(3)
Remove dry bay access panels 7215, 7216, and 7217 (left side) or 7415, 7416, and 7417 (right side) from wing upper surface.
(4)
Install rubber stoppers in inboard and outboard dry bay drain holes.
(5)
Install test doors on dry bay access openings.
(6)
Apply and maintain 4 psi air pressure to fitting on dry bay test door.
(7)
Enter fuel tank and apply bubble solution to area suspected of containing leak source. Observe area closely for signs of bubbling solution.
(8)
If bubbles are observed, mark area inside tank and continue test until area has been completely covered.
(9)
Wipe up bubble solution using damp cloth.
(10)
If steps (6) thru (8) have not resulted in discovery of leak source, perform the following:
(a)
Remove air pressure source and allow dry bay to return to ambient pressure.
(b)
Remove dry bay test door and cover leak exit point in dry bay with spray-on fluorescent dye.
(c)
Reinstall test door and apply 4 psi air pressure to door fitting.
(d)
Enter tank with explosionproof ultraviolet light and examine dry bay area for evidence of dye.
(e)
Mark leak entry point inside fuel tank.
(11)
Remove rubber stoppers from dry bay drain holes.
(12)
Remove test doors and install dry bay access panels.
(a)
Clean the mating surfaces of the dry bay access panels and the wing skin with MEK or another approved solvent (Ref 28-11-0 AR).
(b)
Apply the parting agent to the mating surface of the dry bay access panels (Ref BAC5000).
(c)
When the parting agent is dry to the touch, apply BMS 5-26, Type II Class B sealant to the cleaned mating surface of the wing skin.
(d)
Attach the dry bay access panels to the wing skin within the sealant application time.
(13)
If internal leak point is detected, refer to 28-11-0 AR for repair procedures.
(14)
Install fuel tank access doors.
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28-11-0 Page 116 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Apr 01/97
6. Leak Path Analysis
A. After the external leak point and the internal leak source have been located, the point of seal plane penetration must be traced. The area where bubble or dye appears internally should indicate true point of seal plane penetration, except in case of a hidden seal failure. In many cases failure of an injection, prepack, or hidden type seal, will allow fuel to enter and travel within structure to appear at a point quite distant from leak source. Repairing apparent leak area, where bubbles or dye appear, and not failed hidden seal may mean a temporary fix which will have to be redone frequently until true point of penetration of seal plane is located. To prevent this situation, a fuel leak should be studied for all possible leak paths between external and internal appearance points.
NOTE: As an alternative to repairing a hidden seal, the seal plane may be raised.
B. The seal plane is the barrier that prevents escape of fuel from tank. When this seal plane is penetrated the faying surfaces of all structure on the other side of seal plane becomes wet. Wetted area extends in all directions from point of penetration until it is stopped by an injection, faying surface, or prepack type hidden seal. Fillet seals act as sides to a channel formed in the structure through which fuel will flow. Since there are no seals on other side of seal plane, any fuel that has penetrated seal plane will leak out where least resistance exists. For instance, a row of fasteners in channel may be wet, but leak will appear at only one fastener. If leaking fastener were sealed, then fastener having next least resistance will leak, and so on. Studying leak path will show how fuel got from point of seal plane penetration to outside. To get a thorough understanding of leak, study tank structure and sealant.
574
Jun 20/88 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 28-11-0 Page 117
INTEGRAL FUEL TANKS - MAINTENANCE PRACTICES
1. General
A. This procedure contains instructions for testing the fuel tanks for microbiological contamination.
2. Detection Test for Microbial Contamination
A. General
(1)
The corrosion caused by the growth of micro-organisms can be a serious problem. These micro-organisms, thriving at the interface of turbine fuel and any trapped water, are fed with the hydrocarbons of fuel and mineral salts of water. They produce deposits with corrosive action, which have the appearance of slime and vary in color from grayish-white, when dry, to muddish-brown or black, when wet with water or fuel.
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