Aircraft manufacturers use different repair techniques and  repairs designed and approved for one type of aircraft are  not automatically approved for other types of aircraft. When  repairing a damaged component or part, consult the applicable  section of the manufacturer’s SRM for the aircraft. Usually  the SRM contains an illustration for a similar repair along  with a list of the types of material, rivets and rivet spacing,  and the methods and procedures to be used. Any additional  knowledge needed to make a repair is also detailed. If the  necessary information is not found in the SRM, attempt to  find a similar repair or assembly installed by the manufacturer  of the aircraft. When visually inspecting damage, remember that there may  be other kinds of damage than that caused by impact from  foreign objects or collision. A rough landing may overload one  of the landing gear, causing it to become sprung; this would  be classified as load damage. During inspection and sizing up  of the repair job, consider how far the damage caused by the  sprung shock strut extends to supporting structural members. Warped wings are usually indicated by the presence of  parallel skin wrinkles running diagonally across the wings  and extending over a major area. This condition may develop  from unusually violent maneuvers, extremely rough air, or  extra hard landings. While there may be no actual rupture of  any part of the structure, it may be distorted and weakened.  Similar failures may also occur in fuselages. Small cracks in  the skin covering may be caused by vibration and they are  frequently found leading away from rivets. Aluminum alloy surfaces having chipped protective coating,  scratches, or worn spots that expose the surface of the metal  should be recoated at once, as corrosion may develop rapidly.  The same principle is applied to aluminum clad (Alclad™)  surfaces. Scratches, which penetrate the pure aluminum  surface layer, permit corrosion to take place in the alloy  beneath. A shock occurring at one end of a member is transmitted  throughout its length; therefore, closely inspect all rivets,  bolts, and attaching structures along the complete member  for any evidence of damage. Make a close examination for  rivets that have partially failed and for holes that have been  elongated. Whether specific damage is suspected or not, an aircraft  structure must occasionally be inspected for structural  integrity. The following paragraphs provide general  guidelines for this inspection. A simple visual inspection cannot accurately determine if  suspected cracks in major structural members actually exist  or the full extent of the visible cracks. Eddy current and  ultrasonic inspection techniques are used to find hidden  damage. Types of damage and defects that may be observed on aircraft  parts are defined as follows: When inspecting the structure of an aircraft, it is very  important to watch for evidence of corrosion on the inside.  This is most likely to occur in pockets and corners where  moisture and salt spray may accumulate; therefore, drain  holes must always be kept clean. While an injury to the skin covering caused by impact with an  object is plainly evident, a defect, such as distortion or failure  of the substructure, may not be apparent until some evidence  develops on the surface, such as canted, buckled or wrinkled  covering, and loose rivets or working rivets. A working rivet  is one that has movement under structural stress, but has not  loosened to the extent that movement can be observed. This  situation can sometimes be noted by a dark, greasy residue or  deterioration of paint and primers around rivet heads. External  indications of internal injury must be watched for and correctly  interpreted. When found, an investigation of the substructure  in the vicinity should be made and corrective action taken. •  Cut—loss of metal, usually to an appreciable depth  over a relatively long and narrow area, by mechanical  •  Crack—a physical separation of two adjacent portions  of metal, evidenced by a fine or thin line across the  surface caused by excessive stress at that point. It  may extend inward from the surface from a few  thousandths of an inch to completely through the  section thickness. •  Corrosion—loss of metal from the surface by chemical  or electrochemical action. The corrosion products  generally are easily removed by mechanical means.  Iron rust is an example of corrosion. •  Burr—a small, thin section of metal extending beyond  a regular surface, usually located at a corner or on the  edge of a hole. •  Burnishing—polishing of one surface by sliding  contact with a smooth, harder surface. Usually there  is no displacement or removal of metal. •  Brinelling—occurrence of shallow, spherical  depressions in a surface, usually produced by a part  having a small radius in contact with the surface under  high load. Types of Damage and Defects Inspection of Damage  4-90