787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Flight Controls -
System Description
Copyright © The Boeing Company. See title page for details.
9.20.10 D615Z003-TBC
In the secondary or direct modes, primary pitch trim operates the same on the
ground and in flight; the stabilizer is directly positioned when the pilot uses the
primary pitch trim switches.
Alternate Pitch Trim
Alternate pitch trim is controlled by the dual pitch trim switches located on the
control stand. Both switches must be moved to command trim changes. The
switches are linked electrically to the horizontal stabilizer trim actuator and then
mechanically to the stabilizer. Alternate pitch trim commands have priority over
primary pitch trim commands in all flight control modes. Alternate pitch trim
switches are inhibited when the autopilot is engaged. Pitch trim does not move the
control column.
In the normal mode, alternate 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 alternate pitch trim switches. In flight, the alternate pitch trim switches
make changes to the trim reference speed. This is the same normal operation as
the primary pitch trim switches (see the description in the previous topic, Primary
Pitch Trim Control).
In the secondary or direct modes, alternate pitch trim operates the same on the
ground and in flight; the stabilizer is directly positioned when the pilot uses the
alternate pitch trim switches.
Pitch Envelope Protection
The pitch envelope protection functions include:
• stall protection
• overspeed protection
• tail strike protection
These protection functions operate only in the Normal mode during manual
control and do not reduce pilot control authority.
Stall Protection
Stall protection reduces the likelihood of inadvertently exceeding the stall angle
of attack by providing enhanced crew awareness of the approach to a stall or to a
stalled condition.
Stall protection limits the speed to which the airplane can be trimmed. At
approximately the minimum maneuvering speed, the trim reference speed is
limited by inhibiting trim in the nose up direction. The pilot must apply continuous
aft column pressure, at twice the normal force, to maintain airspeed below the
minimum maneuvering speed.
February 15, 2010
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