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A
747-400
MAINTENANCE MANUAL

STRINGER RIB STRINGER
SEAL ATTACHMENT
SEAL  PLANE SEALANGLE FILLETPLANE PLANESEAL
RIVET REAR SEALS RIVET SPAR HERE
REAR
WING SKIN SEALS WEB  SELF-SEALING
SPAR
HERE B  RIVETS
A
WEB
C
PREPACK WING
SEAL SKIN

SEAL
PLANE

NON-SELF-VENT DUCT SEALING RIVET SFLF-SEALING SEAL PLANE
STRINGER RIVET
D
VENT DUCT
WING SKIN FILLET SEAL
FUEL TANK SEAL PLANE E
FUEL DAM (TYPICAL)
TANK END
SEAL CAP STRINGER
F  LOWER WING SKIN
Fuel Tank Seal Plane Details
Figure 7

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747-400 MAINTENANCE MANUAL
 (d)  
An absolute seal is required to isolate spanwise vent ducts from all surrounding areas. The ducts must be sealed against external leakage and also against leakage between the vent system and the fuel tanks. Detail E shows a typical vent duct seal plane application with both interior and exterior seal planes noted. The enlarged view shows that the seal plane is maintained by self-sealing rivets. The upset head of the rivets prevent fuel in the vent duct from seeping out.

 (e)  
At the tank end ribs between the main tanks, the seal is maintained by fuel dams installed between the skin panel and the tank end rib chord and between the panel stringers and the rib shear tie on both the upper and lower surface (detail F). Each dam is shaped so that it can be installed by a faying surface and fillet seals to the interfacing structure. All fasteners that penetrate the dams are sealed with a seal cap.

 D.
Types of Seals (Fig. 8)

 (1)  
Fillet Seal (Fig. 9)

 (a)  
The basic sealant application to fuel tank structure is the fillet seal. Fillet seals are used to cover structural joints along stiffeners, stringers, tank walls, and spars, and to seal around fittings on tank walls and in corners. The dimensions shown in Fig. 9 represent typical finished fillet shapes for various gages. Fillets conform to dimensions as nearly as possible since the shape of a fillet determines how long it will last in service. A typical application of fillet seals in a tank corner is also shown in Fig. 9.

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747-400
MAINTENANCE MANUAL

UPPER WING PANEL
INJECTION SEAL
FILLET SEAL
ISOLATION SEAL
INSIDE SURFACE VENT STIFFENER
VENT PLUG
UPPER SPAR CHORD
FRONT SPAR WEB
SEAL MANUFACTURED HEAD OF RIVETS INSIDE TANK WHICH
FORWARD
PASS THROUGH JOGGLE STIFFENER
ON FORWARD STIFFENER
ISOLATION FAYING LOWER SPAR CHORD SURFACE SEAL
INJECTION SEAL
SEAL CAP
FILLET SEAL
FAYING SURFACE SEAL FOR CORROSION
STRINGER
PREVENTION
PRIMARY FAYING SURFACE SEAL
Fuel Tank Seals
Figure 8

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747-400 MAINTENANCE MANUAL
CORNER FITTINGFILLET SEAL AROUND

(a) (b) (c) (d)
dw
d
a+b = w, EXCEPT a = ZERO WHEN b = 0.25 OR MORE
0.20 MIN

0.20 MIN

................ .....
.. ............
.
GAP MUST BE FILLED, NOT BRIDGED
NOTE:ALL DIMENSIONS ARE IN INCHES.
Fuel Tank Fillet Seals
Figure 9

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