787 Flight Crew Operations Manual
DO NOT USE FOR FLIGHT
Flight Controls -
System Description
Copyright © The Boeing Company. See title page for details.
9.20.20 D615Z003-TBC
Selection of flaps 30 commands the flaps to extend to the primary landing
position.
During retraction, flap and slat sequencing is reversed.
The mechanical gate at the flaps 20 detent prevents inadvertent retraction of the
flaps past the go–around flap setting. The mechanical gate at flaps 1 prevents
inadvertent retraction of the slats past the middle position.
Flap and Slat Modes
There are three modes of flap and slat operation:
• primary
• secondary
• alternate
In the primary mode, the flaps and slats are controlled together and positioned
using center hydraulic system motors. Autogap and flap load relief operate in the
primary mode.
The secondary mode is automatically engaged when any of the following
conditions occur:
• center hydraulic system failed, or
• flap or slat primary control failure, or
• primary mode fails to move the flaps or slats to the selected position, or
• control surfaces travel at less than 50% of the normal hydraulic rate, or
• uncommanded flap or slat motion is detected, or
• flap or slat disagree is detected
In the secondary mode the slats and flaps are controlled separately and can be
positioned by hydraulic or electric motors. For example, if the slats hydraulic
control fails, the flaps are still driven hydraulically but the slats are now powered
electrically. Pilot control is through the flap lever but operation in secondary mode
is limited to flaps 20 by non-normal procedures.
The three–position alternate flaps selector extends and retracts the flaps and slats.
The flaps and slats extend simultaneously, but slat retraction is inhibited until the
flaps are up. Alternate mode flap and slat extension is limited to the slats middle
position and flaps 20. Asymmetry and uncommanded motion protection, slat
autogap and pregap, and flap and slat load relief are not available in alternate
mode.
The alternate mode must be manually selected. Slat and flap operation time in the
secondary and alternate modes is greatly increased.
February 13, 2009
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