(c)  
Rub the area with a cotton cloth to dry it.

 S 796-155
 (3)  
For running leaks, do these steps:

 (a)  
Find the origin of the leak.

 (b)  
Stop the fuel flow with mastic or tape to make sure that there are no other paths for fuel flow.

 (c)  
Mark the location of the origin of the leak.

 S 796-157
 (4)  If you find the external leak in a location that has aerodynamic smoother, remove some aerodynamic smoother around the area of the leak (AMM 51-31-01/201).
 NOTE: It is a good procedure if the hole in the smoother is
____ approximately the same as the dimensions of the nozzle that you use for the backblowing procedure.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 H. Evaluate the Fuel Leak Type
 S 796-161
 (1)  Fuel leakage is divided into four types (Fig. 601). These types are in sequence that tells you how important they are to flight safety.
 NOTE: The dimensional patterns of fuel leaks are based on an
____ examination 15 minutes after the leak area was rubbed dry (Fig. 601).
 S 796-162
 (2)  
The four fuel leak types are:

 (a)  
Stain

 (b)  
Seep

 (c)  
Heavy seep

 (d)  
Running leak

 S 796-163
 (3)  
Do these steps to evaluate the fuel leak type:

 (a)  
Rub the area with a cotton cloth to dry it.

 (b)  
Use a camel hair brush or a squeeze bottle to apply a mapping agent (talcum powder) to the area of the skin that contains the leak.

 (c)  
Monitor the talcum powder continuously to see where it changes color.

 (d)  
If the talcum powder starts to change color at the edge of the area where you applied it, apply more talcum powder at that edge.

 (e)  
Monitor the leak area with the talcum powder for fifteen minutes.

 NOTE: This will make sure you have the correct leak type and
____
 the correct leak position.

 (f)  Compare the dimensions of the leak with the dimensions shown in Fig. 601 to evaluate the type of leak.
 S 796-156
 (4)  
After you complete the analysis of the fuel leak type, do these steps:

 (a)  
Remove the talcum powder from the wing surface.

 (b)  
Make a mark at all external leak locations.

 (c)  
Make a decision to monitor or immediately repair the fuel leak(s) per the requirements of Fig. 602.

 S 866-158
 (5)
If you make a decision to monitor the fuel leak, do these steps:

 (a)  
Make a record of all leak locations (Fig. 603, 604).

 (b)  
Do this task: Put the Airplane Back to the Usual Condition.

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 S 796-159
 (6)  
If you make a decision to immediately repair the fuel leak(s), do these steps:

 (a)  
Do not defuel the fuel tanks until you know the exact location of all the external fuel leaks.

 (b)  
Review the information in this task: Analysis of Fuel Leak Cause.

 (c)  
Do this task: Fuel Tank Leak Detection.

 TASK 28-11-00-706-270
 3.  Analysis of Fuel Leak Cause (Figs. 603, 604, 605)___________________________
 A. General
 (1)  
This task lists the causes of the fuel leaks and discusses leak path analysis.

 (2)  
The cause of fuel tank leaks is usually incorrect fitting installations, damaged sealant, incorrectly installed or damaged O-rings, or loose fasteners.

 (3)  
Before you defuel a fuel tank which has a leak, try to find all of the leaks in the fuel tank.
　
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