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9.20.12 D6-30151-425
Flight Controls -
System Description
Spoiler Control Diagram
N_O__T_E: Numbers in boxes refer
to hydraulic systems.
UP
DN
ARM
DETENT
FLIGHT
LEFT
SPOILER
MIXER
RIGHT
SPOILER
MIXER
April 1, 2000
747 Operations Manual
Flight Controls -
System Description
Copyright © The Boeing Company. See title page for details.
D6-30151-425 9.20.13
Flaps
Increased lift and decreased stall speed for takeoff and landing are provided by
leading and trailing edge flaps. There are three groups of leading edge flaps on
each wing: outboard flap section, midspan section, and inboard section. The
leading edge flaps are normally pneumatically powered from the bleed air duct.
The trailing edge flaps consist of an inboard group normally powered by hydraulic
system 1 and an outboard group normally powered by hydraulic system 4.
Opposite trailing edge flaps are mechanically connected to maintain symmetry.
Flap Control
Flap lever position is transmitted to three identical flap control units (FCUs) which
sequence and monitor flap operation. Each FCU is capable of performing any or
all of the three basic functions: primary control, secondary control, and indication
and annunciation. They also provide trailing edge flap asymmetry protection in
the primary and secondary modes, control the flap load relief function in primary
mode only, and provide flap position information to EICAS and other systems.
The FCUs operate in two control modes, primary and secondary. In primary mode,
the FCUs drive the leading edge flaps pneumatically and the trailing edge flaps
hydraulically to the selected position. If any flap group fails to move to the
commanded position, the FCUs switch to secondary mode for the related group
driving the flap group through electric motors. The change from primary to
secondary mode for both leading and trailing edge flaps is by symmetrical flap
groups on both wings. If a primary control failure occurs in either the inboard or
midspan leading edge flap group, both groups switch to secondary mode. For all
other flap groups, only the failed group operates in secondary mode. Secondary
mode flap operation is much slower than primary mode operation. If a failure
occurs in a leading edge flap group on one wing, the flap groups on both wings
change to secondary mode. However, due to the rapid rate of primary mode flap
movement, the non-affected side completes movement before changing to
secondary mode.
If a trailing edge flap group is driven in secondary mode due to a lack of hydraulic
system pressure, the FCUs switch back to primary mode operation once hydraulic
pressure is restored. However, if a trailing edge flap group is driven in secondary
mode with hydraulic pressure available, the group remains in secondary mode
until fully retracted. For leading edge flaps, if any groups are driven in secondary
mode, the groups remain in secondary mode until they reach the commanded
position.
If a trailing edge asymmetry is detected, primary mode operation is immediately
shut down for the asymmetric group and the FCUs do not use secondary mode.
The EICAS caution message FLAPS CONTROL displays if all three FCUs fail in
their control function. EICAS flap indications from the FCUs may still be valid.
October 1, 2000
747 Operations Manual
Copyright © The Boeing Company. See title page for details.
9.20.14 D6-30151-425
Flight Controls -
System Description
An alternate control mode which bypasses the FCUs can be manually selected. All
flaps are extended or retracted by a simplified control system and electric motors.
There is no asymmetry protection in alternate mode. When the Alternate Flaps
Arm switch is pushed to ALTN, the Flap lever is inoperative. Flaps are extended
and retracted using the Alternate Flaps selector.
Flap Sequencing
When the Flap lever is moved from UP detent to flaps 1 detent, the trailing edge
flaps remain retracted and the inboard and midspan leading edge flap groups
extend. When the Flap lever is moved from flaps 1 detent to flaps 5 detent, the
trailing edge flaps move to flaps 5 position and the outboard leading edge flap
groups extend. When the Flap lever is moved to the flaps 10, 20, 25, or 30 detents,
the trailing edge flaps move to the selected position. The reverse sequence occurs
during flap retraction. Secondary mode sequencing is the same as primary mode.
During alternate control mode extension, all leading and trailing edge flap groups
begin extending immediately. Trailing edge flaps extend to a maximum position
of flaps 25. During retraction, all leading edge flap groups retract after the inboard
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