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and flaps 20. Asymmetry protection, uncommanded motion protection, autoslats,
and flap/slat load relief are not available in the alternate mode.
The alternate mode must be manually selected. Slat and flap operation time in the
secondary and alternate modes is greatly increased.
Flap/Slat Load Relief
In the primary mode, the flap load relief system protects the flaps from excessive
air loads. If flap airspeed placard limits are exceeded with the flaps in the 15
through 30 position, LOAD RELIEF is displayed and the flaps automatically
retract to a position appropriate to the airspeed. Load relief retraction is limited to
flaps 5.
When airspeed is reduced, the flaps automatically re–extend as airspeed allows.
Re–extension is limited to the commanded flap position.
• disables normal control
• arms the alternate mode
• engages the electric motors
• the flap lever no longer controls
flaps/slats.
787 Flight Crew Operations Manual
Flight Controls -
System Description
9.20.20 Boeing Proprietary
If a flap overspeed exists, load relief prevents flap extension beyond the 5, 15, 20,
or 25 positions until airspeed is sufficiently reduced. Flap load relief is available
only in the primary mode. The EICAS flap display indicates an in–transit flap
condition and shows actual flap position. The flap lever does not move during flap
load relief operation. Load relief for slats is not required in the primary or alternate
modes.
Slat load relief is available in the secondary mode. If airspeed exceeds 245 knots
with the slats fully extended, they retract to midrange and LOAD RELIEF is
displayed.
Autoslats
The autoslat system enhances airplane stall characteristics. Upon receiving a
signal from the stall warning system, the slats automatically extend from the
midrange position to the fully extended landing position. The slats retract a few
seconds after the signal is removed. Slats are fully extended to improve stall
handling characteristics.
Autoslat operation is armed at flaps 1, 5, 15 and 20 and is available only in the
primary slat mode.
Flap and Slat Asymmetry Detection
A detection system detects asymmetrical extension or retraction of an individual
flap. After detection, the flap drive shuts down and the EICAS message FLAPS
DRIVE is displayed.
A detection system detects slat asymmetry. Loss of all but the most outboard slats
on each wing is also detected. When slat loss or asymmetry occurs, the system
shuts down the slat drive and displays the SLATS DRIVE EICAS message.
Uncommanded Flap or Slat Motion
Uncommanded motion is detected when the slats or flaps:
• move away from the commanded position
• continue to move after reaching a commanded position
• or move in a direction opposite to that commanded.
If the flap or slat is operating in the primary mode, uncommanded motion first
causes an automatic transfer to the secondary mode. The EICAS message FLAPS
PRIMARY FAIL or SLATS PRIMARY FAIL is displayed. If motion continues,
the system shuts down. The EICAS message FLAPS DRIVE or SLATS DRIVE
is displayed.
787 Flight Crew Operations Manual
Flight Controls -
System Description
Boeing Proprietary 9.20.21
Flap Indications
Flap position indications are displayed on the primary EICAS display. A single
vertical indicator displays combined flap and slat position. The position
commanded by the flap lever is also displayed. Ten seconds after all flaps and slats
are up, the entire indication is no longer displayed. A loss of position sensing
removes the tape fill and flap lever position indications.
If flap/slat control is in the secondary or alternate mode, or if any non–normal
condition is detected, an expanded flap indication is displayed automatically. The
position of the left and right flaps and slats are separately indicated. In the
alternate mode, the position commanded by the flap lever is replaced by flap
position index marks at all flap and slat positions, and numbers at flaps 5 and flaps
20. The index marks are used as a guide to position the flaps to the desired setting.
787 Flight Crew Operations Manual
Flight Controls -
System Description
9.20.22 Boeing Proprietary
Intentionally
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787 Flight Crew Operations Manual
Flight Controls Chapter 9
EICAS Messages Section 30
Boeing Proprietary 9.30.1
9.30 Flight Controls-EICAS Messages Flight Control System EICAS Messages
The following EICAS messages can be displayed.
Note: Configuration (CONFIG) warning messages are described in Chapter 15,
Warning Systems.
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