(5) Repair of life rafts. When leaks due to tears, abrasions, or punctures are found, repairs should be made in accordcance with the recommendations of the manufacturer. Partially torn away supporting patches on the tube should be recemented so as to restore the raft to its airworthy condition. Mildewed or weak lanyards should be replaced, particularly those by which the CO, bottle is operated. This applies also to the line used to attach the raft to the airplane. All metal parts should be checked for corrosion; cleaned, or repaired if found to be defective. If leaky mattress valves Chave been found, they should be replaced. (6) Rating. Ratings of military rafts when used in civil aircraft are shown in the following table. Ratings of the 10-, 15-, and 20-man circular rafts built for civil use are stamped on the rafts by the manufacturer. NOTE: Rafts more than 5 years old are likely to be unairworthy due to deterioration. (e) Parachutes. With reasonable care, parachutes should last at least 5 years. They should not be carelessly tossed about, left in the airplanes so that they may become wet, or left in open places where they may be tampered with. They should not be placed where they may fall on oily floors or be subject to acid fumes from adjacent battery chargers. When repacking is done as required in Part 43 of the Civil Air Regulations, a careful inspection of the parachute should be made by a qualified parachute technician (rigger). If repairs or replacement of parts are necessary to maintain the airworthiness of the parachute assembly, such work should be done by the original parachute manufacturer or by qualified parachute technicians certificated in accordance with Part 25 of this subchapter, Parachute Technician's Certificates or by agencies qualified in ac cordance with Part 54 of this subchapter, Parachute Loft Certificates and Ratings. (f) Safety belts. (1) The Civil Air Regulations require that when safety belts are to be installed in aircraft after July 1, 1951, such belts must conform to standards established by the Federal Aviation Agency. These standards are contained in Technical Standard Order TSO-C22. Safety belts eligible for installation in aircraft may be identified by the marking TSO-C22 on the belt or by a military designation number since military belts comply with the strength requirements of the TSO. Airworthy type certificated safety belts currently in aircraft may be removed for cleaning and reinstalled. However, when a type certificated safety belt is found unairworthy it must be replaced with a TSOC22 or a new military belt. (2) The webbing of safety belts, even when mildew proofed, is subject to deterioration due to constant use, cleaning and the effects of aging. The clamping action of the serrations of the commonly used buckle also causes a reduction in strength of the webbing and fraying occurs after long periods of usage. Fraying of belts is an indication of wear and such belts are likely to be unairworthy because they can no longer hold the minimum required tensile load. Differences of opinion as to the airworthiness of a belt can be settled by testing a questionable belt to demonstrate that it will support the required load but such testing usually costs more than a new belt and in addition affects the belt so that it is not as strong after the test as it was before. Airworthy 1-person type certificated belts should be able to withstand a tensile load of 525 pounds and TSO belts should withstand the rated tensile load indicated on the belt label. Most 1-person TSO belts are rated for 1,500 pounds. For 2-person belts the loads should be doubled. (3) Since type certificated belts will not afford the crash protection provided by a TSO or military belt, such type certificated belts should not be repaired nor should their buckles or end fittings be reused on safety belts. If replacement of webbing or hardware of TSO or military belts is attempted, parts of identical design and material should be used. The stitch pattern should at least be identical to the original and the number of stitches per inch should be equal to the number used in the original belt. There is no objection to having a greater total length of stitching provided one line of stitches is not placed over another line. Lines of stitching should be at least three-sixteenths inch apart. A record should be kept, preferably in the log book, stating the extent to which the belt was repaired and the date. The original identification marking on the belt, conforming either to that required by TSO-C22, to a deviation from this marking, or to the military designation should be retained. Operators of a fleet of airplanes should follow the above suggestions, but keeping of records of renovations in a log book is impractical since the belts are never associated with any one particular airplane for any length of time. Therefore, in addition to retaining the original identification label and attaching it to the renovated belt, some additional simple marking should be used to indicate that the belt had been renovated. The date of renovation should also be shown. The use of the letter "R" followed by the date would be acceptable. This marking could be in the form of an indelibile ink stamping or cloth label stitched to the webbing. (g) Fire extinguishers. Inspection and maintenance of fire extinguishers should be in accordance with the manufacturer's instructions attached to the extinguisher unit. In connection with carbon tetrachloride extinguishers, owners who desire to refill their own units are cautioned not to refill them with commercial carbon tetrachloride inasmuch as it invariably contains a small percentage of water which ultimately causes corrosion of the moving parts of the extinguisher mechanism. Carbon tetrachloride for refilling fire extinguishers is sold in containers identifying the contents as being intended for such usage. (h) Radio equipment. For information pertaining to alterations and testing of radio equipment, see §§ 18.30-20 and 18.30-21. [Supp. 1, 18 F. R. 7391, Nov. 21, 1953, as amended by Supp. 5, 20 F. R. 7535, Oct. 8. 1955] § 18.30-10 Windshields and enclosures (FAA policies which apply to § 18.30). These repairs are applicable to plastic windshields, enclosures, and windows in non-pressurized airplanes. For pressurized airplanes the plastic elements should be replaced or repaired only in accordance with the manufacturer's recommendations. (a) Types of plastics. Two types of plastics are commonly used in transparent enclosures of aircraft. These materials are known as acrylic plastics and cellulose acetate plastics. (1) Replacement panels. Replacement panels should always be of material equivalent to that originally used by the manufacturer of the aircraft. There are many types of transparent plastics on the market. Their properties vary greatly, particularly in regard to expansion characteristics, brittleness under low temperatures, resistance to discoloration when exposed to sunlight, surface checking, etc. These properties have been considered by aircraft manufacturers in selecting materials to be used in their designs and the use of substitutes having different characteristics may result in subsequent difficulties. (b) Installation procedures for acrylic plastics. In installing a replacement panel, the same mounting method used by the manufacturer of the airplane should be followed. While the actual installation will vary from one type of aircraft to another, the following major principles should be considered in installing any replacement panels. (1) Never force an acrylic plastic panel out of shape to make it fit a frame. If a replacement panel does not fit easily into the mounting, a new replacement should be obtained or the whole panel heated and reformed. When possible, a new panel should be cut and fitted at ordinary room temperature. (2) In clamping or bolting acrylic plastic panels into their mountings, do not place the plastic under excessive compressive stress. It is easy to develop more than 1,000 pounds per square inch on the plastic by drawing up a nut and bolt good and tight. Each nut should be tightened to a firm fit then backed off one full turn. (3) (i) In bolt installations, spacers, collars, shoulders, or stop-nuts should be used to prevent tightening the bolt excessively. Whenever such devices are used by the airplane manufacturer they should be retained in the replacement installation. It is important that the original number of bolts, complete with washers, spacers, etc., be used. (ii) When rivets are used, adequate spacers or other satisfactory means to - prevent excessive tightening of the frame to the plastic should be provided. (4) Acrylic plastic panels should be -mounted between rubber, cork, or other gaskets to make the installation waterproof, to reduce vibration, and to help to distribute compressive stresses on the plastic. (5) Acrylic plastics expand and contract approximately three times as much as the metal channels in which they are mounted. Therefore, suitable allowance for dimensional changes with tempera-ture should be made. Clearances of - one-eighth-inch minimum should be allowed around the edges of small panels and larger clearances around the edges of large panels. (6) In installations involving bolts or ■rivets, the holes through the plastic should be oversize by one-eighth-inch diameter and centered so that the plastic = will not bind or crack at the edge of the holes. The use of slotted holes is also recommended. (7) Panels should be mounted to a suf=ficient depth in the channel to prevent falling out when it contracts at extremely low temperatures or when the panel is flexed. When the manufacturer's original design permits, panels up to 12 inches long should be mounted to a minimum depth of 1% inches. (c) Installation procedure for cellulose acetate plastics. In general the methods used for installation of cellulose acetate plastics are similar to those used for acrylic plastics. The coefficient of expansion of cellulose acetate exceeds that of acrylic resins. Also, the cellulose acetate plastics are affected by moisture and will change dimensionally as they absorb water. Therefore, allowance should be made in mounting this type plastic if wide variations in temperature and humidity are to be encountered. As a general rule an allowance of about one-eighth-inch per foot of panel length should be made for expansion and three-sixteenths-inch per foot for contraction. (d) Repair of plastics. Extensively damaged transparent plastic should be replaced rather than repaired whenever possible since even a carefully patched part is not the equal of a new section, either optically or structurally. At the first sign of crack development, a hole of one-eighth to three-sixteenths of an inch in diameter should be drilled at the extreme ends of the cracks as shown in figure 10-1. This serves to localize the cracks and to prevent further splitting by distributing the strain over a large area. If the cracks are small, stopping them with drilled holes will usually suffice until replacement or more permanent repair can be made. The following repairs are permissible; however, they should not be located in the line of the pilot's vision in normal flight and landing. (1) Surface patch. If a surface patch is to be installed, trim away the damaged area and round all corners. A piece of plastic of sufficient size to cover the damaged area and extend at least threefourths of an inch on each side of the crack or hole should be cut and the edges beveled as shown in figure 10-2. If the section to be repaired is curved, the patch should be fitted to the same contour by heating it in an oil bath at a temperature of 248° to 302° F. or it may be heated on a hot plate until soft. Boiling water should not be used for heating. The patch should be coated evenly with plastic solvent adhesive and placed immediately over the hole. A uniform pressure of from 5 to 10 pounds per square inch should be maintained on the patch for a minimum of 3 hours. The patch should be allowed to dry 24 to 36 hours before sanding or polishing is attempted. (2) Plug patch. In using inserted patches to repair holes in plastic structures, the holes should be trimmed to a perfect circle or oval and the edges beveled slightly. The patch should be slightly thicker than the material being repaired and should have similarly beveled edges. Patches should be installed in accordance with figure 10-3. The plug is heated until soft and pressed into the hole without cement, and allowed to cool, making a perfect fit. The plug should be removed, the edges coated with adhesive and then reinserted in the hole. A firm light pressure should be maintained until the cement has set. Sand or file the edges level with the surface, buff and polish. (e) Cleaning and polishing transparent plastic. (1) Plastics have many advantages over glass for aircraft use, but they lack the surface hardness of glass and care must be exercised while servicing the aircraft to avoid scratching or otherwise damaging the surface. (2) Plastic should be cleaned by washing with plenty of water and mild soap, using a clean, soft, grit-free cloth, sponge, or bare hands. Do not use gasoline, alcohol, benzene, actone, carbon tetrachloride, fire extinguisher or deicing fluids, lacquer thinners, or window cleaning sprays because they will soften the plastic and cause crazing. The plastic should not be rubbed with a dry cloth since this is likely to cause scratches and also build up an electrostatic charge which attracts dust particles to the surface. If after removing dirt and grease, no great amount of scratching is visible, the plastic should be finished with a good grade of commercial wax. The wax should be applied in a thin even coat and brought to a high polish by rubbing lightly with a soft cloth. (3) If, after removing dirt and grease, the surface is found marred by scratches, hand polish or buff out the scratches. Hand-polishing or buffing should not be attempted until the surface is clean. A soft, open-type cotton or flannel buffing wheel is suggested. Minor scratches may be removed by vigorously rubbing the affected area by hand or with a soft, clean cloth dampened with a mixture of turpentine and chalk or an automobile cleanser applied with a damp cloth. Remove the cleanser and polish with a soft, dry cloth. Acrylic and cellulose acetate plastics are thermoplastic and friction created by buffing or polishing too long in one spot can generate sufficient heat to soften the surface. This will produce visual distortion and should be guarded against. § 18.30-11 Hydraulic systems (FAA policies which apply to § 18.30). Airplane hydraulic systems should be maintained, serviced, and adjusted in accordance with manufacturer's maintenance manuals and pertinent component maintenance manuals. Certain general principles of maintenance and repair which apply are outlined below. (a) Hydraulic lines and fittings. All lines and fittings should be carefully inspected at regular intervals to insure airworthiness. Metal lines should be checked for leaks, loose anchorages, scratches, kinks, or other damage. Flexible hose lines should be checked for leaks, cuts, abrasions, soft spots, or other deterioration or damage. Fittings and connections should be inspected for leakage, looseness, cracks, burrs, or other damage. Defective elements should be replaced but may sometimes be repaired. Soft (1) Replacement of metal lines. When inspection shows a line to be damaged or defective, the entire line should be replaced. However, if the damaged section is localized, a repair section may be inserted. In replacing lines, always use tubing of the same size and material as the original line. Use the old tubing as a template in bending the new line, unless it is too greatly damaged, in which case a template can be made from soft iron wire. aluminum tubing (2SO, 3SO, or 52SO) under one-fourth inch outside diameter may be bent by hand. For all other tubing, an acceptable tube bending, hand or power, tool should be used. Bending should be done carefully to avoid excessive flattening, kinking, or wrinkling. Minimum bend radii should conform to the values shown in table 11-1. A small amount of flattening in bends is acceptable but should not exceed an amount such that the small diameter of the flattened portion is less than 75 percent of the original outside diameter. When installing the replacement tubing it should line up correctly with the mating part and should not be forced into line by means of the coupling nuts. (2) Tube connections. Most tubing connections are made using flared tube ends, and standard connection fittings: AN-818 nut and AN-819 sleeve. In forming flares, the tube ends must be cut square, filed smooth, have all burrs and sharp edges removed and be thoroughly cleaned. The tubing is then flared using the correct forming tools for the sizes of tubing and type of fitting. A double flare is used on soft aluminum tubing three-eighths inch outside diameter and under, and a single flare on all other tubing. In making the connections hydraulic fluid only should be used as a lubricant. The connection should then be tightened as overtightening will damage the tube or fitting, and may cause failure, and undertightening may cause leakage. (3) Repair of metal tube lines. (1) Minor dents and scratches in tubing may be repaired. Scratches or nicks no deeper than 10 percent of the wall thickness in aluminum alloy tubing only, not in the heel of a bend, may be repaired by burnishing with hand tools. Severe die marks, seams or splits in the tube should not be repaired; such lines should be re 1. Any crack or deformity in a s also unacceptable and should be ed. A dent less than 20 percent of the iameter is not objectionable unless n the heel of a bend. Dents may noved by drawing a bullet of proper hrough the tube by means of a of cable. A severely damaged line may be ed, if it is not desired to replace the line, by cutting out the damaged n and inserting a repair section ting of a short section of flared , flaring both ends of the undamtube remaining, and connecting tandard unions, sleeves, and tube If the damaged portion is short h, the insert tubing may be omitted ne repair made with one union and ets of connection fittings. Replacement of flexible lines. hen replacement of flexible hose s necessary, use the same type, size ength hose as the replaced line. è hose is of the swaged-end type, tire assembly should be obtained è correct size for replacement. If of the collet, or sleeve, quick-atole-end type, the assembly should de up in accordance with the manrer's directions, using the pred tools, so that the replacement bly is of the same size and length as placed line. The hose should be inI without twisting by keeping the line on hose straight. Use only ulic fluid for lubricating threads. A hose should never be stretched between two fittings as this will in overstressing and failure at the nder pressure. The length of hose I be sufficient to provide about 5 to ent slack. in and component manufacturer's structions should be carefully followed. Hydraulic filter elements should be inspected at frequent intervals and replaced as necessary. § 18.30-12 Electrical systems (FAA policies which apply to § 18.30). (a) General. All electric equipment, electric assemblies, and wiring installations should be frequently inspected for damage, general condition, and proper functioning to assure the continued satisfactory operation of the electric system. The adjustment, repair, overhaul, and testing of all electric equipment and systems should be accomplished in accordance with the recommendations and procedures set forth in Maintenance Instructions, or manuals published by the Aircraft and Equipment Manufacturers. (b) Inspection and operating checking. Frequent visual inspections, operating checks of all electric circuits and equipment, and replacement or repair when deficiencies are found are effective in minimizing electrical troubles and hazards in airplanes. A suggested list of items to look for during these inspections and the checks to be performed are itemized below: Damaged or overheated equipment, connections and wiring or worn wiring insulation. Excessive resistance at high current carrying connections, as determined by millivolt drop test. Alinement of electrically driven equip ment. Poor electric bonding. Cleanliness of equipment and connections. Proper support of wiring and conduit, and satisfactory attachment to the structure. Tightness of connections, terminals and ferrules. Continuity of fuses, operation of circuit breakers. Condition of electric lamps. Clearance or insulation of exposed terminals. Adequacy of safety wire, cotter pins, etc. Operational check of electrically operated equipment such as motors, inverters, generators, batteries, lights, etc. Voltage check of electric system operation with portable precision voltmeter. (1) Cleaning and preservation. Frequent cleaning of electric equipment to remove dust, dirt, and grime is recommended. Fine emery cloth may be used to clean terminals and mating surfaces if they appear corroded or dirty. Crocus cloth or very fine sandpaper should be |