LEADING EDGE SLATS -KRUEGER FLAP MECHANISM
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777 AIRCRAFT MAINTENANCE MANUAL
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LEADING EDGE SLATS -FUNCTIONAL DESCRIPTION -PRIMARY MODE CONTROL
General
Only one FSEU commands the slats in the primary mode.
In the primary mode, the FSEU controls:
*
Slat retraction and extension
*
Flap/slat sequence
*
Cruise inhibit
*
Hydraulic isolation (CHIS)
*
Autoslat extension
*
Low-speed control
*
Shutoff control.
For redundancy, both channels in the FSEU must agree on the slat command. Each channel controls switches that are connected in series. Both channels must send the same command to the switches for the FSEU to energize the commanded solenoid.
The two coils in each solenoid of the primary control valve receive electrical power from different power sources. The FSEU controls the ground for one of the coils in each solenoid.
The FSEU also controls the solenoid in the autoslat priority valve.
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Slat Retraction and Extension
The FSEU compares the flap lever position to the slat position. The slats retract if the flap lever position is less than the slat position. The slats extend if the flap lever position is greater than the slat position.
Flap/Slat Sequence
This function controls the sequence of the retraction and extension of the flaps and slats.
See the high lift control section for more information about the primary mode flap and slat sequence (SECTION 27-03).
Cruise Inhibit
This function prevents slat extension during cruise. This happens when the airspeed is more than 250 knots or the altitude is above 20,300 feet.
Hydraulic Isolation (CHIS)
If the hydraulic quantity in the center hydraulic system reservoir is below 0.40, the FSEUs disengage the primary slat mode. The FSEUs then engage the secondary mode for the slats only. If both engines continue operating for more than 10 seconds, then the primary mode re-engages.
See the main hydraulic system section for more information about the center hydraulic isolation system (SECTION 29-10).
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LEADING EDGE SLATS -FUNCTIONAL DESCRIPTION -PRIMARY MODE CONTROL
Autoslat Extension
This function commands the slats to extend if the airplane approaches a stall condition. To make sure the slats receive enough hydraulic power, the FSEUs also command the autoslat priority valve to reduce the hydraulic flow to the main landing gear system.
Low-Speed Control
This function reduces the speed of slat movement as the slats approach the commanded position. The FSEU energizes the low-speed solenoid when the slats are less than approximately seven torque tube turns from the commanded position.
Shutoff Control
The FSEU energizes the shutoff solenoid valve to open when there is a retract or extend command.
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LEADING EDGE SLATS -FUNCTIONAL DESCRIPTION -PRIMARY MODE CONTROL
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LEADING EDGE SLATS -FUNCTIONAL DESCRIPTION -AUTOSLAT EXTENSION
General
The autoslat extension function improves the wing stall performance if the airplane approaches a stall condition. This function also makes sure the slats get enough hydraulic power when the autoslat function is active.
Autoslat
The autoslat function operates only in the primary mode and when the slats are in the sealed position. This function does not operate if the airspeed is more than 215 knots.
The warning electronics unit (WEU) sends an autoslat request to the FSEUs if the airplane approaches a stall condition. If the flap lever is in the 1, 5, 15, or 20 unit positions at this time, the FSEUs command the slats to extend to the gapped position. At this same time, the FSEUs energize the solenoid in the autoslat priority valve. This reduces the hydraulic flow to the landing gear systems. Thus, more hydraulic power can go to the slats.
The WEU also sends an autoslat request to the HYDIM cards and the air supply-cabin pressure controllers (ASCPCs). The HYDIM cards turn on both air driven pumps (ADPs). The ASCPCs operate some pneumatic valves to make sure the ADPs get enough air power.
See the main hydraulic system section for more information about the center hydraulic system (SECTION 29-10). See the pneumatic chapter for more information about the ASCPCs and the pneumatic system (CHAPTER 36).
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