(2)  
A task to install the float switch in each fuel tank.

 B.  A float switch in each fuel tank monitors the level of the fuel during the refuel procedure. The float switch stops the refuel operation when the tank is full. The electrical wires that go to the switches are in a conduit with connections that fuel cannot go through. Some wire splices are installed adjacent to the applicable conduit bulkhead fitting at the wing front spar.
 TASK 28-21-71-004-001
 2.  Float Switch Removal____________________
 A.  References
 (1)  
AMM 27-81-00/201, Leading Edge Flaps

 (2)  
AMM 28-10-00/201, Fuel Storage

 (3)  
AMM 28-11-11/401, Wing Fuel Tank Access Panels

 (4)  
AMM 28-11-31/401, Center Tank Access Panel

 B.  Access
 (1)  
Location Zone
 305 Left Fuel Tank
 405 Right Fuel Tank
 303 Left Inboard Leading Edge
 403 Right Inboard Leading Edge
 221 Center Section Fuel Tank
 302 Left Wing Outboard Leading Edge
 402 Right Wing Outboard Leading Edge

 (2)  
Access Panels
 6540 Refueling Station Access Door
 7213 Fuel Tank Access Door
 7413 Fuel Tank Access Door
 6223 Slat Access Panel (Left)
 6523 Slat Access Panel (Right)

 C.  Procedure
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 28-21-71
 ALL  ú ú 01 Page 401 ú Mar 12/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 S 654-002
 WARNING: CAREFULLY DO ALL OF THE SAFETY PROCEDURES TO DEFUEL THE FUEL
_______ TANK AND TO PREPARE TO GO INTO IT. AN EXPLOSION, BAD INJURY TO PERSONS AND DAMAGE TO EQUIPMENT CAN OCCUR.
 (1)  Prepare to go into the applicable fuel tank (AMM 28-10-00/201).
 NOTE: If you must do maintenance on the float switch conduit
____ for the center tank, you must purge the center tank and the No. 2 tank.
 S 864-003
 WARNING: MAKE SURE THAT PERSONS AND EQUIPMENT ARE CLEAR OF THE LE
_______ AND TE FLAPS AND FLAP DRIVE MECHANISMS. THE LEADING EDGE AND THE TRAILING EDGE CONTROL SURFACES CAN EXTEND AND RETRACT QUICKLY. THIS CAN CAUSE INJURY TO PERSONS OR DAMAGE TO EQUIPMENT.
 (2)  Extend the leading edge flaps (AMM 27-81-00/201).
 S 494-004
 WARNING: YOU MUST CAREFULLY DO THE STEPS IN THE TASK BELOW TO INSTALL
_______ THE LE FLAP SAFETY LOCKS. THE LE FLAPS CAN MOVE QUICKLY IF YOU DO NOT INSTALL THE SAFETY LOCKS CORRECTLY. THIS CAN CAUSE INJURY TO PERSONS OR DAMAGE TO EQUIPMENT.
 (3)  
Install the flap locks on the leading edge flaps (AMM 27-81-00/201).

 S 864-005

 (4)  
Make sure the fueling shutoff valves at the refuel station are closed.

 (5)  
Disconnect the external electrical power, if it is connected.

 S 014-007

 (6)  
Do these steps to get access to the float switches (Fig. 401):

 (a)  
Remove the access panel, No. 11, for the No. 1 tank to get access to the float switch in the No. 1 tank.

 (b)  
Remove the access panel, No. 11, for the No. 2 tank to get access to the float switch in the No. 2 fuel tank.

 (c)  
Remove the access panel for the center tank to get access to the float switch in the center tank (AMM 28-11-31/401).

 S 864-006
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

 28-21-71
 ALL  ú ú 01 Page 402 ú Mar 12/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A

737-300/400/500
MAINTENANCE MANUAL

CENTER TANK FUELING
SEE CFLOAT SWITCH SEE B
NO. 2 TANK FUELING FLOAT SWITCH (NO. 1 TANK OPPOSITE)
SEE A
ACCESS PANEL NO. 11
479 WING RIB
FUELING
FLOAT SWITCH
SEE E

BONDING
MOUNTING JUMPER
BRACKET
CONDUIT CONDUIT NUT
　
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