28-11-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL

 S 286-107
 CAUTION: HOLD THE AIR HOSE 1/2 INCH (13 MM) MINIMUM FROM THE AIRPLANE
_______ STRUCTURE. IF YOU DO NOT HOLD THE AIR HOSE 1/2 INCH (13 MM) MINIMUM FROM THE AIRPLANE STRUCTURE, DAMAGE TO THE SEALS CAN OCCUR.
 (4)  
The person out of the tank must use an air source (0-50 psi 0-345 kPa) with a nozzle to blow air through the external leak location (Fig. 606).

 (a)  
If the leak is small, it can be necessary to use the maximum pressure (100 psi or 690 kPa).

 (b)  
If the leak is larger, it is easier to find the leak with less pressure (for example, 50 psi or 345 kPa).

 S 286-108
 (5)  
Have the person in the fuel tank look for bubbles.

 (a)  
Look for bubbles that show the location of the leak.

 (b)  
It is also possible to feel for blowing air to find the leak.

 (c)  
Find all leak locations on the internal surface of the fuel tank.

 NOTE: It is possible that three or four internal leaks are
____ related to one external leak location. Make a signal to the person out of the tank to stop the backblowing procedure when you find all of the leaks.
 (d) Make a mark on these leak locations with the marking pen.
 NOTE: If you are not sure you found the correct leak path,
____ you can apply the bubble solution to the external leak location and blow air through the internal leaks. If air blows through the external leak location, you found the correct leak path.
 (e)  
If you see bubbles, make a mark in and out of the fuel tank at the area where you see bubbles.

 (f)  
After you do a check on the full area, do a check again on the areas where you saw bubbles to make sure you isolate the leaks.

 (g)  
Clean the bubble solution in the fuel tank.

 S 366-086
 (6)  
Make an analysis of the source and cause of the leak:

 (a)  
If the cause is related to structural damage, refer to the Structural Repair Manual (SRM 51-00-00) and do the structural repair before you apply the sealant.

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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747-400 MAINTENANCE MANUAL
 (b)  If you find a leak in a self-sealing rivet, refer to AMM 28-11-00/801 for procedures to do a temporary repair of self-sealing rivets with leaks.
 NOTE: Self-sealing rivets are frequently used in the fuel
____ tank. These rivets have a plastic collar that prevents fuel flow. They are not covered with sealant. Do not put sealant on these rivets unless you find one with a leak. The only permanent repair of a self-sealing rivet with a leak is to remove the used rivet and install a new one (reference the SRM).
 (c)  
If the cause is related to loose or damaged sealant then repair the sealant (AMM 28-11-00/801).

 I.
Air Bubble with Hollow Bolt Method (Figs. 607, 608)

 S 026-114
 (1)  Remove a fastener.
 NOTE: Refer to the structural repair manual for fastener removal.
____
 S 486-167
 (2)  Install the hollow bolt assembly F70206-1 (Fig. 607).
 S 866-179
 CAUTION:_______MAKE SURE THE FUEL TANK VENTS ARE OPEN AND NOT BLOCKED. IF THE FUEL TANK IS CLOSED (ACCESS DOORS INSTALLED AND VENTS BLOCKED) THE FUEL TANK PRESSURE CAN INCREASE AND CAUSE DAMAGE TO EQUIPMENT.
 (3)  Make sure the fuel tank vents are open.
 S 486-176
 WARNING: BLOW INTO THE MANOMETER AND MAKE SURE THE WATER LEVEL CHANGES
_______ TO MAKE SURE THE WATER MANOMETER OPERATES SAFELY. MAKE SURE THE OPEN END OF THE MANOMETER IS CLEAR. IF THE WATER MANOMETER DOES NOT OPERATE CORRECTLY, INJURY TO PERSONS OR DAMAGE TO EQUIPMENT COULD OCCUR.
 (4)  
Connect the water manometer, F72951-1 to the hollow bolt (Fig. 608).

 S 486-169

 (5)  
Connect the integral fuel tank leak tracer, F71329, to the hollow bolt (Fig. 607).

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