3. Operation
_________
 A. Functional Description
 (1)  
Antiskid system simplified (Fig. 12)

 (a)  
Four circuit breakers (ANTISKID 1-5, 2-6, 3-7, 4-8) on P11 provide 28 v dc power to the control unit. Four main wheel cards in the unit compare IRS speed data inputs with wheel speed. This results in a control signal to the antiskid valves which limit hydraulic pressure to the brakes. Two shuttle valve modules shuttle pressure between normal and alternate systems.

 (b)  
The AUTOBK ANTISKID TEST IND 1 and AUTOBK ANTISKID TEST IND 2 circuit breakers on P11 provide 28 v dc power to the interface/display card for BITE functions. A data bus provides all the tie-ins between wheel cards, autobrake card, BITE card, and the interface/display card. The control unit provides fault signal to the EICAS computers and the ANTISKID light.

 (c)  
Inputs to control unit affecting antiskid functions include IRS speed data, and landing gear and parking brake lever position signals. The parking brake valve is checked for open to ensure antiskid function.

 (2)  
Antiskid electrical power and system inputs (Fig. 13)

 (a)  
Four individual circuit breakers (ANTISKID 1-5, 2-6, 3-7, and 4-8) on panel P11 supply 28 v dc power to four wheel cards in the control unit. The AUTOBK ANTISKID TEST IND 1 and AUTOBK ANTISKID TEST IND 2 circuit breakers on P11 provide 28 v dc power for BITE functions.

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A
757
MAINTENANCE MANUAL

R HYD SYS PWRNORMAL BRK
NORMAL BRKMTR VALVE
MTR VALVE AUTOBRAKE
IRS IRU R MODULE
SWITCHING IRU CTR AUTOBRAKE
AUTOBRAKESHUTTLE
SHUTTLE IRU L
VALVE
VALVE AUTO-BRAKE
PARK
BRAKE
VALVE
CARD
ANTISKID VALVES  ANTISKID VALVES 28V DC
AUTOBRKS/ANTISKID
L HYD SYS PWR
TEST IND 2

BRAKERELEASE
28V DC
ANTISKID 1-5

ALTN BRK
ALTN BRKMETER VALVE METER VALVE
BRAKE
28V DC

RELEASE
ANTISKID 4-8

ANTI-
GEAR DOWNSKID
28V DC AND LOCKED ALTN ALTN
CARDS ANTISKID ANTISKID
ANTISKID 2-6
ANTISKID ANTISKIDPROX SW ELEX
(4) SHUTTLE
SHUTTLE VALVE
VALVES VALVESVALVE
UNIT (PSEU)
28V DC
ANTISKID 3-7

FWD WHL SPDXDCR(8 PLACES)
1
234LOCKEDWHEELPROTECTION
5
6 7
8
L IRS SPEED REF
28V DC

INTER-FACE/ BRAKES
HYDROPLANE PROTECTON
LED
(TYP 8 PLACES)TEST IND 1AUTOBRKS/ANTISKID DISPLAYFAULT CARD R IRS SPEED REF
P11 RELAYS DISPLAY
ANTISKID
PARKING BRAKE
VALVE
ANNUNCIATOR PANEL

BITE
CARD
RIGHT &
ANTISKID
SYSTEM PRESS.

ALTERNATE
HYD SYS
METERED PRESS.L/R EICAS CMPTR

ANTISKID/AUTOBRAKE
CONTROL UNIT

RETURN
Antiskid System Simplified
Figure 12

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MAINTENANCE MANUAL

ANTISKID/AUTOBRAKE CONTROL UNIT
NOTE: ANTISKID CONTROL FOR LEFT GEAR

BRK RELEASE
WHEELS SHOWN, RIGHT SIMILAR COMMAND

Antiskid Control SchematicFigure 13 (Sheet 1)

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MAINTENANCE MANUAL

NO. 1 ANTISKID VLV
BRK BRK
ON

OFF
MODULE A
FILTERELEMENT
NO. 5 A/SNO. 6 A/S NO. 2 A/S
VLV VLVVLV

RIGHT HYDSYS PRESS
INTERNALS INTERNALS INTERNALS
SAME SAME SAME
AS ASAS
NO. 1 NO. 1 NO. 1

SHUTOFF VLV
ANTISKID ANTISKID ANTISKID
VLV VLV VLV

MTR PRESS
NORM RETURNB
NORM. ANTISKID NO. 1 & 2
VLV MDL HYD FUSE (TYP) ALTN A/S VLVBRK BRK ON
OFF
FLT DISPATCH PLUG E (4 PLS)
NO. 5 & 6ALTN A/S VLV
INTERNALS
SAME
AS
NO. 1 & 2

ANTISKID ALTN LEFT (ALTN)
SHUTTLE VLV MDL F ANTISKID
HYD SYS VLV
PRESS
MTR PRESS
ALTN RETURN
1
2
A
C
2

BRAKES  BRAKES2
NO. 1 ANTISKID NO. 2 ANTISKIDXDCR XDCR C ALTN ANTISKID VLV MDL
D 5
6
B
D
2

BRAKES  BRAKES2
FWD
NO. 5 ANTISKID NO. 6 ANTISKID
XDCR XDCR

SYSTEM PRESS.
METERED PRESS.2  TO ANTISKID/AUTOBRAKE
CONTROL UNIT (SH 1)

RETURN
Antiskid Control Schematic
Figure 13 (Sheet 2)

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