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LEADING EDGE SLATS -FUNCTIONAL DESCRIPTION -SECONDARY MODE CONTROL
General
The operation of the slats in the secondary mode is the same as for the flaps.
See the trailing edge flaps section for more information about the flaps secondary mode control (SECTION 27-51).
Only one FSEU commands the slats in the secondary mode. The FSEU controls:
*
Secondary mode engage
*
Retraction and extension
*
Flap/slat sequence
*
Cruise inhibit
*
Slat Load relief
*
Secondary mode auto test.
For redundancy, both channels in the FSEU must agree on the slat command.
In the secondary mode, the FSEUs energize relays. The relays control the electrical power to the electric motor, clutch, and bypass solenoid. The alternate mode also uses these relays.
Secondary Mode Engage
When the FSEU engages the secondary mode, it energizes the bypass/clutch relay.
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See the high lift control section for more information about the mode selection (SECTION 27-03).
This relay has three functions.
First, the bypass/clutch relay supplies power to the bypass solenoid in the primary control valve. This stops hydraulic operation in the primary mode.
Second, this relay supplies power to the clutch in the electric motor. This permits the electric motor to move the slat drive system.
Third, the bypass/clutch relay supplies power to the extend and retract relays. These relays do not energize until the FSEUs supply the grounds for them.
Retraction and Extension Control
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.
Either FSEU can energize the extend and retract relays to move the slats. These relays supply 115v ac power to the electric motor.
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LEADING EDGE SLATS -FUNCTIONAL DESCRIPTION -SECONDARY MODE CONTROL
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 secondary 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.
Slat Load Relief
This function commands the slats to retract if the airspeed increases above the slat load relief limit.
Secondary Mode Auto Test
The secondary mode auto test does a test of the operation of the secondary mode. After 100 flight cycles, the FSEUs begin the test when the slats are commanded to extend. The test does these things:
*
Disengages the primary mode
*
Engages the electric motor clutch
*
Extends the slats for two seconds using the electric motor.
One flight cycle is when all of these conditions occur for two seconds:
*
Airplane not on the ground
*
Airspeed is greater than 70 knots
*
Flap lever is at up
*
Slats are at up.
When the slats extend for two seconds in the secondary mode, the test stops and the primary mode engages again. The slats then move to the commanded position in the primary mode.
If the slats fail to extend within four seconds during the secondary mode auto test, the SLATS SECONDARY FAIL status message shows.
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