3.13-1A Clad aluminum alloys have surface layers of e aluminum or corrosion-resistant alumin alloy bonded to the core material to inpit corrosion. Presence of such a coating may determined under a magnifying glass by exination of the edge surface which will show ree distinct layers.
b. Test for Distinguishing Heat-Treatable and inheat-Treatable Aluminum Alloys. If for any ason the identification mark of the alloy is t on the material, it is possible to distinguish tween some heat-treatable alloys and some nheat-treatable alloys by immersing a same of the material in a 10 percent solution of ustic soda (sodium hydroxide). Those heateated alloys containing several percent of ap 7 Page 131 copper (2014, 2017, and 2024) will turn black due to the copper content. High copper alloys when clad will not turn black on the surface, but the edges will turn black at the center of the sheet where the core is exposed. If the alloy does not turn black in the caustic soda solution it is not evidence that the alloy is not heat-treatable, as various high strength heattreatable alloys are not based primarily on the use of copper as an alloying agent. These include among others 6058, 6061, and 7075 alloys. The composition and heat-treatability of alloys which do not turn black in a caustic soda solution can be established only by chemical or spectro-analysis.
268.-278. RESERVED.
Par 267
Page 132 AC 43.
Section 2. TESTING OF METALS
279. HARDNESS TESTING. Hardness testing provides a convenient means for determining, within reasonable limits, the tensile strength of steel. It has several limitations in that it is not suitable for very soft or very hard steels.
In hardness testing, the thickness of the specimen being tested and the edge distance should be such that distortion of the metal due to these factors is eliminated. Several readings should be taken and the results averaged. In general, the higher the tensile strength, the greater is its hardness. Common methods of hardness testing are outlined in the following paragraphs. These tests are suitable for determining the tensile properties resulting from the heat treatment of steel. Care should be taken to have case hardened, corroded, pitted, decarburized, or otherwise nonuniform surfaces removed to a sufficient depth. Also, exercise caution not to cold-work and consequently harden the steel during removal of the surface.
The relationship between tensile strength and hardness is indicated in figure 7.3.
282. VICKERS HARDNESS TEST. In this test small pyramidal diamond is pressed into metal. The hardness number is the ratio of load to the surface area of indentation.
283. TESTING ALUMINUM. Hardness tests :
useful for testing aluminum alloy chiefly a means of distinguishing between anneal cold-worked, heat-treated, and heat-trea and aged material. It is of little value in in cating the strength or quality of heat tre ment. Typical hardness values for alumin alloys are shown in figure 7.4 FIGURE 7.4.-Hardness values for aluminum alloy!
Brinell numb Material commercial Eardnesa 500 kg. lom designation temper 10 mm. ball 1100 A18 8008 H16
280. BRINELL HARDNESS TEST. In this test a 2014 standard load is applied to a smooth surface of T8 185 2017 45 metal through a hardened steel ball, one centi- 18 105 meter in diameter. The numerical value of Bri- 2024 47 nell hardness is equal to the load divided by T· 120 the surface area of the resulting spherical im- 2025 T8 110 pression. 8151 100 5052 47 H86 78
281. ROCKWELL HARDNESS TEST. In this test, a 6061 80 standard minor load is applied to seat a hard- 65 ened steel ball or a diamond cone in the surface 95 of the metal, followed by the application of a 7075 185 standard major load. The hardness is meas- 7079 185 T6 185 75 ured by depth of penetration. Rockwell super- 220 T4 ficial hardness tests are made using light 0855 T6 minor and major loads and a more sensitive A856 system for measuring depth of indentation. It is useful for thinner sections, very small parts,
284.-294. RESERVED.
Par 279 Char
Rockwell, superficial bardness Brinell bardness number Rockwell hardness number number, superfielal brale 10-mm. ball, 3000-kg. load penetrator Tenaile Diamond Shore etrengths Hockwell pyramid A-scale, B-scale, D-scale, sclero- (approxi- Rockwell bardness numbers C-scale (Vickers) hardness number ard ball Stand- Kult- gren ball penetra- 60-kz. load, brale 1/16-1n. 100-kg load, diam. penetra- 100-kg. lond, brale 15-kg. 15-N acale, load 30-kg. scale, 30-N load 45-kg. 45-N load scale, hardness number всоре mate) in P. 8. 1. 1000 bardness number® C-scale tor ball tor Col. 1 Col. 2 Col. 3 Col. 4 Col. 5 Col. 6 Col. 7 Col. 8 Col. 9 Col. 10 Col. 11 Col. 12 Col. 13 Col. 14 68 -- 940 85.6 76.9 93.2 84.4 75.4 97 68 67 900 85.0 76.1 92.9 83.6 74.2 95 67 66 865 84.5 75.4 92.5 82.8 73.3 92 66 65 832 739 83.9 74.5 92.2 81.9 72.0 91 65 64 800 722 83.4 73.8 91.8 81.1 71.0 88 64 63 772 705 82.8 73.0 914 80.1 69.9 87 63 62 746 688 82.3 72.2 91.1 79.3 68.8 62 61 720 670 81.8 71.5 90.7 78.4 67.7 83 61 60 697 613 654 T18 70.7 90.2 77.5 66.6 81 60 59 674 599 $£9 1°09 6*69 8°68 76.6 65.5 80 326 59 58 653 587 919 I°08 769 £*68 75.7 64.3 78 315 58 57 633 575 969 9'62 5*89 6*88 S72 63.2 76 305 57 56 613 561 LIS 0°62 L'19 73.9 62.0 75 295 56 55 595 546 099 S81 6°99 87.9 73.0 60.9 74 287 55 54 577 534 543 0°82 1°99 #°48 72.0 59.8 72 278 54 53 560 519 £ZS F°LL 6°98 71.2 58.6 71 269 53 52 544 500 508 ZIS 8°94 9°F9 1°98 70.2 57.4 69 262 52 51 528 487 494 96₺ £94 8°89 698 69.4 56.1 68 253 51 50 513 475 481 IS₺ 6°9L T°£9 68.5 55.0 67 245 50 49 498 464 469 69₺ 1°29 0°S8 67.6 53.8 66 239 49 48 484 451 455 SS₺ LYL £₺8 66.7 52.5 64 232 48 47 471 442 443 £FT I°72 8°09 6°&8 8"99 51.4 68 225 47 46 458 432 432 ZET 9EL 0°09 S£8 8*79 50.3 62 219 46 See footnotes at end of table
FIGURE 7.3.-Rockwell C scale steel hardness numbers comparison table-continued.
Brinell hardness number Rockwell, superficial hardness 10-mm. ball, 8000-kg. load Rockwell bardness numbers number, superficial brale penetrator Tenalle Rockwell bardnede number* C-scale (Vickera) hardness Diamond pyramid number ard ball Stand- Hult- gren ball carbide Tung- sten- ball penetra- A-scale, 60-kg. load, brale B-scale, 1/16-10. 100-kg. load, diam. D-scale, 100-kg. penetra- load, brale 15-kg. scale, 15-N load 80-kg. scale. 30-N load 45-58. scale, 45-N load hardness number Shore scope sciero- strengtha (approxi- mate) in D. e. I. 1000 hardness Rockwell numbers C-scale tor ball tor Col. 1 Col. 2 Col. 3 Col. 4 Col. 5 Col. 6 Col. 1 Col. 8 Col. 9 Col. 10 Col. 11 Col. 12 Col. 13 Col. 14 446 421 421 421 731 59.2 83.0 64.0 49.0 60 212 45 434 409 409 409 725 58.5 82,5 63.1 47.8 58 206 44 423 400 400 400 72.0 57.7 82.0 62.2 46.7 57 201 43 412 390 390 390 71.5 56.9 81.5 61.3 45.5 56 196 42 402 381 381 381 70.9 56.2 80.9 60.4 44.3 55 191 41 392 371 371 371 70.4 55.4 80.4 59.5 43.1 54 186 40 382 362 362 362 69.9 54.6 79.9 58.6 41.9 52 181 39 372 353 353 353 69.4 538 79.4 57.7 40.8 51 176 38 363 344 344 344 68.9 53.1 78.8 56.8 39.6 50 172 37 354 336 336 336 68.4 (109.0) 52.3 78.3 55.9 38.4 49 168 36 345 327 327 327 67.9 (108.5) 51.5 77.7 55.0 37.2 48 168 35 336 319 319 319 67.4 (108.0) 50.8 77.2 54.2 36.1 47 159 34 327 311 311 311 66.8 (920I) 50.0 76.6 53,3 34.9 46 154 33 318 301 301 301 66.3 (107.0) 49.2 76.1 52.1 33.7 44 150 32 310 294 294 294 65.8 (106.0) 48.4 75.6 51.3 32.5 43 146 31 302 286 286 286 65.3 (105.5) 47.7 75.0 50.4 31.3 42 142 30 294 279 279 279 64.7 (104.5) 47.0 74.5 49.5 30.1 41 188 29 286 271 271 271 64.3 (104.0) 46.1 73.9 48.6 28.9 41 184 28 279 264 264 264 63.8 (103.0) 45.2 73.3 47.7 27.8 40 131 272 258 258 258 63.9 (102.5) 44.6 72.8 46.8 26.7 38 197 26 266 253 253 253 62.8 (101.5) 43.8 72.2 45.9 25.5 38 124 25 260 247 247 247 62.4 (101.0) 49.1 71.6 45.0 24.3 37 121 24 254 243 243 243 62,0 100.0 42.1 71.0 44.0 23.1 36 118 23 248 237 237 237 61.5 99.0 41.6 70.5 43.2 22.0 35 115 22 243 231 231 231 61.0 98.5 40.9 69.9 42.3 20.7 35 113 21
PIGUKE TO -доскжен ~ осас і 20_ 238 226 226 226 60.5 97. 8 40. 1 69-4 $1.5 19. 6 110 20 3.13-14
(18) - 230 219 219 219 96. 7 (18)
(16) 222 212 212 212 95. 5
(14) 213 203 203 203 93. 9
(12) 204 194 194 194 92. 3
(10) 196 187 187 187 90. 7 188 179 179 179 89. 5 180 171 171 171 87. 1
(4) 173 165 165 165 85. 5
(2) 166 158 158 158 83. 5
(0) - 160 152 152 152 81. 7 : The values in this table shown in bold-face type correspond to the values shown in the corresponding joint SAE-ABM-ASTH Committee on Hardoess Conversions as printed in ABTH E4S, table 2.
• Values in () are beyond normal range and are given for information only.
* It is possible that steels of various compositions and processing historles will deviate in hardness-tensile strength relationship from the data pres nted in this table. Above the level of Rockwell C43, deviation increases with increasing hardness and the table shall not be used above Bo 48 ercept in the absence of other data specifcally approved by the procuring agency.
Page 136 AC 43.
Section 3. NONDESTRUCTIVE TESTING
295. GENERAL, The field of NDT (nondestructive testing) and inspection is too varied to be covered in detail in this handbook. This section provides a brief description of the various methods that are available for use in aircraft maintenance. The effectiveness of any particular method of NDT inspection depends upon the skill, experience and training of the persona applying the process. Each process is limited in its usefulness as an inspection tool through its adaptability to the particular component to be inspected. Consult the aircraft or product manufacturer for specific instructions regarding NDT inspection of their product.
296. INSPECTION BY MAGNIFYING GLASS AFTER WELDING. Careful examination of all joints with a medium-power magnifying glass (at least 10-power), after first removing all scale, is considered an acceptable method of inspection for repaired structures. The practice of filling steel tubular structures with hot linseed or petroleum base oils, under pressure, in order to coat the inside surface and inhibit corrosion, assists in the detection of weld cracks, as the hot oil will seep through cracks invisible to the eye. This practice, though not justifiable in all cases, is suggested where a very large portion of the structure has been rewelded.
297. MAGNETIC PARTICLE INSPECTION. Magnetic particle inspection of Magnaflux (a patented trade name used by the Magnaflux Corp.) can be used only on magnetic materials;
l.e., iron and steel. Most stainless or high chromium nickel and manganese alloy steels, being nonmagnetic, cannot be inspected by this method. The method consists essentially of detection of discontinuities (cracks, voids, defects, pits, subsurface holes, etc.) by means of accumulation of magnetic particles on the discontinuities when the part has been magnetized. The magnetic particles are applied either dry as a powder or suspended in light oil. F complete magnetic inspection, both circu and longitudinal, magnetization should be e ployed.
CAUTION Improper operation of Magnaflux equipment be cause of faulty equipment or by untrained persons can Jeopardize the airworthinesa of parta bein inspected. Minute electrical arc burns caused durin inspection by improper operation of Magnaflu equipment, can result in eventual fallure of thi
a. Circular magnetization is produced by tral mitting an electric current directly throu the article being tested, or through a centi conductor placed through the part, in whi case defects parallel to the flow of current m be detected. As an example, circular magne zation of a round steel bar would be produc by placing the ends of the steel bar betwe the heads of the magnetic inspection machi and passing a current through the bars. Ma netic particles applied either during or aft passage of the current, or after passage of t current in magnetically retentive steels, wou disclose discontinuities parallel to the axis the bar.
b. Longitudinal magnetization is induced in part by placing the part in a strong magne!
field, such as the center of a coil. Thus, longit dinal magnetization of a round steel bar wou be produced by placing the ends of the bar t tween the heads of a magnetic-inspecti machine and placing the D.C. solenoid arou the bar. After application of the magnet particles, either during or subsequent to ma netization, discontinuities perpendicular to t axis of the bar would be disclosed.
c. Red, black, and sometimes gray particles & used in the wet or dry methods. In the case wet inspection, a fluorescent magnetic partic may also be used. This process is commercial known as Magnaglo. Articles inspected usi Par 295 Chap
atter medium are illuminated by so-called it light, and the magnetic particles glow by pescence causing any defects or indications pe easily visible. The wet inspection procee provides better control and standardiza- 1 of the concentration of magnetic particles, ier application to complex shapes, and indiions that are easier to interpret. This is due the difficulty of obtaining efficient distribu- 1 of the dry powder during magnetization.
e dry procedure is particularly suitable for ecting subsurface defects, such as, when pecting heavy welds, forgings, castings, etc.
e wet continuous process is recommended ' most aircraft work.
1. The presence of accumulations of magnetic ticles in magnetic inspection does not necesily mean that a defect exists. Changes in tion of the part, particularly where the ange in section is very sharp, and also holes illed through a part, will frequently cause fications. Surface defects are most easily deted, however, since a crack will cause a arp line of magnetic particles to appear.
surface defects are less easily detected, ice only a general collection of magnetic rticles will be observed.
e. After magnetic inspection carefully demagtize and clean the parts. Examine for possie evidence of electrical arc burns that may ‚ve occurred during inspection. All metal irticles must be removed and the serviceable irts coated with a suitable preservative.
f. Portable type magnetic particle inspection ruipment such as Sonoflux has been developed ›r use in the detection of surface or slightly ibsurface discontinuities in ferromagnetic rcraft materials and parts. This type equipent usually gives better results when the wet ispension type of indicator, such as that con- ›rming to Specification MIL-1-6868, is used ith the powder supplied by the equipment anufacturer. As in other inspection methods, ›llow the manufacturers' recommendations oncerning use of the procedure.
98. X-RAY OR RADIOGRAPHIC INSPECTION.
-ray may be used on either magnetic or nonagnetic materials for detecting subsurface lap 7 Page 137 voids such as open cracks, blowholes, etc.
When a photographic film or plate is used to record the X-ray (in a similar manner to ex- Posine posing a photographic film), the process is known as radiography. When the X-rays are prosen, t th projected through the part onto a fluorescent she echnig screen, the process is known as fluoroscopy. The technique used for radiography should be capable of indicating the presence of defects having a dimension parallel to the X-ray beam of 3 percent of the thickness of the part being radiographed for magnesium alloys, and 2 percent for all other metals and alloys. Inspection using a fluoroscopic screen is much less sensitive. Consequently, the radiographic method is usually used for inspection and the fluoroscopic method is used for culling.
a. Radiographic inspection is extensively used in the aircraft industry for the inspection of all types of castings including sand castings, permanent-mold castings, die castings, etc. X- ray is particularly useful for this application, since it is capable of disclosing defects which exist below the surface, and also since the open types of defects which may occur in castings (shrinks, blowholes, dross inclusions, etc.) are readily disclosed by proper use of X-rays. In the inspection of forged or wrought metals, on the other hand, X-ray inspection is not used so extensively. This is due to the fact that the process of forging or working may cause defects which originally existed in the metal to become tightwalled cracks. Such defects are somewhat difficult to disclose by X-rays. If doubt exists as to the suitability of the X-ray examination, consult a laboratory familiar with the X-ray examination of aircraft parts.
b. In radiography, values of peak kilovoltage, radiographic density range and penetrometer characteristics are often selected that produce less than optimum radiological data.
This selection of high kilovoltage is made in order to reduce the exposure time. The use of too high a kilovoltage reduces the resolvable detail recorded on the radiographic film. As the kilovoltage is increased, X-rays of shorter wave length and greater penetrating power are produced. This presents a sound argument for increased kilovoltages but does not take into Par 297
account the effects of scatter both within the sample and the radiographic film, which in reality, reduces the resolvability of details recorded on the X-rays.
c. If for some reason a short exposure time is required, a faster film is normally used with a higher kilovoltage; however, this has the effect of increasing the granularity and reducing the resolution on the radiographic material.
d. The use of low voltages results in improved radiographic signal-to-noise ratio and improved resolution. The recommended kilovoltages are shown in figure 7.5.
FIGURE 7.5.-Maximum recommended X-ray kilovolts, Material Atomio No. Man. KV Beryllium 25 Carbon 40 Magnesium 12 50 Alumium 18 75 Titanium 22 120 Steel 22-20 150 Steel 20-28 200 Silver 47 800 Lead 82 1-2 (megavolta)
299. FLUORESCENT PENETRANT. In this method of inspection (Zyglo), the article, which may be of metal, plastic material, etc., is first carefully cleaned to permit the fluorescent material to penetrate cracks and defects. It should be noted that cleaning of aluminum may necessitate stripping of any anodizing, since the anodized film, if formed after the defect, could prevent penetration of the fluorescent material and an anodized film tends to hold penetrants which may obscure defect indications. After the article is cleaned, it is either sprayed, painted, or immersed in a bath of fluorescent penetrant. The penetrant is a light oil which has the property of fluorescing or emitting visible light when excited by invisible radiation in the near ultra-violet range (so-called black light). It is important that the penetrant be given sufficient time to penetrate cracks and defects, and for fatigue cracks a minimum of 80 minutes is stipulated by MIL-I-6866. Heat may also be applied to facilitate entry of the penetrant. After the penetrant has had sufficient time to enter any defects, the excess on Par 298 AC 4:
the surface of the article is washed o water spray. This washing should be ch by inspection with black light, by which r any penetrant left on the surface may I tected. After washing, a developer is us bring out the indication. This developer m in a liquid form or may be a light powde absorbs the penetrant as it oozes from c and defects in the part. The development also be aided by application of heat to the After the indications have been develope‹ part is inspected under black light. Any ices into which the fluorescent material has etrated will show as luminous areas.
Indications which appear are us checked by close inspection with a magni glass, by etching with a suitable acid or ca solution, or it may be necessary to cross-se the part, a procedure which, of course stroys its usefulness. Usually a skilled ope can determine whether an indication act shows a defect or whether it is a false in tion. Also, the internal extent of the defec sometimes be estimated with fair accurat should be noted that this process of inspec like all others, has its limitations. If the orescent material for any reason is not at penetrate into a defect, such a defect cann detected.
300. DYE PENETRANTS. Several dye penet type inspection kits are now available w will reveal the presence of surface crack defects and subsurface flaws which exter the surface of the part being inspected. I penetrant type inspection methods are co:
ered acceptable, provided the part being spected has been thoroughly cleaned, all a are readily accessible for viewing, and manufacturer's recommendations as to me of application are closely followed.
a. Cleaning. An inspection is initiated by cleaning the surface to be inspected of loose scale, oil, and grease. Precleaning usually be accomplished by vapor degrea or with volatile cleaners. Use a volatile cle as it will evaporate from the defects be applying the penetrant dye. Sand blastin not desirable as a cleaning method, since face indications may be obscured. It is not
43.13-1A ary to remove anodic films from parts to be spected, since the dye readily penetrates such ms. Special procedures for removing the exsa dye should he followed.
b. Application of Panefrant. The penetrant is plied by brushing, spraying, or by dipping d allowed to stand for a minimum of 2 mines. Dwell time may be extended up to 15 mines, depending upon the temperature of part d fineness of the defect or when the surface ing inspected is ground. Parts being inected should be dry and heated to at least ° F., but not over 130° F. Very small indicains require increased penetration periods.
t. Removal of Dye Peneirant. Surplus peneint is usually removed by application of a acial cleaner or remover, or by washing with in water and the part allowed to dry. Water he may also be used in conjunction with the over, subject to the manufacturer's recom-
•dations.
Application of Developer. A light and even of developer is applied by spraying, brushor dipping. When dipping, avoid excess aclation. Penetrant which has penetrated cracks or other openings in the surface of naterial will be drawn out by the develresulting in a bright red indication. Some Page 139 idea of the size of the defect may be obtained after experience by watching the size and rate of growth of the indication.
301. ULTRASONIC FLAW DETECTION. Ultrasonic flaw detection equipment has made it possible to locate defects in all types of materials without damaging the material being inspected.
Very small cracks, checks, and voids, too small to be seen by X-ray, are located by means of ultrasonic inspection. An ultrasonic test instrument requires access to only one surface of the material to be inspected, and can be used with either straight line or angle beam testing techniques. The instrument electronically generates ultrasonic vibrations and sends them in a pulsed beam through the part to be tested. Any discontinuity within the part, or the opposite end, will reflect the vibration back to the instrument, which measures the elapsed time between the initial pulse and the return of all reflections and indicates such time lapse on a cathode ray indicator or paper recorder. Ultrasonic inspection requires a skilled operator who is familiar with the equipment being used as well as the inspection method to be used for the many different parts being tested.
302.-312. RESERVED.
Par 300
Page 140 AC 43.13-1A CH Section 4. IDENTIFICATION OF FABRICS AND PLASTICS
313. IDENTIFICATION OF FABRIC. Cotton fabric is often used as covering for wing, fuselage, and control surfaces of aircraft. Acceptable grades of fabric for use on civil aircraft are listed in Chapter 3. In general, the fabric can be readily identified by a continuous marking to show the manufacturer's name or trademark and specification number. This marking may be found stamped along the selvage edge. The specification number for grade "A" fabric is AMS-3806, and for the intermediate grade AMS-3804. The corresponding FAA Technical Standard Order * Numbers for these materials are TSO-C15 and 150-C14, respectively. Increasing interest in* the use of linen and certain synthetic fabrics in lieu of cotton has been noted. Identity of such materials should always be verified by the user.
314. IDENTIFICATION OF PLASTICS. Plastics cover a broad field of organic synthetic resins and may be divided into two main classifications thermoplastic and thermosetting plastics.
a. Thermoplostics. Thermoplastics softened by heat and can be dissolved in varic organic solvents. Two kinds of transpare thermoplastic materials are commonly employ in windows, canopies, etc. These materials s known as acrylic plastics and cellulose acets plastics. These two plastics may be distinguish by the absence of color, the greater transparen and the greater stiffness of the acrylic as co pared to the slight yellow tint, lower transp ency, and greater flexibility of cellulose aceta
b. Thermosetting Plastics. Thermosetting pl tics do not soften appreciably under hent may char and blister at temperatures of 204 260° C. (400° to 500° F.). Most of the mo products of synthetic resin composition, suc phenolic, urea-formaldehyde, and melan formaldehyde resins, belong to the thermoset group.
315.-320. RESERVED.
Par 313
C 43.13-1A CHG 1 Page 140~1 75 Section 5. CABIN INTERIOR MATERIALS, FIRE PROTECTION QUALITIES
21. REQUIREMENTS FOR FIRE PROTECTION. The leaning, repairing: and/or replacement of cabin nterior materials necessitates continuing complince with the fire protection requirements of the ARs. A recent field survey on this matter reor maintaining cabin interior materials with ealed a wide variance in the procedures used spect to the fire protection qualities of these aterials.
a. Inferior Materials. The methods, techniques, actices, and materials used in the cleaning, reir, and replacement of cabin materials must et the requirements of Section 43.13 of the
• Fire Protection. The requirements relative ire protection qualities of cabin interior maas are specified in:
(1) Section 121.312, for aircraft operated under Parts 121, 123, and 135.
(2) Section 127.91, for helicopters used in passenger service under Part 127.
c. Source of Information. If information regarding the original or properly altered fire protection qualities of certain cabin interior materials is not available, requests for this information should be made to the aircraft manufacturers or the local FAA regional office, specifying the model aircraft, the aircraft manufacturer, the date the aircraft was manufactured or the serial number, and the FAR Part under which the aircraft is operated (i.e., Part 91, Part 121, etc.).
322.-325. RESERVED.
Par 321
AC 43.13-1А Page 141 1972 Chapter 8. AIRCRAFT EQUIPMENT Section 1. LANDING GEAR EQUIPMENT
326. GENERAL. Many factors affect the scope and frequency of landing gear aystem inspection and maintenance. The possibility of system malfunction increases with severe operating conditions, such as pilot training and agricultural operations. Cracks are the foremost area of concern, followed closely by worn, sheared, bent, or broken bolts, and elongated boltholes, Although these defects occur during normal aircraft usage, adverse operating conditions accelerate the problem.
Improper adjustment or lubrication can also cause malfunctioning, especially in landing gear retraction mechanisms. Excessive lubrication or the wrong type of lubricant can often be as bad or worse than none at all. With regard to lubrication, closely follow the manufacturer's service and maintenance instructions.
residue around bolts, rivets, and pins is a good indication of looseness or wear, Thoroughly clean and re-inspect the landing gear to determine the extent of any damage or wear. Some components may require removal and complete disassembly for detailed inspection. Others may require a specific check using an inspection process such as dye penetrant, magnetic particle, radiographic, ultrasonic, or eddy current (see Chapter 7). The frequency, degree of thoroughness, and selection of inspection methods are dependent upon the age, use, and general condition of the aircraft.
Inspect the aircraft structure surrounding any visible damage to insure that no secondary damage remains undetected. Forces can be transmitted along the affected member to remote areas where subsequent normal loads can cause failure at a later date.
CAUTION Inspect grease fittings after applying high pressure lubricant to determine that the spring-loaded ball has reseated, Failure of the ball to reseat is an indication of an internal fallure of the fitting which can result in serious damage to the part
327. INSPECTION. Inspect the aircraft landing gear and all associated hardware closely for cracks, cleanliness, lubrication, leaks, deformation, excessive wear, and security of attachments. Before removing any accumulated dirt, cloaely observe the area being inspected while the wingtips are gently rocked up and down.
Excessive motion between normally close fitting components may indicate wear, cracks, or improper adjustment. If a crack exists, it will generally be indicated by dirt or metallic part!- cles which tend to outline the fault. Seepage of rust inhibiting ofa, used to coat internal surfaces of steel tuber, also assists in the early detection of cracks. in addition, a sooty, olly
a. Types of Malfunctions.
(1) Cracks. Príme locations for cracks on any landing gear are bolts, boltholes, pins, rivets, and welds. The following are typical locations where cracks may develop:
(a) Bolts. Most suaceptible areas are at the radius between the head and the shank, and in the location where the threads join the shank, as shown in figure 8.1.
(b) Boltholes and Pinholes, Cracks primarily occur at the edge of boltholes or pinholes on FIOURE 8.1.Typical bolt cracks.
Chap 8 Par 326