(a)  
From the outer side of the wing tank located at the wing front spar remove these components (Fig. 601). 1) Remove the conduit nut. 2) Remove the nylon grommet. 3) Remove the rubber grommet.

(b)  
Do a check to see if the leakage is from the inner surface of the conduit or the bulkhead union seal.

(c)  
Use the flexible plastic tube and the vacuum source (a small syringe) to do the steps that follow.

(d)  
Remove the water or fuel that collected in the bottom of the conduit. 1) Put the flexible tube approximately 16 inches into the conduit. 2) Make sure the flexible tube is at the lowest point in the conduit. 3) Examine the fluid that you remove to see if the fluid contains fuel. 4) Fuel found in the conduit is an indication that there is a leak in the conduit.

(e)  
Defuel the applicable fuel tank (AMM 28-23-00/201).

(f)
Do this procedure: Fuel Tank Purging and Entry (AMM 28-10-00/201).

WARNING: OBEY ALL OF THE TANK PURGING AND ENTRY PRECAUTIONS. INJURIES TO PERSONS AND DAMAGE TO EQUIPMENT CAN OCCUR.

(g)  
Remove the access panel, No. 11, for the applicable tank (AMM 28-11-11/401).

(h)  
Remove the float switch conduit (AMM 28-21-71/401) to do an inspection.

(i)  
If the fuel leakage is from the conduit, replace the necessary parts of the conduit assembly.

(j)  
If the leakage is from the bulkhead union, do these steps: 1) Examine the bulkhead union to see if it is serviceable. 2) Install a new O-ring on the bulkhead union. 3) Clean the bulkhead surface where the O-ring is to seal.

(k)  
Install the float switch conduit (AMM 28-21-71/401).

500 
Sep 01/02  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  28-21-71 Page 601 

D.C. Fueling Float Switch Inspection Check  500 
28-21-71  Figure 601  Feb 20/92 
Page 602 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

E.  Put the Airplane Back to Its Usual Condition
(1)  
Replace the tank access panels (AMM 28-11-11/401).

(2)  
Install the slat access panel No. 6223/6523.

(3)  
Fill the tank with fuel and check the bulkhead union for signs of fuel leakage.

(4)  
With fuel in the wing tank, check the D.C. fueling float switch cutoff (AMM 28-21-0/501).

(5)  
Remove the leading edge flap locks (AMM 27-81-0/201).

WARNING:  BE CAREFUL WHEN YOU REMOVE THE LEADING EDGE FLAP LOCKS. LEADING EDGE FLAPS ARE FAST ACTING AND CAN CAUSE SERIOUS INJURY TO PERSONS.
3.  737-200 AIRPLANES WITHOUT VOLUMETRIC TOP-OFF UNITS; Cener Tank Fueling Float Switch Wiring Inspection
A.  Equipment
(1)  Megohmmeter - Quad Tech 1864 (or equivalent), must be able to read resistance at 500 VDC
B.  Consumable Materials
(1)  
Sealant - Proseal 860

(2)  
BMS13-54 (or equivalent) - string or tape, 75 feet minimum, 150 feet recommended, to pull the wires through the sleeves and conduit.

(3)  
Wire - Lockwire or stiff electrical wire, 25 feet to pull the wires through the sleeves

Sep 01/02 28-21-71 Page 603

C.  Procedure
(1)  Remove the fueling float switch from the center fuel tank (AMM 28-21-71/401).
NOTE:  If you plan to re-install the same float switch, then put a mark on the wires where they come out of the conduit (at the front spar). You must make this mark so that you know where you can tie the string to the wires when you pull the wires back in the conduit.  There must be no string or tape remaining in the conduit.
NOTE:  Cut the float switch wires at the splices shown in the maintenance manual. Keep the float switch wires as long as possible.
NOTE:  Attach a strong string to the wires, at the front spar, before you pull them out of the conduit.  If you use lacing tape, it is recommended that you use two or more strands. It is possible that one piece of lacing tape is too weak.
NOTE:  It will be necessary to go into the center fuel tank. Usually, it will not be necessary to go into the No. 2 fuel tank.
(2)  Look carefully at the area of the wire that was installed in the conduit.
(a)  If you find any sign of electrical arcing on the wires, then you must do one of these two options:
NOTE:  Arcing can show as very small blackened holes in the insulation, or as deformation or pitting of the copper wire.  Worn areas with a black material around the edge is not a sign of arcing. The black material is aluminum oxide.
1) OPTION 1; Replace the section of the electrical conduit where the arcing occurred (AIPC 28-20-00-26, AIPC 28-20-00-28).
　
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