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lack of required information from other airplane systems, they automatically
revert to the secondary mode. The ACEs continue to receive pilot control inputs
and send these signals to the three PFCs. However, the PFCs use simplified
computations to generate flight control surfaces commands. These simplified
commands are sent back to the ACEs, where they are sent to the control surface
actuators the same way as in the normal mode.
The simplified PFC control laws used in the secondary mode affect airplane
handling qualities. All flight control surfaces remain operable. The elevator and
rudder are more sensitive at some airspeeds.
The following functions are not available in the secondary mode:
The EICAS caution message FLIGHT CONTROL MODE is displayed when the
primary flight control system is in the secondary mode. The secondary mode
cannot be manually selected.
Secondary Mode
• autopilot
• auto speedbrakes
• envelope protection
• gust suppression
• thrust asymmetry
compensation
STABILIZER
ELEVATORS
SPOILERS
AILERONS
FLAPERONS
RUDDER
Surfaces
Control
ACTUATOR
CONTROL
ELECTRONICS
FLIGHT
COMPUTERS
PRIMARY
PFCs
Generate all control
surface commands.
Pilot control inputs command the PFCs
to generate control surface commands.
The autopilot is not available.
Pilot Control Inputs
787 Flight Crew Operations Manual
Flight Controls -
System Description
9.20.8 Boeing Proprietary
Flight Control System Direct Mode
The ACEs automatically transition to the direct mode when they detect the failure
of all three PFCs or lose communication with the PFCs. The direct mode can also
be manually selected by moving the PRIMARY FLIGHT COMPUTERS
DISCONNECT switch to DISC.
In the direct mode, the PFCs no longer generate control surface commands. Pilot
inputs received by the ACEs are sent directly to the control surface actuators.
The direct mode provides full airplane control for continued safe flight and
landing. Airplane handling qualities are approximately the same as in the
secondary mode. The EICAS caution message PRI FLIGHT COMPUTERS is
displayed when the system is in the direct mode.
In the direct mode, the following functions are not available:
Direct Mode
Backup
In the unlikely event of the loss of all hydraulic power, the electrically actuated
spoiler pairs and pitch trim provide airplane control.
If there is a temporary loss of fly-by-wire electrical power, the right and left PFCs
and ACEs operate on 10-minute batteries. Normal pilot controls are available for
pitch, roll and yaw.
• autopilot
• auto speedbrakes
• envelope protection
• gust suppression
• manual rudder trim cancel
switch
• thrust asymmetry
compensation
STABILIZER
ELEVATORS
SPOILERS
AILERONS
FLAPERONS
RUDDER
ACTUATOR
CONTROL
ELECTRONICS
Surfaces
Control
FLIGHT
COMPUTERS
PRIMARY
Pilot Control Inputs
Pilot inputs command the ACEs to
generate control surface commands.
787 Flight Crew Operations Manual
Flight Controls -
System Description
Boeing Proprietary 9.20.9
If there is a complete loss of ACE signalling, direct wiring from the flight deck to
the stabilizer and a spoiler pair allow pilot control of pitch and roll using the
alternate pitch trim switches and the control wheel.
Normal Mode Pitch Control
In the normal mode, airplane pitch control characteristics are like conventional
airplanes, with improved handling qualities. Unlike conventional airplanes, the
control column does not directly position the elevator in flight. The control
column commands the PFCs to generate a pitch maneuver. The PFCs
automatically position the elevator and the stabilizer to generate the commanded
maneuver. The PFCs constantly monitor airplane response to pilot commands and
reposition the elevator and stabilizer to carry out these commands. Airplane pitch
responses to thrust changes, gear configuration changes, and turbulence are
automatically minimized by PFC control surface commands.
The PFCs also provide compensation for flap and speedbrake configuration
changes, and turns up to 30° of bank. The PFCs automatically control pitch to
maintain a relatively constant flight path. This eliminates the need for the pilot to
make control column inputs to compensate for these factors. For turns up to 30°
of bank, the pilot does not need to add additional column back pressure to
maintain altitude. For turns of more than 30° of bank, the pilot does need to add
　
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