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Solenoid coil failure on the primary control valve for the flaps or the slats
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Flap or slat position sensor failure
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FSEU failure.
During normal conditions, the flaps and slats operate in the primary mode. If a component fails in lane 1 and lane 1 is in control, lane 2 becomes the control lane. In this condition, the flaps and slats stay in the primary mode. This failure condition causes the FLAP/SLAT CONTROL 1 status message to show.
If lane 2 is in control when a component fails in lane 2, lane 1 becomes the control lane and the FLAP/SLAT CONTROL 2 status message shows.
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HIGH LIFT CONTROL -MODE SELECTION
If there is a detected component failure in the standby lane while the control lane operates properly, the applicable status message, FLAP/SLAT CONTROL 1 or 2, shows. The control lane remains in control.
Secondary Mode Selection
After a lane change, if the original failure or an additional one prevents the flaps or slats to operate in primary mode, the FSEU in control changes to the secondary mode operation for the flaps or the slats.
If the failures are with flap components only, only the primary flap mode disengages and the flaps operate in secondary mode. The slats operation continues in the primary mode. This condition causes the FLAPS PRIMARY FAIL caution message to show. The same is true for the slats. But in this case, the SLATS PRIMARY FAIL caution messge shows.
If the failures affected both the flaps and slats, such as both FSEUs, both the primary flap mode and the primary slat mode disengage. This condition causes both the FLAPS PRIMARY FAIL and SLATS PRIMARY FAIL caution messages to show.
After the flaps and slats fully retract, the secondary mode disengages and the primary mode engages. Then the FLAPS PRIMARY FAIL and/or the SLATS PRIMARY FAIL message erases.
EFFECTIVITY
BEJ ALL
The FSEU in control engages the secondary mode for the flaps or slats if there is a flap or slat disagree in primary mode. There is a disagree when the flaps or slats do not move when commanded or move too slowly. The FSEU in control disengages the primary mode for the flaps or the slats and engage the secondary mode. This condition causes the FLAPS PRIMARY FAIL or the SLATS PRIMARY FAIL caution message to show.
When the center hydraulic system pressure is low, it does not permit the hydraulic motors to operate the flaps and slats. The FSEU in control engages the secondary mode for the flaps and slats. The operation stays in the secondary mode until the flaps and slats are in the retracted position or until the center hydraulic system pressure is more than 2000 psi after it was less than 1000 psi.
Flaps and Slats Drive Shutdown
If there are component failures that affect the operation of both flaps and slats, the flaps and slats can no longer operate in primary and secondary mode. The FLAP/SLAT CONTROL caution message shows. In addition, the FLAP/SLAT CONTROL 1 and the FLAP/SLAT CONTROL 2 status messages also show.
The FSEUs declare and latch a flaps or slats drive shut down for any one of these position failures:
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Disagreement in secondary mode (the flaps or slats do not move with a secondary mode command or move too slowly)
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Asymmetry (the flaps or slats on one wing do not align with the flaps or slats on the other wing)
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Skew (a flap or slat on one wing is out of alignment).
If there is a secondary mode disagree, an asymmetry or a skew, the FSEUs disengage both the primary and secondary modes and shut down the drive system for the flaps or the slats.
A shut down of the slats drive with the slats at the UP position, at the sealed position, or between, causes the flaps operation to be limited to the 20-unit position. If the slats are at the gapped position when the slats drive shuts down, the flaps can operate to the full extend. A shut down of the flaps drive will not let the slats extend to the gapped position.
The shut down of the flaps or the slats drive causes the FLAPS DRIVE or the SLATS DRIVE caution message to show.
Alternate Mode Selection
The only way to engage and disengage the alternate mode is to use the alternate flaps arm switch. When the pilot pushes on the alternate flaps arm switch, the primary and secondary modes disengage in both FSEUs and the alternate mode engages. This causes the FLAP/SLAT CONTROL caution message to show.
When the pilot releases the alternate flaps arm switch, the alternate mode disengages and the FSEUs try to engage the primary mode. If the primary mode is disabled, the FSEUs try to engage the secondary mode. If the secondary mode is also disabled, you must use the alternate mode to move the flaps and slats.
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