OPERATIONS - ENGAGE INTERLOCKS
EFFECTIVITY
SHZ ALL 22-23-00
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-23-00-012
YDS - OPERATIONS - ENGAGE INTERLOCKS
YDS - OPERATIONS - ENGAGE INTERLOCKS
EFFECTIVITY
SHZ ALL 22-23-00
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-23-00-012
General
The SMYD has these BITE functions:
* Continuous monitor
* BITE tests.
Continuous Monitor
The continuous monitor function of BITE monitors the SMYD
LRU for proper operation. When the SMYD has an internal
failure a fault is recorded in fault history. Some faults will cause
the SMYD to have no outputs for the stall management and yaw
damper functions.
BITE Tests
The BITE tests are used to do tests of components and sensors
that interface with the SMYD. They have these functions:
* Quick system test
* SMYD LRU self test
* Tests of sensors that interface with the SMYD
* Tests to show that functions are within specification
* Supports fault isolation.
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