aircraft and the specific location of the damage on the aircraft. Class I Class II Class III Class IV Class V Class VI Class VII Cuts, scratches, pits, erosion or abrasions not exceeding 0.005 inch in depth and 5 inches in length. Damage with dents in the skin up to 3 inches in diameter and 0.01 inch in depth, with no delamination between skin plies, no cracks or graphite fiber breakage, or skin to honeycomb core separation. Delamination between plies, including the skin land area, opened up to external edge and up to 1 1/2 inches in diameter. Skin damage including delami- nation, cracks, cuts, scratches or skin erosion exceeding 0.015 inch in depth, but less than full penetration, with no damage to honeycomb core. Damage is single skin damage, including full penetration, accom- panied with honeycomb core damage. Damage to both skins, including full penetration, accompanied with honeycomb core damage. Damage is water trapped in honey- comb area. REPAIR CRITERIA Repair criteria differ in the same way that initial design requirements for aircraft differ. Criteria for a repair can be less demanding if the repair is considered to be temporary. Temporary repairs are performed for such requirements as a onetime flight to a repair facility or one more mission under combat conditions. However, most repairs are intended to be permanent, and, except for special conditions, criteria are applied so that the repair will remain acceptable for the life of the aircraft. One of the major factors that influences the repair quality is the environment where the repairs are to made. For example, the presence of moisture is critical to bonded repairs. Epoxy resins can absorb 1.5 to 2 times their weight in moisture, thereby reducing the ability of the resins to support the fibers. Dirt and dust can seriously affect bonded repairs. Oils, vapors, and solvents prevent good adhesion in bonded surfaces and can lead to voids or delamination. To perform quality repairs, personnel must have a knowledge of the composite system to be repaired, type of damage, damage limitations/ classifications, repair publications, materials, tools and equipment, and repair procedures. The repair facilities where the work is to be performed will be clean and climate controlled if possible. The relative humidity should be 25 percent to 60 percent and temperatures stable at 65° to 75°F. If repairs are to be made in an uncontrolled environment (hangar/flight deck), patches and adhesives will be prepared in a controlled environment and sealed in an airtight bag before being brought to the repair site. Strength Restoration Full strength repairs are desirable and should be made unless the cost is prohibitive or the facilities are inadequate. Less than full strength repairs are sometimes allowed on secondary structures that are lightly loaded, stiffness-critical structures designed for limited deflections rather than for carrying large loads (doors), or structures designed to a minimum thickness requirement for general resistance to handling damage (fuselage skins). Repair manuals for specific aircraft frequently “zone” the structure to show the amount of strength restoration needed or the kinds of standard repairs that are acceptable. Repair zones help to identify and classfy damage by limiting repairs to the load-carrying requirements. Repair zone borders indicate changes in load-carrying requirements due to changes in the structure, skin thickness, ply drop-offs, location of supporting members (ribs and spars), ply orientation, core density, size and type of materials. Damage in one zone may be repairable, where as the same type of damage in an adjacent zone may not be repairable. See figure 14-27. Aerodynamic Smoothness High-performance aircraft depend on smooth external surfaces to minimize drag. During initial fabrication, smoothness requirements are specified, usually by defining zones where different levels of aerodynamic smoothness are required. These most 14-26