LEADING EDGE SLATS -FUNCTIONAL DESCRIPTION -SECONDARY MODE LOAD RELIEF

General

The slat load relief function prevents damage to the slats and their support structures from large aerodynamic forces. Slat load relief limits the position of the slats as a function of airspeed.
Slat load relief operates in the secondary mode only.
Load Relief -Secondary Mode

In the secondary mode, load relief is active if the flap lever is not in the up position and the airspeed is more than 215 knots. If the flap lever is not in the up position, the slats retract to the sealed position.
The load relief command resets if the airspeed is less than 215 knots or the pilot moves the flap lever to up. If the flap lever is not in the up position, the slats extend to the gapped position.
Indication

When slat load relief is active, the LOAD RELIEF message shows on the EICAS display and the EICAS compacted engine display.
The flap/slat position indication shows the position of the flap lever and the actual position of the slats. During slat load relief, the command bar and detent number change from green to magenta and the tape shows the actual position of the slats.
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LEADING EDGE SLATS -FUNCTIONAL DESCRIPTION -ALTERNATE MODE CONTROL

General

The alternate mode operation of the slats is almost the same as the alternate mode operation of the flaps.
See the trailing edge flaps section for more information about the flaps alternate mode control (SECTION 27-51).
In the alternate mode, the alternate flap/slat switches energize relays. The relays control the electrical power to the electric motor, clutch, and bypass solenoid.
The alternate mode has these functions:
*
Primary and secondary mode disengage

*
Extend and retract control

*
Flap/slat sequence.

Primary and Secondary Mode Disengage

When you push the alternate flaps arm switch, the FSEUs receive an alternate arm discrete. The FSEUs use this discrete to disengage the primary and secondary modes.
The alternate flaps arm switch also supplies a ground for the bypass/clutch relay. The operation of the bypass/clutch relay in the alternate mode is the same as in the secondary mode.
Extend and Retract Control
When the alternate flaps selector is in the extend (EXT) position, it supplies a ground for the extend relay to extend the slats. When this relay energizes, it supplies 115v ac power to the electric motor. The slat limit switch de-energizes this relay when the slats move to their extend limit. In the alternate mode, this limit is at the sealed position.
When the alternate flaps selector is in the retract (RET) position, it supplies a ground for the retract relay to retract the slats. When this relay energizes, it supplies 115v ac power to the electric motor. The slat limit switch de-energizes this relay when the slats move to the up position.
When the alternate flaps selector is in the OFF position, the grounds for the extend and retract relays are removed. This de-energizes the relays and stops the slat movement.
Flap/Slat Sequence
During extension, both the flaps and slats extend at the same time.
During retraction, the slats do not retract until the flaps are fully retracted. The flap limit switch controls this sequence.
See the high lift control section for more information about the alternate mode flap and slat sequence (SECTION 27-03).

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SLAT POSITION INDICATION -GENERAL DESCRIPTION

Purpose

The slat position indication system measures the position of the slats and sends this data to the FSEUs. The FSEUs use this data for:
*
Slat control

*
Flap/slat position indication

*
Failure detection.

Slat Control

The FSEUs use the slat position data during the slat operation in the primary and secondary modes. These modes have closed loop control of the slats. Closed-loop control stops the slat command when the slat position equals the command.
　
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