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trim levers does not reduce column forces.
Elevator Variable Feel
The PFCs calculate feel commands based on airspeed. In general, control column
forces increase:
• as airspeed increases for a given column displacement, or
• as column displacement increases.
Tail Strike Protection
During takeoff or landing, the PFCs calculate if a tail strike is imminent and
decrease elevator deflection, if required, to reduce the potential for tail skid
ground contact. Activation of tail strike protection does not provide feedback to
the control column.
Secondary and Direct Mode Pitch Control
Airplane pitch control is different in the secondary and direct flight control modes.
The control columns now command a proportional elevator deflection instead of
a maneuver command. Secondary and direct modes do not provide automatic
pitch compensation for:
• thrust changes
• gear configuration changes
• turbulence
• flap and speedbrake
configuration changes
• turns to 30° bank angle.
787 Flight Crew Operations Manual
Flight Controls -
System Description
9.20.12 Boeing Proprietary
In secondary and direct modes, the elevator variable feel system provides two feel
force levels instead of a continuous variation with airspeed. The force levels
change with flap position. With the flaps up, the feel forces provide maneuver
force levels that discourage overcontrol in the pitch axis at high speeds. With flaps
extended (flaps 1 or greater), the feel forces decrease to provide force levels
appropriate for approach and landing.
In the secondary and direct modes, both the primary pitch trim switches and the
alternate pitch trim switches move the stabilizer directly. There is no trim
reference speed.
Stabilizer Electric Power and Non–Normal Operation
The stabilizer is powered through two channels by the L2 and R2 AC busses.
Stabilizer position commands from the PFCs and alternate pitch trim switches are
sent to each stabilizer channel to control the stabilizer.
Stabilizer Shutdown
If uncommanded stabilizer motion is sensed, the stabilizer channel that caused the
motion is automatically shut down. If a channel is inoperative due to an automatic
shutdown or another failure, the EICAS advisory message STABILIZER C or
STABILIZER R is displayed. The stabilizer remains operative through the
remaining stabilizer channel.
If both stabilizer channels automatically shut down or fail, the EICAS warning
message STABILIZER is displayed. The STABILIZER warning is also displayed
if automatic shutdown fails to stop uncommanded motion.
The L2 and R2 stabilizer cutout switches, located on the aisle stand, control
electric power to the respective stabilizer channel. Placing both switches in the
CUTOUT position removes all power from the stabilizer channels. The EICAS
advisory message STABILIZER CUTOUT is displayed when both stabilizer
cutout switches are in the CUTOUT position. The STABILIZER warning message
is no longer displayed.
In the normal flight control mode, when the stabilizer is manually shut down or
failed, pitch trim is still available. Pilot pitch trim inputs change the PFC trim
reference speed. The PFCs then reposition the elevators to trim the airplane.
The control column can be used to interrupt pitch trim commands from the wheel
pitch trim switches. This feature allows the pilot to quickly stop uncommanded
trim changes due to stuck pitch trim switches. The pitch trim commands are
interrupted if the control column is displaced in the opposing direction.
787 Flight Crew Operations Manual
Flight Controls -
System Description
Boeing Proprietary 9.20.13
Stabilizer Position Indication and Greenband
Stabilizer position is displayed on EICAS. Stabilizer position is also displayed on
the flight controls synoptic.The stabilizer position indication normally blanks
when either of the following conditions are satisfied:
• gear up for 10 seconds (corresponds to normal gear indication blanking)
• 60 seconds after liftoff.
The stabilizer position indication automatically displays (pop-up) if any of the
following conditions are satisfied:
• on ground and groundspeed is less than 40 knots
• on ground and any pair of pitch trim switches are used
• any of the following EICAS messages are active:
• PRI FLIGHT COMPUTERS
• FLIGHT CONTROL MODE
• STABILIZER
• STABILIZER CUTOUT
• PITCH UP AUTHORITY.
• PITCH DOWN AUTHORITY.
The stabilizer position indicators also display the takeoff green band indication.
The green band automatically displays the acceptable range for takeoff stabilizer
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787机组操作手册Flight Crew Operations Manual 2(72)
