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Summary

The primary objective in aircraft repair is to restore the damaged part to its original condition. Each damaged part must be studied to determine if repair or replacement is required. All damage is not obvious or limited to an immediate location. A thorough assessment of a damaged area includes inspecting supporting structural members and adjacent rivets and bolts to see if they have sustained damage also. The assessment of damage also includes looking for weathering and corrosion. A white crystalline deposit at loose rivets and bolts, scratches, dents, and places where moisture can collect is corrosion.

A visual inspection does not reveal the existence or extent of cracks. Methods used to locate cracks and their extent include ultrasonic waves, X rays, Zy-glo, and penetrating dye. Because dye does not need expensive or complicated equipment, it is used in the field. The area to be dyed must be thoroughly cleaned. The dye is applied by brushing or swabbing and allowed to penetrate for 3 to 15 minutes. An even coat of developer is applied and allowed to dry. Defects are indicated in red and cracks show up as red lines. Scattered, unpatterned dots indicate porosity. All the materials used in the dye test are flammable, and prolonged breathing of the fumes is injurious.

Damages are classified as negligible, repairable by patching, repairable by insertion, and repairable by replacement. Availability of repair materials and time can influence the decision to repair or replace a part.

Corrosion is the process of a metal deteriorating by chemical reaction. Such deterioration is minimized by coating, plating, or painting metals subject to corrosion. Control of this process is necessary to protect aircraft operational integrity, limit expenses, and reduce maintenance manhours. Corrosion classifications are uniform etch effect, pitting, intergranular, exfoliation, galvanic, concentration cell, and stress corrosion cracking, and fatigue corrosion. Inspections for corrosion must be made at all periodic inspections.

The five stresses an aircraft is subject to are tension, compression, shear, bending, and torsion. The first three are called basic stresses and the others are called combination stresses. Bending, torsion, and shear are the most frequently encountered in airframe repair.

The prime requirement in repair material selection is to duplicate the structure's original strength. Caution must be used if alloys must be substituted, and the applicable technical manual must be consulted. New sections for repair or replacement must be made to the dimensions given in the appropriate technical manual. In addition, material must be marked with an aircraft marking pencil to prevent harmful scratches being made on the metal.

In general, the rivet size and alloy used in the repair must be the same as the original. For reworked enlarged or deformed rivet holes the next size rivet must be used. If blind rivets are used, the applicable technical manual must be consulted for type, size, number, spacing, and edge distance.

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