Insertion Doubler Skin Insertion Skin Doubler$^{P}$ E Sealer Removed damage 0.35" 0.35" 0.50" - A A 0.58" 0.58" 0.10" rad. A A 0.064" 245-T4 Alclad$^{TM}$ strip Use AN470 or AN456 AD3 rivets Stringer CS-14 and CS-15 0.04" 245-T4 Alclad TM If damage has been cut away from center section of stringer length,  both ends of new portion must be attached as shown below. 3.35" 3.35" 0.90" 0.90" 0.40" 0.90" 0.90" 0.20" Original structure Repair parts Repair parts in  cross section Figure 4-182.  Pressurized skin repair.  Figure 4-183. Stringer repair. Spar Repair Longeron Repair 4-104 Most repairs to bulkheads are made from flat sheet stock if  spare parts are not available. When fabricating the repair from  flat sheet, remember the substitute material must provide  cross-sectional tensile, compressive, shear, and bearing  strength equal to the original material. Never substitute  material that is thinner or has a cross-sectional area less than  the original material. Curved repair parts made from flat sheet  must be in the “0” condition before forming, and then must  be heat treated before installation. Generally, longerons are comparatively heavy members  that serve approximately the same function as stringers.  Consequently, longeron repair is similar to stringer repair.  Because the longeron is a heavy member and more strength  is needed than with a stringer, heavy rivets are used in the  repair. Sometimes bolts are used to install a longeron repair,  due to the need for greater accuracy, they are not as suitable  as rivets. Also, bolts require more time for installation. If the longeron consists of a formed section and an extruded  angle section, consider each section separately. A longeron  repair is similar to a stringer repair, but keep the rivet pitch  between 4 and 6 rivet diameters. If bolts are used, drill the  bolt holes for a light drive fit. The spar is the main supporting member of the wing. Other  components may also have supporting members called spars  that serve the same function as the spar does in the wing.  Think of spars as the hub, or base, of the section in which they  are located, even though they are not in the center. The spar  is usually the first member located during the construction of  the section, and the other components are fastened directly  or indirectly to it. Because of the load the spar carries, it is  very important that particular care be taken when repairing  this member to ensure the original strength of the structure  is not impaired. The spar is constructed so that two general  classes of repairs, web repairs and cap strip repairs, are  usually necessary.