SCRAP—To discard, with proper authori- zation, items, parts or materials that are obsolete or no longer usable. SDLM—Standard depot-level maintenance. Provides for a comprehensive inspection of selected aircraft structures and materials, critical defect correction, preventive maintenance as required, modification and technical directive compliance to ensure reliability and operational availability of the aircraft at minimum cost for the established operating service period, and to provide intermediate support during the total service life. SDLM/CONVERSION—Standard depot- level rework concurrent with special rework, the accomplishment of which alters the basic charac- teristics of the aircraft to such an extent as to effect a change in any part of the model designation (i.e.,    F-4B to F-4D). NAVAIR approval required. SDLM/CRASH DAMAGE—In addition to accomplishing SDLM (standard depot-level main- tenance), repair and restoration to a serviceable condition that part of the aircraft that has sustained damage resulting from an accident or an incident. SDLM/MODIFICATION—Accomplishment of standard depot-level rework concurrent with a modification that causes major work effort resulting from the installation of these technical directives. NAVAIR approval required. SEAM—A series of stitches joining two or more pieces of cloth. For government work, the type of seam is indicated by a symbol that gives the class of seam, the number of stitching, and the number of rows of stitching. (Reference Fed. Std. 751.) SEAM, DIAGONAL—A French-fell seam of the canopy that joins two sections of a gore. Diagonal seams meet the centerline of the gore at angles of 450 and 135. SEAM, ENGLISH-FELL—A seam in which one piece of cloth is folded back upon itself, and the other piece is a plain overlap. SEAM, FOUR-NEEDLE FOUR-STITCH— A method of stitching that can be performed in one operation by a four-needle sewing machine. It is used in sewing the vent hem, skirt hem, and radial seams of a canopy. SEAM, FRENCH-FELL—A seam in which the cloth is folded back upon itself and stitched. SEAM, OVERLAP—A seam in which the two pieces of cloth are joined by overlapping enough to accommodate one or more rows of stitching. SEAM, RADIAL—A seam, joining two gores, that extends radially from the vent to the skirt hem. SEAM, TWO-NEEDLE TWO-STITCH—A seam in one operation by a two-needle sewing machine; for example, a diagonal seam. SEAR—To melt or seal with heat; for example, to sear the end of nylon webbing, one heats the end until the nylon melts and fuses. This prevents raveling. Also, the catch that holds the hammer of a firing mechanism cocked. The sear in an automatic parachute ripcord release is attached to the aneroid in the receiver assembly. SEAT PAN—A sponge-rubber-covered metal seat that is contoured for comfort to the user. A seat pan is used with seat-type parachutes and back-type parachutes when a packaged life raft assembly is used. A high-speed seat pan has sections for support under the pilot’s thighs during ejection. This reduces leg strain caused by high acceleration loads. SECTION—Each major part of a gore. Sections are bordered by radial seams, diagonal seams, or vent or skirt hems. In the 28-foot, flat canopy, four sections are used in each gore (previously known as panel). SECURITY—An item firmly, positively, and safely attached in the authorized manner. SELVAGE—An edge of a woven fabric so formed as to prevent raveling, as compared to a cut edge, which will ravel. SELVAGE, BROKEN—Cut, broken, or tom selvage edge. SELVAGE, STRINGY OR LOOPY—Ir- regular stringy or loopy selvage edge. AI-13