After the extent of damage has been determined, it should be classified in one of the following categories: negligible damage, damage repairable by patching, damage repairable by insertion, or damage requiring replacement of parts. See figure 13-56. Before proceeding with the repair of the airframe, it is necessary that the applicable structural repair manual be consulted for the procedures and materials to be used. If the applicable manual is not available, the General Manual for Structural Repair, NA 01-1A-1, may be used. If any conflict should exist between the two manuals, the specific manual takes precedence.

NEGLIGIBLE DAMAGE. Negligible damage is that damage or distortion that may be allowed to exist as is or corrected by some simple procedure, such as removing dents, stop-drilling cracks, burnishing scratches or abrasions, without placing a restriction on the flight status of the aircraft. Before classifying damage as negligible, make sure the damage complies with the manufacturers specified limits of negligible damage.

DAMAGE REPAIRABLE BY PATCHING. Damage that can be repaired by installing a reinforcement or patch to bridge the damaged portion of a part may be classified as a damage repairable by patching. Reinforcement members are attached to the undamaged portions of the part to restore full load-carrying characteristics and airworthiness of the aircraft. Damage repairable by patching is specified for each member of the airframe.

DAMAGE REPAIRABLE BY INSERTION. Damage that is extensive enough to involve a major portion of a member, but which is not so extensive as to require replacement, is classified as damage repairable by insertion. The repair is made by inserting a new section and splicing it to the affected member.

DAMAGE REQUIRING REPLACEMENT. Damage that cannot be repaired by any practical means is classified as damage requiring replacement. Short structural members usually must be replaced because repair of such members is generally impractical.

Damage repair procedures vary greatly from aircraft to aircraft and the type of repair that is going to be performed. Also consult the applicable aircraft MIMs and the applicable aircraft structural repair manual before performing any structural repairs.

The major requirement in making a repair is the duplication of strength of the original structure. You should consult the structural repair manual for the aircraft concerned for the alloy thickness and temper designation of the repair material to be used. This manual will also designate the type and spacing of rivets or fasteners to be used in the repair.

In some instances, substitutions of materials are allowed. When you are making a substitution of materials and conflicting information between manuals exists, the structural repair manual for the aircraft being repaired should be used.

Figure 13-56.Classification of damages.

You have several steps to take to find the correct repair materials and procedures in a structural repair manual. Figure 13-57 shows each of the steps.

NOTE: The aircraft structural repair manual, shown in figure 13-57, was selected as a typical manual. The procedures that follow are typical but are not standard. Various manufacturers use different methods to indicate the types of materials used and special instructions for using their particular manual.

1. The extent of the damage to the aircraft is determined by the inspection of the damaged area, as previously explained.

2. Using a master index diagram, identify the damaged group of the aircraft. From the table shown on the diagram, determine the section of the manual where the component is found.

3. After locating the correct group master index diagram, obtain the correct item number for the damaged component from the illustration.

4. Find the index number for the damaged unit from the component diagram.

5. The index number is (hen matched with the item number on the repair material chart. This chart will normally give the parts description, drawing number, gauge, type of material, and location of repair diagram.

6. You can find the repair diagram by locating the required section of the manual and turning to the correct figure in that section. Access provisions and negligible damage information are given on the repair diagrams. After the damage has been cleaned, determine whether or not the damage is negligible according to the repair diagram. If the damage is within the limits of negligible damage, it may be disregarded unless it is necessary to close the hole for aerodynamic smoothness. If the damage exceeds the limits of negligible damage, it must be repaired according to the repair diagram or replaced.