(a)  
Remove the microbial growth (AMM 28-11-0/701).

(b)  
Examine the fuel tank structure for corrosion (SRM Chapter 51).

(c)  
Do a biocide treatment of the fuel tanks (AMM 28-10-0/201).

(d)  
After 10 days, get a new fuel/water sample and do the microbial detection test again.

NOTE:  This test is necessary to make sure the microbial growth removal and biocide treatment processes have reduced the level of microbial contamination to an acceptable level.
1)  Make sure the all of the biocide treated fuel has been burned through the engines (a minimum of five flights).
(e) Make a record of the maintenance completed for microbial contamination.
(3)  If the test results show moderate contamination, do a biocide treatment of the fuel tanks within 10-14 days after the test results (AMM 28-10-0/201).
(a)  After 10 days, get a new fuel/water sample and do the microbiological detection test again.
NOTE:  This test is necessary to make sure that the biocide treatment was successful in reducing the microbial contamination to an acceptable level
1)  Make sure the all of the biocide treated fuel has been burned through the engines (a minimum of five flights).
(b)  Make a record of the maintenance completed.
(4)  If the test results show negligible levels of microbial contamination, then continue normal operation.
(a)  Continue to test the aircraft at the usual intervals.
Sep 01/02 28-11-0 Page 203

FUEL SYSTEM LEAK DETECTION - INSPECTION/CHECK
1.  Fuel System Helitest Leak Detection
A.  General
(1)  
A leak detection system using helium as a tracer gas provides easier detection than more traditional methods.

(2)  
Helium is a non-toxic, inert gas which does not react chemically with any other element, making it safe. Due to its small molecular mass, helium penetrates the smallest gaps. It is readily detectable due to a low concentration in the atmosphere.

(3)  
Pressurized helium around a leak point is forced back up the leak channel precisely and quickly locating the leak source.

B.  Equipment and Materials
(1) 
 Consumables

(a)  
B01002 Solvent, General Cleaning of Solvent Resistant Organic Coatings - Series 82 (AMM 20-30-82 or SOPM 20-30-82)

(b)  
G50004 Tape, Vacuum - SMS126 or SMS127

(c)  
G00252 Material, Plastic Sheet (polyethylene) -L-P-512

(d)  
G02329 Tape, High-Speed -3M #434

(e)  
Airplane Structure Cleaning Solvents (Series 82), AMM 20-30-82/201

(f)  
Fuel Tank Maintenance, AMM 28-11-0/201

(g)  
Fuel Tank Approved Repairs, AMM 28-11-0/801

(h)  
Defueling Maintenance Practices, AMM 28-23-0/201

(2) 
 Equipment

(a)  
Helitest Wing Kit - Varian Vacuum Products, Inc., 121 Hartwell Ave., Lexington, MA 02173, Phone 1-800-882-7426 (USA only)

(b)  
Helium - Compressed, Industrial Grade, Standard Cylinder

(c)  
Regulator - Pressure and Gage for Helium Cylinder

(d)  
Ventilation Equipment - Positive and Negative (to control and evacuate helium)

(e)  
Source - Compressed Air (to blow dry areas)

C.  Procedure
(1)  Do the following steps to find external leaks and to make a map of them:
NOTE: A precise map of the leak(s) must be made for this procedure.
(a)  
Clean the external wing surface around the leak area.

(b)  
Use solvent to remove grease from the area.

(c)  
Dry the area.

(d)  
Apply a mapping agent to the area. 1) Use talcum powder or a similar powder for a mapping agent.

(e)  
For running leaks, do the following steps: 1) Find the leak origin. 2) Stop the fuel flow with mastic or tape to ensure there are no other fuel flow

paths.

(f)  
When the leak is found, remove the seat from the leak site and find the leak origin precisely within the seal.

500 
May 01/00  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  28-11-0 Page 601 

(2)  
Defuel the leaking tank. Refer to Fuel Tank Defueling and/or Tank-to-Tank Fuel Transfer (AMM 28-23-0/201).

(3)  
Prepare the leaking tank for purging and entry (AMM 28-10-0/201).

(4)  
Apply compressed air to the external leak point to force back the fuel faster and to dry the area.

(5)  
Completely clean and dry the external leak point with solvent to attain the best tape adhesion.

NOTE: This step is important for successful leak detection.
　
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