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FSEU -flap/slat electronics unit

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HYDIM -hydraulic interface module

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HLCS -high lift control system

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LE -leading edge

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LVDT -linear variable differential transformer

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MAT -maintenance access terminal

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PDU -power drive unit

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retr -retract

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sec -secondary

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WEU -warning electronic unit

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777 AIRCRAFT MAINTENANCE MANUAL

LEADING EDGE SLATS -INTRODUCTION

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777 AIRCRAFT MAINTENANCE MANUAL

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LEADING EDGE SLATS -GENERAL DESCRIPTION

General

The LE slats and krueger flaps operate in one of these three modes:
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Primary mode

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Secondary mode

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Alternate mode.

The primary mode uses hydraulic power to operate the slats. The secondary and alternate modes use electrical power to operate the slats.
Primary Mode

The primary mode has a closed-loop control system. The pilot commands the slats with the flap lever. The flap lever position sensor sends input signals to the FSEUs. The FSEUs use the flap lever position to calculate the slat commands. The FSEUs also receive data from the systems ARINC 629 buses.
The FSEUs send the slat commands to the slat primary control valve. This valve supplies hydraulic power to the slat power drive unit (PDU). The hydraulic motor on the PDU then moves the slat mechanisms.
The flap/slat priority valve controls the amount of hydraulic flow to the slat primary control valve. The flap/slat priority valve gives priority of hydraulic power to the primary flight control system (PFCS) over the HLCS.
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As the slats move, the slat position sensors send feedback signals to the FSEUs. The FSEUs stop the slat commands when the feedback signals equal the commanded position.
The FSEUs use data from the systems ARINC 629 buses for the autoslat function. This function commands the autoslat priority valve to limit the flow of hydraulic fluid to the main landing gear system. This gives priority of the hydraulic power to the slats during autoslat operation. The autoslat priority valve also gives priority of hydraulic power to the HLCS over the main landing gear system during normal operations.
The FSEUs use the slat skew sensors to detect a slat skew and the position sensors to detect a slat asymmetry. In either condition, the FSEUs stop the slat drive.
Secondary Mode
The FSEUs use the secondary mode when the primary mode disengages. The secondary mode is only available in the air or during special maintenance functions.
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LEADING EDGE SLATS -GENERAL DESCRIPTION

The secondary mode also has a closed-loop control system. The pilot commands the slats with the flap lever. The FSEUs use the flap lever position to calculate the slat commands. The FSEUs then energize the secondary/alternate control relays. One relay energizes the bypass solenoid in the slat primary control valve and the clutch in the electric motor unit. This stops hydraulic power to the hydraulic motor and lets free flow through it. The electric motor clutch connects the motor shaft to the PDU gearbox. The other relays control electrical power to the slat electric motor on the slat PDU. The electric motor then moves the slat mechanisms.
As the slats move, the slat position sensors send feedback signals to the FSEUs. The FSEUs command the relays to stop the electric motor when the slats are at the commanded position.
The FSEUs use the slat skew sensors to detect a slat skew and the position sensors to detect an asymmetry or disagreement. In either condition, the FSEUs stop the slat drive.
Alternate Mode
The alternate mode has an open-loop control system. The pilot uses the switches on the alternate flaps panel to command the slats. An arm switch sends a discrete signal to the FSEUs to disengage the primary and secondary modes. The switch also energizes one of the secondary/alternate control relays. This relay energizes the bypass solenoid in the slat primary control valve and the clutch in the electric motor. This stops hydraulic power to the hydraulic motor and lets free flow through it. The electric motor clutch connects the motor shaft to the PDU gearbox.
The alternate flaps selector sends commands through the slat and flap limit switches to energize the other secondary/ alternate control relays. The relays control electrical power to the slat electric motor in the PDU. The electric motor then moves the slat mechanisms.
　
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