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chapter, various fabrics and treatment systems are discussed, as well as basic covering techniques. 

## Fabric Terms 

To facilitate the discussion of fabric coverings for aircraft, the following definitions are presented. Figure 3-2  illustrates some of these items. 

• Warp—the direction along the length of fabric. 

• Fill or weave—the direction across the width of the fabric. 

• Count—the number of threads per inch in warp or filling. 

• Ply—the number of yarns making up a thread. 

• Bias—a cut, fold, or seam made diagonally to the warp or fill threads. 

• Pinked edge—an edge which has been cut by machine or special pinking shears in a continuous series of Vs to prevent raveling. 

• Selvage edge—the edge of cloth, tape, or webbing woven to prevent raveling. 

• Greige—condition of polyester fabric upon completion of the production process before being heat shrunk. 

• Cross-coat—brushing or spraying where the second coat is applied 90° to the direction the first coat was applied. The two coats together make a single cross coat. [Figure 3-3] 

## Legal Aspects of Fabric Covering 

When a fabric-covered aircraft is certificated, the aircraft manufacturer uses materials and techniques to cover the aircraft that are approved under the type certificate issued for that aircraft. The same materials and techniques must be used by maintenance personnel when replacing the aircraft fabric. Descriptions of these materials and techniques are 

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in the manufacturer’s service manual. For example, aircraft originally manufactured with cotton fabric can only be re-covered with cotton fabric unless the Federal Aviation Administration (FAA) approves an exception. Approved exceptions for alternate fabric-covering materials and procedures are common. Since polyester fabric coverings deliver performance advantages, such as lighter weight, longer life, additional strength, and lower cost, many older aircraft originally manufactured with cotton fabric have received approved alteration authority and have been re- covered with polyester fabric. 

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