It is required to have an IA involved in the process of re- covering a fabric aircraft because re-covering is a major repair  or major alteration. Signatures are required on FAA Form  337 and in the aircraft logbook. To ensure work progresses  as required, the IA should be involved from the beginning,  as well as at various stages throughout the process.  This section describes steps common to various STC and  manufacturer covering processes, as well as the differences  of some processes. To aid in proper performance of fabric  covering and repair procedures, STC holders produce  illustrated, step-by-step instructional manuals and videos that  demonstrate the correct covering procedures. These training  aids are invaluable to the inexperienced technician. Since modern fabric coverings last indefinitely, a rare  opportunity to inspect the aircraft exists during the re- covering process. Inspectors and owner-operators should  use this opportunity to perform a thorough inspection of the  aircraft before new fabric is installed. made and fabric is cut and stitched so that each major surface,  including the fuselage and wings, can be covered with a single,  close-fitting envelope. Since envelopes are cut to fit, they are  slid into position, oriented with the seams in the proper place,  and attached with adhesive to the airframe. Envelope seams  are usually located over airframe structure in inconspicuous  places, such as the trailing edge structures and the very top and  bottom of the fuselage, depending on airframe construction.  Follow the manufacturer’s or STC’s instructions for proper  location of the sewn seams of the envelope when using this  method.  [Figure 3-13] The method of fabric attachment should be identical, as far as  strength and reliability are concerned, to the method used by  the manufacturer of the aircraft being recovered or repaired.  Carefully remove the old fabric from the airframe, noting the  location of inspection covers, drain grommets, and method  of attachment. Either the envelope method or blanket method  of fabric covering is acceptable, but a choice must be made  prior to beginning the re-covering process.  In the blanket method of re-covering, multiple flat sections  of fabric are trimmed and attached to the airframe. Certified  greige polyester fabric for covering an aircraft can be up to  70 inches in width and used as it comes off the bolt. Each  aircraft must be considered individually to determine the  size and layout of blankets needed to cover it. A single  blanket cut for each small surface (i.e., stabilizers and control  surfaces) is common. Wings may require two blankets that  overlap. Fuselages are covered with multiple blankets that  span between major structural members, often with a single  blanket for the bottom. Very large wings may require more  than two blankets of fabric to cover the entire top and bottom  surfaces. In all cases, the fabric is adhered to the airframe  using the approved adhesives, following specific rules for the  covering process being employed.  [Figure 3-12] Proper preparation for re-covering a fabric aircraft is  essential. First, assemble the materials and tools required to  complete the job. The holder of the STC usually supplies a  materials and tools list either separately or in the STC manual.  Control of temperature, humidity, and ventilation is needed  in the work environment. If ideal environmental conditions  cannot be met, additives are available that compensate for  this for most re-covering products.  An alternative method of re-covering, the envelope method,  saves time by using precut and pre-sewn envelopes of fabric to  cover the aircraft. The envelopes must be sewn with approved  machine sewing thread, edge distance, fabric fold, etc., such  as those specified in AC 43.13-1 or an STC. Patterns are  Figure 3-13.  A custom-fit presewn fabric envelope is slid into  position over a fuselage for the envelope method of fabric covering.  Other than fitting, most steps in the covering process are the same  as with the blanket covering method. Figure 3-12.  Laying out fabric during a blanket method re-covering  job. Preparation for Fabric Covering Work Blanket Method vs. Envelope Method  General Fabric Covering Process 3-12