787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Flight Controls -
System Description
Copyright © The Boeing Company. See title page for details.
D615Z003-TBC 9.20.5
Primary Flight Control System Modes
There are three primary flight control system modes (flap and slat system modes
are described later in this section):
• normal
• secondary
• direct
All the modes use the same pilot controls and flight control surfaces.
Flight Control System Normal Mode
In the normal mode during manual flight the ACEs receive pilot control inputs and
send these signals to the three PFCs. The PFCs verify these signals and
information from other airplane systems to compute enhanced control surface
commands. These commands are sent back to the four ACEs, then to the flight
control surface actuators. (Refer to Flight Controls
in Chapter L, Section 10, for
additional information.)
When the autopilot is engaged, the autopilot system sends control surface
commands to the PFCs. The PFCs generate control surface commands which are
sent to the ACEs and then to the control surface actuators. The autopilot
backdrives the pilot controls to provide awareness of what the autopilot is doing.
If the pilot overrides the autopilot with control inputs, the autopilot disconnects
and the flight control system uses the pilot control inputs. The autopilot is only
available during normal mode operation. (Refer to Autopilot Flight Director
System in Chapter 4, Section 20, for additional information.)
After landing, when the hydraulic systems are shut down as part of the normal
shutdown procedure, the PFCs initiates a self-test. During the test, various EICAS
alert and status messages display, the trim indication blinks, and various failures
display on the flight controls synoptic. When the self-test is complete, the EICAS
messages are removed, and the trim indicator and synoptic display return to
normal. The test is complete about two minutes after the EICAS caution message
HYD PRESS SYS L+C+R is displayed.
Flight Envelope Protection
The flight envelope protection system reduces the possibility of inadvertently
exceeding the airplane's flight envelope. The flight envelope protection system
provides crew awareness of envelope margins through tactile, aural, and visual
cues. The protection functions operate only in the Normal mode during manual
control and do not reduce pilot control authority. The protection functions are
described later in this section and include:
• stall protection
• overspeed protection
February 13, 2009
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