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EFFECTIVITY
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
27-32-00-508
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SWS - SMYD - DIGITAL INTERFACES
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D633A101-GUN Jun 10/2006
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.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
commands for stall management functions, yaw damping
functions, and for the WTRIS.
There are two SMYD computers and they are interchangeable
LRUs. Program pins and connections on the back of each LRU
determine whether the SMYD will operate as SMYD 1 or SMYD
2.
Stall Management
For stall management functions, both SMYDs calculate
commands for these functions:
* Stall warning
* Autoslat
* Performance data on CDS.
For stall management, both SMYDs calculate and send
commands to their on-side systems for stall warning, autoslat,
and for display of performance data on CDS. If one SMYD fails,
the other SMYD continues to do the stall management functions.
Yaw Damping and WTRIS
For yaw damping, the SMYDs calculate commands for these
functions:
* Primary yaw damping and turn coordination
* WTRIS and standby yaw damping/turn coordination.
SMYD 1 does primary yaw damping and turn coordination
during normal operations with hydraulic system B, and uses the
main rudder PCU to move the rudder.
SMYD 2 does WTRIS and standby yaw damping/turn
coordination during non-normal operations during flight
control manual reversion. It uses the standby hydraulic
system and the standby rudder PCU.
This section provides a functional description of each SMYD
system for stall management and yaw damping.
Stall Warning System and Elevator Feel Shift
The stall warning system is a stall management function that
activates the control column stick shakers when airspeed is
close to a stall. Each SMYD activates its on-side stick shaker
motor.
When airspeed is close to a stall, the SMYDs do the EFS
function by operating the EFSM which provides 850 psi
hydraulic system A pressure to the elevator feel computer
and the dual feel actuator. This causes the elevator feel force in
the feel and centering unit to increase and to counteract or
resist elevator up movement at the control column. Activation of
the EFSM occurs at an AOA of 8 to 11 degrees depending on
flap position. There are no other flight deck indications when
this system operates.
SWS - SMYD - FUNCTIONAL DESCRIPTION
EFFECTIVITY
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D633A101-GUN Jun 10/2006
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
27-32-00-510
Autoslat System
The autoslat system is a stall management function of the
SMYD. Both SMYDs command the leading edge slats to extend
from the sealed (mid-extend) to the gapped (full-extend)
position when airspeed is less than a safe margin more than
stall speed. This improves airplane control and handling
characteristics. Hydraulic pressure to arm the autoslat
function is available only for flaps 1, 2, or 5. The autoslat
system extends the slats at a less AOA value than where stall
warning (stick shaker) occurs. Each SMYD can operate the
autoslat system. See the leading edge autoslat system for more
information about the autoslat operation. (SECTION 27-83)
Performance Data
The SMYD calculates performance data to show on the CDS.
This is a stall management function. The SMYD calculates these
performance data:
* Pitch limit indicator (PLI) symbol
* Minimum and maximum operating airspeeds.
The SMYD calculates and sends the pitch limit indicator (PLI)
symbol to the CDS to show on the on-side ADI. The PLI symbol
provides a visual indication for safe maneuver margins for pitch
control during maximum performance climb and windshear
escape maneuvers. The PLI is an amber symbol that shows on
the ADI when the flaps are up or down.
The SMYD calculates minimum and maximum safe operating
speeds and sends this data to the airspeed indicator on the
outboard EFIS displays of the CDS and to other airplane user
systems. These are the speeds:
* Vmin/Vmax
* Vmvr
* Vf
* Veo.
Vmin is the minimum safe operating airspeed for a
configuration of flaps and gear. The SMYD calculates Vmin
with data such as flap position, Mach number and Angle of
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