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747-400 MAINTENANCE MANUAL
(c)
If you find the leak path you can see how fuel gets from the internal leak source to the external leak point.
(d)
To understand the leak, examine the fuel tank structure and sealant.
TASK 28-11-00-206-087
4. Fuel Tank Leak Detection (Fig. 603, 604, 605, 606, 607, 608)
________________________
A. General
(1)
After you find the external fuel leak, it is necessary to find the internal leak source. Procedures to find the internal leak source include:
(a)
Air Pressure and Bubble Solution (Backblowing) Method (recommended procedure)
(b)
Air Bubble with Hollow Bolt Method
NOTE: This procedure finds leaks in areas with complex
____
structure.
(c) Dye Injection with Hollow Bolt Method
NOTE: This procedure finds leaks in areas with complex
____
structure.
(d) Dye Injection Method
NOTE: This procedure puts dye into the leak from outside
____ the fuel tank and looks for dye inside the fuel tank.
(2)
If the airplane cannot be refueled or after the other methods have been tried, these tasks can be used to find external fuel leaks:
(a)
Wing Fuel Tank - Air Pressure Leak Check
(3)
Another method to find internal and external leaks is the HeliTest Wing Kit. This method uses helium to find leaks. A leak check task is included to use the Helitest equipment.
B.
References
(1)
AMM 28-11-00/201, Fuel Tanks
(2)
AMM 28-11-00/801, Fuel Tanks
(3)
AMM 28-11-01/401, Center Wing Tank Access Door
(4)
AMM 28-11-02/401, Reserve and Main Tank Access Door
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Backblowing Procedure (Example)
Figure 606
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A77936
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MAINTENANCE MANUAL
WING STRUCTURE
LEAK TRACING DEVICE (F71329)
RUBBER SEAL
GASKETS
VEE SLOT
AIR BLEED HOSE
CLAMP
AIR OR DYE
SUPPLY HOSE
TO THE DYE PRESSURE CONNECTION OF THE SPECIAL LEAK TRACING DEVICE OR AN EQUIVALENT DEVICE
1
ADAPTER ASSEMBLY - FUEL LEAK TRACING HOLLOW BOLT (F70206-1)
1 MONITOR THE PRESSURE EQUIPMENT CONSTANTLY TO MAKE SURE THE PRESSURE IS NOT MORE THAN THE MAXIMUM SAFE PRESSURE.
Hollow Bolt for Areas With Complex Structure
Figure 607
A77939
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____DRAIN THE MANOMETER AFTER YOU
NOTE:
USE IT TO PREVENT FREEZING.
USE THE VALVE TO ADJUST THE FILL LEVEL AND TO DRAIN THE TUBING USE THE VALVE TO DRAIN THE OVERFLOW TRAP
Water Manometer Assembly
Figure 608
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