C.
Install the Mid Spar Access Door
S 944-008
WARNING: OBEY ALL THE FUEL TANK PURGING AND ENTRY PRECAUTIONS.
_______ YOU CAN CAUSE AN INJURY TO A PERSON AND CAUSE DAMAGE TO THE AIRPLANE.
(1)
Go into the main tank (AMM 28-11-00/201).
S 424-009
(2)
To install the mid spar access door, do these steps:
(a)
Fully clean the access door opening and the access door sealing surfaces with a lint-free cloth, moist with a solvent.
(b)
Put the mid spar access door through the opening in the fuel tank and put it in its position.
(c)
Install the mounting bolts and washers.
(d)
Tighten the mounting bolts to 100-180 pound-inches.
(e)
Install the lock wire and safety seal (if necessary) between the two mounting bolts with lockwire provisions (Fig. 402).
S 944-010
(3) Make sure that the tank interior is clear of all tools, equipment, material and personnel.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 747-400 MAINTENANCE MANUAL
(4) S 414-011Go out of and close the main tank.
(5) S 414-012Install the main tank access door(s) (Fig. 401) (AMM 28-11-02/401).
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28-11-25
ALL ú ú 01 Page 407 ú Jun 10/96
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
FUEL VENT SYSTEM - DESCRIPTION AND OPERATION
____________________________________________
1. General_______
A. The fuel vent system provides positive venting of the fuel tanks to atmosphere during all attitudes of the airplane. Venting of the fuel tank is accomplished through sealed hat-shaped upper skin stringers in the wing interconnected with drain and vent tubing. The ducts in each wing are vented into a vent surge tank and overboard through a vent scoop near the wingtips.
B. The expansion space above the fuel in the tank shifts according to attitude changes of the airplane. To provide venting to atmosphere adequate under any operating condition, inboard and outboard vent ports are provided in each wing tank, and left and right vent ports are provided in the center wing tank. The ports are located so that at least one port is open to the expansion area at all times.
C. Fuel vent float valves are installed on wing vent ports at various locations to prevent fuel from entering the vent system and flowing into the wing surge tank, when the airplane is in a wing-low attitude. Float valves are located on the rear vent ports in the center wing tank to prevent fuel from entering the wing vent system when the airplane is nose-up.
D. Each vent port is connected to the hat-shaped ducts in the wing stringers by a large tube and elbow. Float-actuated drain valves are installed at low points in the tubes to allow fuel trapped in the vent lines to drain back into the tank when normal flying attitude is established.
E. Fuel surges too large to be trapped in wing vent ducts are directed to surge tanks located near the wingtips. Fuel in the surge tanks will drain back into the inboard main tanks through two drain lines and check valves located between the lower wing stringers.
F. A flame arrester in each surge tank vent outlet duct prevents flame entry into the tank from an external source at the vent outlet.
G. To protect wing structure against positive and negative overpressure, two-way pressure relief valves are installed in both wing surge tank access doors.
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