28-22-19
 ALL  ú ú 01 Page 405 ú Jun 15/98
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400 MAINTENANCE MANUAL
 S 654-025
 (10)
 Refuel the applicable fuel tank (AMM 12-11-01/301).

 S 024-037

 (11)
 Remove the motor/impeller unit from the main tank boost pump (AMM 28-22-03/401).

 S 794-027

 (12)
 Do a check for leaks on the main tank boost pump housing and inlet and discharge check valves.

 S 424-038

 (13)
 Install the motor/impeller unit in the boost pump (AMM 28-22-03/401).

 S 094-029

 (14)
 Remove the tail support equipment, if it is installed (AMM 07-11-08/201).

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 28-22-19
 ALL  ú ú 01 Page 406 ú Jun 15/98
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 1.

2.

3.

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747-400 MAINTENANCE MANUAL
 APU FUEL FEED SYSTEM - DESCRIPTION AND OPERATION
________________________________________________
General (Fig. 1)
_______
 A.  The APU fuel feed system supplies fuel to the auxiliary power unit in the tail cone. The system consists of a fuel supply line extending from No. 2 main fuel tank to the APU, drain lines with flame arresters connected to the supply line shroud, a dc motor-operated fuel pump, a fuel shutoff valve, and pressure switches to control and monitor system operation.
 B.  The system is connected to the No. 2 and No. 3 aft main boost pumps which automatically begin operation when ac power is available. The dc boost pump, which is used to intially supply the APU with fuel, is automatically shutoff when the boost pumps begin operation.
 C.  Control for the system is from the APU control switch on the pilots' overhead panel. For a description of the auxiliary power unit electrical system and its connection with the fuel system, refer to AMM 49-31-00/001, APU Engine Fuel System.
APU Fuel Supply Line (Fig. 1)
____________________
 A.  The APU fuel supply line supplies fuel from the APU fuel shutoff valve to the auxiliary power unit. The supply line consists of an aluminum tube from the fuel shutoff valve, through the center wing tank, to the center wing tank rear spar. From the rear spar aft to the APU firewall, the line consists of a series of flexible hoses coupled together and encased in a sealed shroud. The forward end of the line is connected to an adapter fitting at the rear spar. The aft end of the line connects to a stainless steel tube just forward of the APU firewall.
 B.  The fuel supply line shroud consists of several sections of aluminum tubing connected with sealed couplings. The shroud couples to a flexible metal bellows that is attached to the APU firewall. The line is installed on an incline so that any fuel in the shroud that might leak from the flexible hose will drain into the shroud drain lines.
APU Fuel Supply Line Shroud Drain (Fig. 1)
_________________________________
 A.  The APU fuel supply line shroud drains are connected to the APU fuel supply line shroud to drain residual fuel that could collect in the shroud from a leak in the flexible hose. One shroud drain is provided at each end of the APU fuel shroud. Fuel in the forward drain is collected by a manually-operated drain valve; fuel in the aft drain is drained overboard through a drain mast.
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 28-25-00
 ALL  ú ú 28 Page 1 ú Feb 15/98
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

APU SHROUD 
DRAIN LINE  APU FIREWALL 
VALVE  FITTING 
CENTER WING  SEE  C  SEE  E 
TANK FITTING 
SEE  B  APU FUEL 
FEED LINE 
SEE  D 

APU FUEL BOOST PUMP AND APU FUEL SHUTOFF
SEE A
APU FUEL
MANIFOLD APU BOOST PUMP INLET AND SCREEN
APU FUEL SHUTOFF VALVE
PUMP DISCHARGE
LINE CHECK VALVE CHECK VALVE
PRESSURE SWITCH
DISCHARGE LINE TO ENGINE FUEL MAIN TANKFEED MANIFOLD NO. 2 AFT
　
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