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 9.20.9
Normal Mode Pitch Control
In the normal mode, the airplane pitch control characteristics are similar to
conventional airplanes. The control column input commands the PFCs to generate
a pitch maneuver where the rate is dependent on column displacement. The PFCs
automatically position the elevator and stabilizer to generate the commanded
maneuver. The PFCs constantly monitor airplane response to pilot commands and
reposition the elevator and stabilizer accordingly. Airplane pitch responses to
thrust changes, gear configuration changes, and turbulence are 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
column back pressure.
As airspeed changes, the PFCs provide conventional pitch control characteristics
by requiring the pilot to make control column inputs or trim changes to maintain
a constant flight path.
Primary Pitch Trim Control
Primary pitch trim is controlled by the dual pitch trim switches on each control
wheel. Both switches must be moved to command trim changes. The primary
pitch trim switches are inhibited when the autopilot is engaged. Pitch trim does not
move the control column.
In the normal mode, primary pitch trim operates differently on the ground than it
does in flight. On the ground, the stabilizer is directly positioned when the pilot
uses the pitch trim switches. In flight, the pitch trim switches do not position the
stabilizer directly, but make inputs to the PFCs to change the trim reference speed.
The trim reference speed is the speed at which the airplane would eventually
stabilize if there were no control column inputs. Once the control column forces
are trimmed to zero, the airplane maintains a constant speed with no column
inputs. Thrust changes result in a relatively constant indicated airspeed climb or
descent, with no trim inputs needed unless airspeed changes.
When pilot trim inputs are made, the PFCs automatically move the elevators to
achieve the trim change, then moves the stabilizer to streamline the elevator.
Stabilizer motion may also automatically occur to streamline the stabilizer and
elevator for thrust and configuration changes.
February 15, 2010
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