(a)
Connect the electrical connector, DN120, to the pressure gage.
(b)
Put the pressure gage in its position in the panel.
(c)
Turn the panel screw in the higher left side of the pressure gage to tighten the clamp.
(d)
Remove the DO-NOT-CLOSE tag and close this circuit breaker:
1) P6 Main Power Distribution Panel a) 6D23 BRAKE PRESS IND
S 724-008
(2)
Do the steps that follow to do a test of the pressure gage:
(a)
Make sure the wheel chocks are installed.
(b)
If necessary, release the parking brake.
(c)
Supply electrical power (AMM 24-22-00/201).
WARNING: MAKE SURE THAT PERSONS AND EQUIPMENT ARE CLEAR OF ALL
_______ CONTROL SURFACES BEFORE YOU SUPPLY HYDRAULIC POWER. AILERONS, RUDDERS, ELEVATORS, FLAPS, SPOILERS, LANDING GEAR, AND THRUST REVERSERS CAN MOVE QUICKLY WHEN YOU SUPPLY HYDRAULIC POWER. THIS CAN CAUSE INJURY TO PERSONS AND DAMAGE TO EQUIPMENT.
(d)
Pressurize hydraulic system 4 (AMM 29-11-00/201).
(e)
Make sure these pressure indications are the same (+/- 100 psi): 1) The indication of the HYD BRAKE PRESS gage on the Captain's
Main Instrument Panel P1.
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747-400 MAINTENANCE MANUAL
2) The indication for hydraulic system 4 on the EICAS hydraulic synoptic display (AMM 31-61-00/001).
(f)
Remove the power from hydraulic system 4 (AMM 29-11-00/201).
(g)
Make sure hydraulic systems 1 and 2 are not pressurized (AMM 29-11-00/201).
(h)
Do this sequence of steps to do a check of the pressure gage: 1) Make sure the pressure indication of the HYD BRAKE PRESS gage, on the P1 panel, is 3000 +/- 200 psi.
2) Slowly push one set of brake pedals to the limit of travel, hold momentarily, and then release. Repeat this cycle six times.
3) Make sure the pressure indication of the HYD BRAKE PRESS gage decreases during manual brake operation.
E. Put the Airplane Back to Its Usual Condition
S 864-014
(1) Remove electrical power, if it is not necessay (AMM 24-22-00/201).
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HYDRAULIC BRAKE PRESSURE SWITCHES - REMOVAL/INSTALLATION
________________________________________________________
1. General_______
A. There are two hydraulic brake pressure switches for the brake hydraulic system:
(1)
The alternate brake hydraulic system pressure switch
(2)
The hydraulic system 4 pressure switch.
B.
This procedure contains two tasks:
(1)
The removal of these hydraulic brake pressure switches
(2)
The installation of these hydraulic brake pressure switches.
C.
These pressure switches control these indications:
(1)
The BRAKE SOURCE light in the Captain's Main Instrument Panel, P1.
(2)
The EICAS message BRAKE SOURCE (caution).
D.
The BRAKE SOURCE light and the EICAS message BRAKE SOURCE (caution) come on when there is low pressure in hydraulic systems 4, 1, and 2.
E.
The pressure switches operate independently of the hydraulic brake pressure transmitter that supplies the input to the HYD BRAKE PRESS gage. The HYD BRAKE PRESS gage is on the Captain's Main Instrument Panel, P1. The hydraulic brake pressure transmitter measures only the pressure in the hydraulic brake accumulator. Thus, the pressure in the hydraulic brake accumulator can be normal, and the pressure in hydraulic systems 4, 1, and 2 can be low. Also, the pressure indication of the HYD BRAKE PRESS gage can be normal (3000 +/- 200 psi) while the BRAKE SOURCE light is on.
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