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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

FUEL QUANTITY ACCESSPROCESSOR DOOR,UNIT 125B
SEE B
FWD
E6 RACK
A
SEE A
VTO
ADJUSTMENT
CARD
SEE C
HINGED DOOR
FWD
HINGED
DOOR FUEL QUANTITY PROCESSOR UNIT (HINGED DOOR CLOSED)
B
VTO OVERRIDE
FUEL QUANTITY PROCESSOR UNIT SWITCH
(HINGED DOOR OPEN)

B
SWITCH BRACKET
VTO ADJUSTMENT CARD C
VTO Override Switch
Figure 202

M26832
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 28-21-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 A. General
 (1)  
Do this task when you must refuel an airplane with an inoperative fuel quantity indicator (AMM 12-11-06/301).

 (2)  
When the fuel quantity indicator for a tank does not operate, you cannot open the applicable refuel valve using the P42 panel switch. To open the refuel valve(s) electrically, you must use the VTO override switch on the fuel quantity processor unit (FQPU). You can also manually open the refuel valve at the refuel valve control unit.

 (3)  
There is no automatic refuel valve shutoff protection when the refuel valves are opened with the VTO override switch. You must put the individual refuel valve switch to the CLOSED position before the tank overfills. If you put too much fuel into a fuel tank, fuel will overflow the tank and spill into the surge tanks.

 (4)  
The VTO override switch is found inside the Fuel Quantity Processor Unit (FQPU). The FQPU is installed on the E6 equipment rack. You can get access to the FQPU through the electronics access door, 125B.

 B.
References

 (1)  
AMM 12-11-06/301, Alternate Refueling Procedures

 (2)  
AMM 20-41-02/201, Electrostatic Discharge Sensitive Devices

 C.
Access

 (1)  
Location Zone 125 Area Below Forward Cargo Container Compartment, Left

 (2)  
Access Panel
 125B Electronics Access Panel

 D.
Put the VTO Switch to the Override Position

 S 912-022
 (1)  
Do these steps to put the VTO override switch to the ON (override) position:

 (a)  
Open the electronics access door, 125B.

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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747-400 MAINTENANCE MANUAL
 (b)  Go to the M7860 fuel quantity processor unit (View A).
 CAUTION: DO NOT TOUCH THE FUEL QUANTITY PROCESSOR UNIT BEFORE YOU
_______ DO THE PROCEDURE FOR DEVICES THAT ARE SENSITIVE TO ELECTROSTATIC DISCHARGE. ELECTROSTATIC DISCHARGE CAN CAUSE DAMAGE TO THE FUEL QUANTITY PROCESSOR UNIT.
 (c)  
Do the procedure for devices that are sensitive to electrostatic discharge (AMM 20-41-02/201).

 (d)  
Remove the screws (eight locations) from the M7860 FQPU access cover.

 (e)  
Open the FQPU hinged door (View B).

 (f)  
Remove the VTO cover plate (View C).

 (g)  
Put the VTO override switch to the ON (override) position.

 S 912-023
 (2)  
Continue with this procedure: Refuel Operation With an Inoperative Fuel Quantity Indicator (AMM 12-11-06/301).

 (a)  
Make sure the fuel quantity indicators that operate flash (1 to 2 second intervals).

 (b)  
The P42 panel refuel valve switches will control the open/close function of the refuel valves (even for the tank with a blank fuel quantity indicator).

 (c)  
With VTO override switch in the override position, there is no VTO automatic shutoff control.

 TASK 28-21-00-902-045
 5.  Put the VTO Switch to the Usual Position (Fig. 202)________________________________________
　
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