Normally, the rivet size and material should be the same as  the original rivets in the part being repaired. If a rivet hole has  been enlarged or deformed, the next larger size rivet must be  used after reworking the hole. When this is done, the proper  edge distance for the larger rivet must be maintained. Where  access to the inside of the structure is impossible and blind  rivets must be used in making the repair, always consult the  applicable aircraft maintenance manual for the recommended  type, size, spacing, and number of rivets needed to replace  either the original installed rivets or those that are required  for the type of repair being performed. The rivet pattern for a repair must conform to instructions  in the applicable aircraft manual. The existing rivet pattern  is used whenever possible. Prior to assembly of repair or replacement parts, make certain  that all existing corrosion has been removed in the area and  that the parts are properly insulated one from the other. Once the need for an aircraft repair has been established, Title  14 of the Code of Federal Regulations (14 CFR) defines the  approval process. 14 CFR part 43, section 43.13(a) states that  each person performing maintenance, alteration, or preventive  maintenance on an aircraft, engine, propeller, or appliance  shall use the methods, techniques, and practices prescribed in  the current manufacturer’s maintenance manual or instructions  for continued airworthiness prepared by its manufacturer, or  other methods, techniques, or practices acceptable to the  Administrator. AC 43.13-1 contains methods, techniques, and  practices acceptable to the Administrator for the inspection  and repair of nonpressurized areas of civil aircraft, only when  there are no manufacturer repair or maintenance instructions.  This data generally pertains to minor repairs. The repairs  identified in this AC may only be used as a basis for FAA  approval for major repairs. The repair data may also be used  as approved data, and the AC chapter, page, and paragraph  listed in block 8 of FAA Form 337 when: Engineering support from the aircraft manufacturer is  required for repair techniques and methods that are not  described in the aircraft maintenance manual or SRM.  FAA Form 337, Major Repair and Alteration, must be  completed for repairs to the following parts of an airframe and  repairs of the following types involving the strengthening,  reinforcing, splicing, and manufacturing of primary structural  members or their replacement, when replacement is by  fabrication, such as riveting or welding.  [Figure 4-173] For major repairs made in accordance with a manual or  specifications acceptable to the Administrator, a certificated  repair station may use the customer’s work order upon which  the repair is recorded in place of the FAA Form 337. In aircraft construction, stressed skin is a form of construction  in which the external covering (skin) of an aircraft carries  part or all of the main loads. Stressed skin is made from high  strength rolled aluminum sheets. Stressed skin carries a large  portion of the load imposed upon an aircraft structure. Various  specific skin areas are classified as highly critical, semicritical,  Repair of Stressed Skin Structure  a. The user has determined that it is appropriate to the  product being repaired; b. It is directly applicable to the repair being made; and c. It is not contrary to manufacturer’s data. •  Repair of three or more adjacent wing or control  surface ribs or the leading edge of wings and control  surfaces between such adjacent ribs •  Splicing of thin sheets •  Box beams •  Monocoque or semimonocoque wings or  control surfaces •  Wing stringers or chord members • Spars •  Spar flanges •  Members of truss-type beams •  Thin sheet webs of beams •  Keel and chine members of boat hulls or floats •  Wing main ribs and compression members •  Corrugated sheet compression members that act as  flange material of wings or tail surfaces •  Wing or tail surface brace struts, fuselage longerons •  Members of the side truss, horizontal truss,  or bulkheads •  Main seat support braces and brackets •  Landing gear brace struts •  Repairs involving the substitution of material •  Repair of damaged areas in metal or plywood stressed  covering exceeding six inches in any direction •  Repair of portions of skin sheets by making  additional seams Rivet Spacing and Edge Distance Corrosion Treatment  Approval of Repair 4-94 Rivet Selection 