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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
Stabilizer Controlled Neutral Shift Functional Description
The stabilizer controlled elevator neutral shift function changes
the neutral position of the elevators during stabilizer movement.
The neutral shift function causes the elevators to move when
the stabilizer moves. The stabilizer neutral position is at 4 units
of trim. The elevator is downrigged 4 degrees when the
stabilizer is at the neutral position. When the stabilizer moves, it
moves the elevator neutral shift rods and gives a mechanical
input to the elevator PCUs. The elevator moves up as the
stabilizer moves either direction from the stabilizer neutral
position. The amount of elevator movement due to stabilizer
movement is shown by the stabilizer controlled neutral shift (not
including FCC input) line.
FCC Controlled Neutral Shift Functional Description
The primary function of the flight control computer (FCC)
controlled neutral shift is to reduce the pilot column force
necessary to trim the airplane during initial climbout after
takeoff with a forward CG and both engines operating.
The FCCs provide inputs to the mach trim actuator when these
conditions occur:
* TE flaps not up
* Either engine N1 more than 18%.
FCC controlled neutral shift changes the elevator neutral
position based on stabilizer and flap position. When active,
the FCCs command a neutral shift when any of these occurs:
* Captain or F/O stabilizer trim switches operated
* Flap setting is changed.
Manual trim wheel inputs, autopilot, and speed trim will not
command elevator movement by the FCC controlled neutral
shift function.
The incremental elevator input commanded by the FCC
controlled neutral shift varies with flap position and stabilizer
position. The amount of elevator movement due to FCC
controlled neutral shift at flap position from 1 unit to 25 units
is shown by the FCC controlled neutral shift (F1-F25) line. The
input is slightly different at flap positions of 30 units and 40 units.
The elevator input commanded by the FCC controlled neutral
shift varies in a very different manner as a function of stabilizer
setting.
FCC Controlled Neutral Shift Operation During Forward CG
Takeoffs
During forward CG takeoffs and the stabilizer at 7.0 to 10.5 units,
the FCCs input some elevator downrig. The increased airplane
nose up takeoff stabilizer settings give increased control during
takeoff.
ELEVATOR AND TAB CONTROL SYSTEM - ELEVATOR NEUTRAL SHIFT
EFFECTIVITY
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
27-31-00-016
FCC Controlled Neutral Shift Operation During Aft CG
Operations
During aft CG operations, as more airplane nose down
stabilizer trim is necessary, less elevator downrig is
commanded. This occurs as the stabilizer moves from 7 to 0
units of trim. Removal of the elevator downrig allows more nose
down control.
FCC Controlled Neutral Shift Operation During Forward CG
Landings
During forward CG landings, as the stabilizer moves from 10.5
to 17.0 units, the FCCs remove the elevator downrig and add
some uprig. By removal of the downrig and the addition of
uprig, not as much airplane nose up stabilizer is necessary to
trim. This decreases the stabilizer angle of attack and
decreases the potential for tail buffet if there is ice on the
stabilizer.
Combined Effect of Stabilizer Controlled Neutral Shift and FCC
Controlled Neutral Shift.
The elevator movement due to stabilizer position and the FCC
controlled neutral shift function add together. The total amount
of elevator movement due to stabilizer controlled neutral shift
and FCC controlled neutral shift is shown at flap positions from
1 unit to 25 units is shown by the total elevator neutral shift (F1-
F25) line.
ELEVATOR AND TAB CONTROL SYSTEM - ELEVATOR NEUTRAL SHIFT
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
27-31-00-016
ELEVATOR AND TAB CONTROL SYSTEM - ELEVATOR NEUTRAL SHIFT
ELEVATOR AND TAB CONTROL SYSTEM - ELEVATOR NEUTRAL SHIFT
EFFECTIVITY
GUN ALL 27-31-00
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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
27-31-00-016
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