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damaged or surges, TAC disengages because there is no accurate prediction of
engine thrust. TAC may still cause some rudder deflection in the appropriate
direction just before automatically disengaging.
TAC can be manually overridden by making manual rudder pedal inputs. TAC is
only available in the normal flight control mode.
Yaw Damping
In the normal mode, the yaw damping function provides Dutch roll damping and
is an inherent part of the integrated roll/yaw control laws.
Gust Suppression
A lateral gust suppression function reduces the effects of lateral gusts improves
lateral ride quality through yaw commands. This function is disabled in Secondary
and Direct modes. A vertical gust suppression function reduces the effects of
vertical accelerations through flaperon and elevator commands. This function is
active only with the autopilot engaged in Altitude Hold or VNAV level of flight
modes. This function is disabled in Secondary and Direct modes. Operation of
lateral and vertical gust suppression does not result in either rudder pedal or
control wheel movement.
787 Flight Crew Operations Manual
Flight Controls -
System Description
9.20.16 Boeing Proprietary
Rudder Trim
The rudder trim control can be used to command manual rudder trim in all three
flight control modes. Two rudder trim speeds are available. Low rate rudder trim
is commanded by rotating the control to the detent. High rate rudder trim is
commanded by rotating the control past the detent. Any manual trim inputs are
automatically zeroed when groundspeed exceeds 30 kts and additional trim inputs
are inhibited.
Rudder trim is displayed on EICAS. Rudder trim is also displayed on the flight
controls synoptic. The rudder trim 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 rudder trim indication automatically displays (pop-up) if any of the following
conditions are satisfied:
• on ground and groundspeed is less than 40 knots
• any of the following EICAS messages are active: PRI FLIGHT
COMPUTERS, FLIGHT CONTROL MODE, ENG SHUTDOWN L,
ENG SHUTDOWN R, ENG RAIL L, ENG FAIL R, ENG THRUST L,
ENG THRUST R.
Secondary and Direct Mode Yaw Control
Secondary and direct mode yaw control is similar to a conventional airplane.
Rudder surface deflections are proportional to rudder pedal movement. However,
pedal forces are unchanged from normal mode.
In secondary and direct modes, the rudder ratio changer is based on flap position.
With flaps up, the rudder response to pedal inputs is less than with the flaps down.
In the secondary mode:
• gust suppression is inoperative
• yaw damping is degraded
• thrust asymmetry compensation is inoperative.
In the direct mode the following are inoperative:
• gust suppression
• the manual rudder trim cancel switch
• thrust asymmetry compensation.
Spoilers
There are 7 sets of spoilers, 4 outboard and 3 inboard of the flaperons, on the upper
surface of each wing. The spoilers are numbered from left to right, 1 through 14.
Spoilers on opposing wings are symmetrically paired.
787 Flight Crew Operations Manual
Flight Controls -
System Description
Boeing Proprietary 9.20.17
Spoiler panels are used as speedbrakes to increase drag and reduce lift, both in
flight and on the ground. The spoilers also supplement roll control in response to
control wheel commands.
All three hydraulic systems supply the spoilers. Each hydraulic system is
dedicated to a different set of spoiler pairs to provide isolation and maintain
symmetric operation in the event of hydraulic system failure. Two electrical buses
also power two spoiler pairs. Failure of two spoiler panels in the air or failure of
one not down and locked spoiler panel on the ground causes the EICAS advisory
message SPOILERS to display. Failure of three or more spoiler panels causes the
EICAS advisory message SPOILER PAIRS to display.
Spoiler Speedbrake Operation
The 14 spoiler panels are used as speedbrakes.
The speedbrake spoilers are controlled by the speedbrake lever located on the
control stand. The speedbrake lever has three marked positions:
• DOWN
• ARMED
• UP.
The speedbrake lever can be placed in intermediate positions between ARMED
and UP.
In the ARMED position, the speedbrake lever is driven aft to the UP position
when the landing gear is fully on the ground (not tilted) and the thrust levers are
at idle.
On the ground when both reverse thrust levers are moved to the reverse idle
　
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