All fuel to be used by the engines and the auxiliary power unit is kept in the No. 1 and No. 2 tanks in the wing and the center tank.

A.The No. 1 and No. 2 tanks are found in the wings between the front and rear spars from the wingtip surge tank inboard to the tank end rib just inboard and forward of the main landing gear.

B.The center tank is found in the airplane fuselage, between LBBL 70.54, RBBL 70.59 and the extension of the front and rear wing spar. Two beams are along the span between the No. 1 and No. 2 tank ends and supply three cavities to keep the fuel. The three cavities are interconnected at the top and bottom of the beams along the span by fuel flow equalizing holes.

A.Integral fuel tanks, No. 1, No. 2, and center, keep fuel that is necessary to operate the engines and the auxiliary power unit. A surge tank, outboard of the No. 1 and No. 2 tank, collects fuel overflow and includes equipment to vent the fuel tanks overboard.

B.The fuel tanks hold the necessary equipment for the refuel operation (AMM 28-21-00/001), defueling (AMM 28-23-00/201), and engine fuel feed (AMM 28-22-00/001). Equipment necessary for fuel quantity indicating system is also contained in the fuel tank structure.

C.Fuel Tank Construction

(1)Primary wing structure is used for the airplane fuel tanks. The tanks are found between the front and rear wing spars and between the upper and lower wing skin. Solid "tank end" ribs close the ends of each tank, while all other wing ribs act as fuel baffles to minimize fuel slosh.

(2)The wing structure let fuel flow inboard. Fuel sump areas are found at the lowest point of each tank. Sump drain valves at these sump areas let contaminants be drained from the fuel tank. The sump drain valves also lets all fuel that remains after a tank is defueled to be removed.

(3)All fuel tanks are fluid tight. Close metal-to-metal fit of all parts forms the basic seal. Sealing compounds and sealed fasteners are used on all joints to complete the fluid tight seal.

D.No. 1 and No. 2 Tanks

(1)The No. 1 tank (left wing) and the No. 2 tank (right wing) are found in the interspar area of each wing. Two of the wing ribs contain a series of baffle check valves to prevent fuel flow away from the boost pumps.

(2)Access panels on the wing lower surface supply access to each tank. Access openings in the tank ribs are supplied for areas not accessible directly through the access panels.

(3)An overwing fill port, found on the upper wing surface, permits gravity-feed fueling if pressure fueling equipment is not available.

E.Center Tank

(1)The center tank is contained in the fuselage. It is divided into three cavities by spanwise beams. The cavities are numbered 1, 2 and 3 starting with the forward cavity. The spanwise beams contain fuel flow equalizing holes to permit flow of fuel between the beams.

(2)An access panel in the lower left surface of cavity No. 1 supplies access to the center tank. Man-size openings in the spanwise beams supply access between the cavities.

(3)The center tank has a secondary external barrier coating on the upper panel and front spar to prevent fuel vapor from entering the pressurized section of the fuselage.

F.Surge Tank

(1)A surge tank found outboard of each fuel tank in the wing contains any fuel overflow from the tanks and supplies tank venting. A surge tank drain check valve lets the fuel overflow drain back into the center tank but prevents fuel flow from the center tank to the surge tank.

2.Fuel Tank Access Panels

A.Access panels permit entry into the airplane fuel tanks for inspection or component repair. The access panels are cast aluminum or molded aluminum honeycomb and are installen in the tank. The panels are installed by inserting screws through a clamp ring on the outside, flush with wing panel and threading the screws into captive nuts in the access panel. A molded rubber seal ring, fitted into a groove in the panel seal face, supplies a static-type fluid seal between the access panel and the wing skin. Fuel tank access panels are electrically bonded to the wing structure by coating the gasket and clamp ring with anticorrosion grease.

B.The center tank has one access panel. Each surge tank has two access panels. The No. 1 and No. 2 tanks have 12 access panels each. In addition, two smaller panels in each wing supply access to the fuel boost pumps.

3.Rib and Beam Access Openings

A.Access to some equipment in the fuel tanks is not directly posssible through the access panels. For the wing tanks, rib access openings are supplied for the areas either side of access panel No. 1. For the center tank, spanwise beam access openings are supplied for access to aft cavities.

4.Overwing Fill Ports

A.An overwing fill port is supplied for No. 1 and No. 2 tanks. Each port is found on the upper wing surface. The ports permit an alternate way of fueling the wing tanks if pressure fueling equipment is not available.

B.Each overwing fill port contains an adapter, seal ring, two O-rings, a retaining nut, and a quick release filler cap. Lift and turn the handle on the filler cap in the counter-clockwise direction to unlock the filler cap. It is then lifted from the adapter. Installation reverses the procedure and the downward turn of the handle locks and seals the filler cap against the adapter.

5.Fuel Sump Drain Valves

A.Fuel sump drain valves are installed at the low points of the fuel and surge tanks to drain accumulated moisture or to drain trapped fuel remaining after defueling.

B.The sump drain valves for the No. 1 and No. 2 tank are spring-loaded closed, poppet-type valves flush-mounted in the wing lower skin. A screen over each valve inlet protects the unit from contaminants which can block the drain passages. The valve primary seal can be replaced without draining or entering the fuel tank by placing the valve in the seal service position. Removal of valve assembly requires draining and entering of tank. To drain the fuel sump, the poppet is pushed up to open the valve and let fuel drain through the drain hole in the center of the valve.

C.The sump drain valve for the center tank is a spring-loaded closed, flapper-type check valve installed in the wing lower skin in the center section. A sump drain assembly connects the valve upper housing with the lower body section of the airplane through the keel beam area. Access to the valve is through an access door stenciled SUMP DRAIN on the lower body section. The sump is drained as follows:

(1)If the sump drain valve does not have an actuating rod, insert a broad-bladed screwdriver in slot, turn clockwise and push up on the plunger. To close, release the plunger, let the slot align fore and aft, and close the access door.

(2)If the sump drain valve has an actuating rod, pull on the actuating rod. To close, release the rod and close the access door.

D.The sump drain valves for the surge tanks are spring-loaded closed, poppet-type valves flush-mounted in the wing lower skin. A screen over each valve inlet protects the unit from contaminants which can block the drain passages. The valve has a flapper valve which lets the poppet assembly be removed without draining the fuel tank. To drain a surge tank fuel sump, the poppet is pushed up to open the valve and let fuel drain through the drain hole in the center of the valve.