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feet from the selected altitude.
If the airplane now climbs or descends more than 300 feet from
the selected altitude, a one-second aural warning occurs and a
flashing amber box shows around the airplane altitude display.
The visual warning stops for these conditions:
* Airplane returns to within 300 feet of the selected altitude
* You change the altitude on the MCP
* The airplanes is more than 900 feet from the selected
altitude.
Altitude Alert Conditions
One FCC supplies the warning. FCC A normally gives the
altitude alert warning. FCC B only gives the warning for these
conditions:
* FCC A baro-corrected altitude is invalid
* Only FCC B autopilot is engaged in CMD and FCC B barocorrected
altitude is valid
* Only FCC B flight director is on and FCC B baro-corrected
altitude is valid.
If the FCC captures the glideslope or the crew lowers the flaps
more than 20 degrees, the FCC does not give the altitude alert
warning.
Loss of Baro-Corrected Altitude
If the baro-corrected altitude in both FCCs is invalid and the
airplane is in the air, these events occur:
* The referenced altitude and its display on the MCP goes to
50,000 feet
* The visual warning display on the CDS flashes
* A single aural warning occurs.
The crew cannot change the selected altitude display, but if they
turn the altitude select knob, the visual warning stops.
If one of the FCC baro-corrected altitudes becomes valid, the
altitude alert warning stops and the crew can change the
selected altitude on the MCP.
DFCS - FUNCTIONAL DESCRIPTION - ALTITUDE ALERT
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-11-00-067
DFCS - FUNCTIONAL DESCRIPTION - ALTITUDE ALERT
DFCS - FUNCTIONAL DESCRIPTION - ALTITUDE ALERT
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
22-11-00-067
General
The speed trim system gives automatic stabilizer trim for
positive speed stability during low-speed high-thrust conditions.
The speed trim is only operational when the autopilot is not
engaged.
The air data inertial reference unit (ADIRU) sends these signals
to the FCC for speed trim calculations:
* Computed airspeed (CAS)
* Mach
* Inertial vertical speed
* Roll angle
* Angle of attack.
The display electronic units (DEU) send the engine N1 inputs to
the FCC. The flap position sensors send the flap position data to
the FCC. The radio altimeters send altitude data to the FCC. The
FCC calculates speed trim command signals. It sends the
signals through these switches to the stabilizer trim electric
actuator:
* Column switching module
* A/P stabilizer trim cutout switch
* Stabilizer limit switches.
Speed Trim Stability
The speed trim controls the stabilizer to oppose any change of
airspeed. An increase in CAS causes a nose up trim command
to the stabilizer. A decrease in CAS causes a nose down trim
command to the stabilizer. The signals from the stabilizer
position sensors stop the commands when the stabilizer moves
the correct amount.
The FCC trims the stabilizer nose down as speed decreases
and to allow for speed trim above the stickshaker AOA and idle
thrust. When the stabilizer position reaches its limit, the trim
stops. When the trim starts to exceed the aft column cutout
position, the trim stops. The FCC stops the speed trim function if
the roll angle is more than 40 degrees.
FCC Selection For Speed Trim
Only one FCC at a time supplies the speed trim signal to the
stabilizer trim electric actuator. When the FCCs get electrical
power, FCC A supplies the speed trim signals. If power remains
on the FCCs, the on ground signal from the proximity switch
electronics unit (PSEU) switches the FCC which supplies the
speed trim signals. If one FCC fails, the other FCC automatically
supplies the speed trim signal.
Speed Trim Failure Display
The speed trim fail annunciator on the flight control module will
show when the speed trim function in the FCC meets certain
failure conditions.
DFCS - FUNCTIONAL DESCRIPTION - SPEED/AUTOPILOT TRIM BLOCK DIAGRAM
EFFECTIVITY
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
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