R  **ON A/C 151-199, 401-499,
 (1) Frames (Ref. Fig. 002A) Frames are the circular stiffeners around the fuselage shell. All but the two primary wing box frames are made of aluminum-alloy sections. The top part of each frame is formed from sheet and the lower part is machined from plate. The two wing box frames, FR36 and FR42, are machined from forgings. Clips, with cutouts for stringers, are riveted between the frames and the skin panels. The center fuselage is constructed of the following frames:
 -FR35. A full ring frame which makes the joint between the forward and center fuselage. The forward pressure limit bulkhead is installed in the lower part of this frame. The keel beam also connects to the bottom of the frame,
 -FR36. This is the forward primary frame of the wing-to-fuselage joint and is part of the wing box assembly. The frame is made of two forged sections which are machined and installed back-to-back. The longer of the two sections extends to STGR1; the shorter section extends to STGR18. The frame is connected to the wing-box front spar,
R  EFF : 001-049, 051-099, 101-149, 151-199, 53-31-00Page 6 201-299, 401-499, Aug 01/05
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 Center Fuselage - Frame and Skin Panel Location Figure 002A 
R  EFF :  151-199, 401-499,  53-31-00 Page 7 Aug 01/05
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 -FR37 thru FR41. Five frames which are connected to the left and right external attach points of the wing box root-ribs. These frames add to the structural strength of the center fuselage and emergency exit opening installed above the wing on each side,
 -FR42. This is the rear primary frame of the wing-to-fuselage joint and is part of the wing box assembly. The frame, almost the same as FR36, is two forged sections which are machined and installed back-to-back. The longer of the two sections extends to STGR1; the shorter section extends to STGR11. The frame is connected to the wing box rear spar,
 -FR43 thru FR45. These frames go around the shell and connect with the side box assemblies (left and right) and extend into the main landing-gear bay. Two slanting frames connect with the frame ends on each side to shape and strengthen the landing-gear wheel openings,
 -FR46. The rear pressure-limit bulkhead is installed in the lower part of this frame. The bulkhead completes the pressure limit zone of the center fuselage and makes the rear wall of the main landing-gear bay. The bulkhead slopes to the rear at the bottom to give the necessary wheel retraction area in the main landing-gear bay. The keel beam connects to the bottom of the frame,
 -FR47/51. A full ring frame which makes the joint between the center and rear fuselage sections.
 (2) Skin Panels (Ref. Fig. 002A) Five primary skin panels and four lower side panels make the center fuselage skin. The five primary panels extend the length of the center fuselage and include: - one top panel which extends across the width of the shell from
 STGR6 left to STGR6 right. The panel edges overlap the side panel edges and the panels are then riveted together,
 -two side panels, a top and middle on each side. The top side panel extends from STGR6 to STGR18 and includes nine passenger cabin windows and the emergency exit opening. The middle side panel includes the bottom part of the emergency exit opening. The panel extends from STGR18 and attaches to the wing root cruciform-fitting and forward and rear lower side panels. The top side panel lower edges overlap the middle side-panel edges and are then riveted together at STGR18. Both side panel edges have a recess so that their outer faces are in line with each other when riveted together. The top panel and the top and middle side panels are chemically milled. Stringers are riveted to them on the inner surface to make them stronger. Two lower side panels, a forward and a rear panel on each side, complete the center fuselage skin. They include:

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a forward lower side panel, left and right, installed in front of the wing center box between FR35 and FR36. Each panel, complete with stringers on the outer face, is chemically milled. The panel contains openings for systems interface between the fuselage and the wing leading edge. You can get access to both forward lower side panels from behind the belly fairing structure,

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a rear lower side-panel, left and right. The panels surround the wheel openings of the main landing-gear bay aft of the wing centerbox structure. They are installed between FR42 and FR47/51 and span between the middle side panel and keel beam structure. Two slanting frames (connected together at one end to make an inverted V-shape) support and strengthen each panel at the edges of the wheel opening. The panels are chemically milled and stringers are riveted on their outer face. You can get access to both rear lower side panels from behind the belly fairing structure.
　
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