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9/8/98 AC 43.13-1B SECTION 4. WINDSHIELDS, ENCLOSURES, AND WINDOWS 3-40. GENERAL. These repairs are appli cable to plastic windshields, enclosures, and windows in nonpressurized airplanes. For pressurized airplanes, replace or repair plastic elements in accordance with the manufac turer’s recommendation. When windshields and side windows made of acrylic plastics are damaged, they are usually replaced unless the damage is minor and a repair would not be in the line of vision. Repairs usually require a great deal of labor. Replacement parts are readily available, so replacement is normally more economical than repair. a. Minor Repairs. There are times, how ever, when a windshield may be cracked and safety is not impaired. In that case, repairs can be made by stop-drilling the ends of the crack with a # 30 drill (1/8 inch) to prevent the con centration of stresses causing the crack to con tinue. Drill a series of number 40 holes a half-inch from the edge of the crack about a half-inch apart, and lace through these holes with brass safety wire (see figure 3-24) and seal with clear silicone to waterproof. b. Temporary Repairs. One way to make a temporary repair is to stop-drill the ends of the crack, and then drill number 27 holes every inch or so in the crack. Use AN515-6 screws and AN365-632 nuts with AN960-6 washers on both sides of the plastic. This will hold the crack together and prevent further breakage until the windshield can be properly repaired or replaced. (See fig ure 3-24.) c. Permanent Repairs. Windshields or side windows with small cracks that affect only the appearance rather than the airworthi ness of a sheet, may be repaired by first stop-drilling the ends of the crack with a # 30 or a 1/8-inch drill. Then use a hypoder mic syringe and needle to fill the crack with polymerizable cement such as PS-30 or Weld-On 40, and allow capillary action to fill the crack completely. Soak the end of a 1/8-inch acrylic rod in cement to form a cush ion and insert it in the stop-drilled hole. Allow the repair to dry for about 30 minutes, and then trim the rod off flush with the sheet. d. Polishing and Finishing. Scratches and repair marks, within certain limitations, can be removed from acrylic plastic. No sanding that could adversely affect the plas tic’s optical properties and distort the pilot’s vision should be done on any portion of a windshield. (1) If there are scratches or repair marks in an area that can be sanded, they may be re moved by first sanding the area. Use 320- or 400-grit abrasive paper that is wrapped around a felt or rubber pad. (2) Use circular rubbing motions, light pressure, and a mild liquid soap solution as a lubricant. After the sanding is complete, rinse the surface thoroughly with running water. Then, using a 500-grit paper, continue to sand lightly. Keep moving to higher grit paper and sand and rinse until all of the sanding or repair marks have been removed. (3) After using the finest abrasive pa per, use rubbing compound and buff in a cir cular motion to remove all traces of the sand ing. e. Cleaning. Acrylic windshields and windows may be cleaned by washing them with mild soap and running water. Rub the surface with your bare hands in a stream of water. Follow with the same procedure but with soap and water. After the soap and dirt have been flushed away, dry the surface with a soft, clean cloth or tissue and polish it with a Par 3-40 Page 3-23PDF Image | AFS-640
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