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
the surface and down inside the bore. (See figures 8.2 and 8.3.)
(c) Riveted Joints or Seams, The usual types of failure in this area are deformation of the rivet heads and skin cracks originating at the rivet holes.
(d) Rod Ends. Cracks and subsequent failures usually begin at the thread end near the bearing and adjacent to or under the jam nut.
(See figure 8.1.)
TYPICAL LANDING GEAR FITTING - CRACKS FIGURE 8.2.-Typical cracks near boltholes.
FIGURE 8.8.- Typical bolthole cracks.
FIGURE 8.4.- Typical rod-end cracks.
Par 327 AC 43.13-1A 1972
(e) Welds. Cracks develop primarily along the edge of the weld adjacent to the base metal and along the centerline of the bead.
(2) Elongated holes are especially prevalent in taper-pin holes and boltholes or at the riveted joints of torque tubes and push-pull rods.
(See figure 8.5.)
FIGURE 8.5.-Typical torque tube bolthole elongation.
(3) Deformation is common in rods and tubes and usually is noticable as stretched, bulged, or bent sections. As deformations of this type are difficult to see, the hands should be passed along the tube to feel for evidence of this discrepancy. Deformation of sheet metal web sections, at landing-gear component attachment points, usually can be seen when the area is highlighted with oblique lighting.
b. Landing Gear Components. The following items are usceptible to service difficulties and should be given attention.
(1) Shock Absorbers. Inspect the entire shock-strut for evidence of leaks, cracks, and possible bottoming of the piston, as this condition causes overloading of landing gear components and contributes to fatigue cracks. Check all bolts, boltholes, pins, and bushings for condition, lubrication and proper torque values.
Grease fitting holes (pressure type) are especially vulnerable to cracks and cross-threading damage. Check all safety wire and other locking devices, especially at the main packing gland nuts.
When assembling shock-struts, use the correct type and number of "O"-rings, chevron seals, and backup rings. Use only the correct filler valve core assembly, and follow the manufacturer's instructions when servicing with fluid and air. Either too much or too little air or oil will affect aircraft handling characteristics during taxi, takeoff, and landing, and can cause structural overloads.
Shock cords and rubber discs deteriorate with age and exposure. When this type of shock absorber is used, inspect for general con- Chap 8
AC 43.13-1A 1972 dition, i.e., cleanliness, stretching, fraying, and broken strands. These components must be kept free of petroleum products as they accelerate deterioration of the rubber.
(2) Nose Gear Assembly. Attention should be given to the steering mechanism and should include items such as: torque-links (scissors), torque-tubes, control rods and rod-end bearings, shimmy dampers, cables, and turning stops. In addition, check all nose landing gear components, including mud scrapers and slush deflectors, for damage from natural elements.
(a) Towing of some aircraft with the rudder locks installed may cause damage to the nose steering linkage and rudder control sygtem. Exceeding the steering or towing stops should be followed by a close inspection of the entire nose steering assembly. A broken steering stop will allow turning beyond the design limit, transmitting excessive loads to structures and to the rudder control system. It is recommended that the nose steering arc limits be indicated on the steering collar or fuselage.
(b) Inspect ahimmy dampers for leakage around the piston ahaft and at fluid line connections, and for abnormal wear or looseness around the pivot points. Also check for proper rigging, "bottoming" of the piston in the cylinder, and the condition of the external stops on the steering collar.
(3) Tailwheels. Disassembly, cleaning, and rerigging of tailwheels are periodically necessary. Inspect for loose or broken bolts, broken springs, lack of lubrication, and general condition. Check steerable tailwheels for proper steering action, steering-horn wear, clearances, and for security and condition of steering springs and cables.
(4) Gear Doors. Inspect gear doors frequently for cracks, deformation, proper rigging, and general condition. Gear door hinges are especially susceptible to progressive cracking, which can ultimately result in complete failure, allowing the door to move and cause possible jamming of the gear. This condition could also result in the loss of the door in flight. In addition, check for proper safetying of the hinge pins and for distorted, sheared, loose, or cracked hinge rivets. Inspect the Chap 8 Page 143 wheelwells for improper location or routing of components and related tubing or wiring which could interfere with the travel of the gear door actuating mechanisms.
(5) Floats. In order to maintain floats in an airworthy condition, frequent inspections should be made because of the rapidity with which corrosion takes place on aluminum alloy metal parts, particularly when the aircraft is operated in salt water. Examine metal floats and all metal parts on wooden or fiberglas floats for corrosion and take corrective action in accordance with the procedures described in Chapter 6. Repair damage to metal floats in the general manner outlined in Chapter 2 pertaining to aluminum and aluminum alloy structures. In the case of wooden floats, make repairs in accordance with general procedure outlined in Chapter 1. Repair fiberglass floats in accordance with the manufacturer's instructions or other acceptable practices.
(6) Skis and Ski Installation. It is advisable to examine aki installations frequently to keep them maintained in airworthy condition. If shock cord is used to keep the ski runner in proper trim, periodically examine to assure that the cord has enough elasticity to keep the runner in its required attitude and the cord is not becoming loose or badly frayed. Replace old or weak shock cords. When other means of restraint are provided, examine for excessive wear and binding, and replace or repair when of cable attachment, both on the ski and the air- such conditions are found. Examine the points SESTE plane structure, for bent lugs due to excessive loads having been imposed while taxiing over rugged terrain or by trying to break loose frozen skis. If skis which permit attachment to the wheels and tires are used, maintain proper tire pressure as underinfiated tires may push off the wheels if appreciable side loads are developed in landing or taxiing.
(a) Repair of Ski Runners. Fractured wooden ski runners usually require replacement. If a split at the rear end of the runner does not exceed 10 percent of the ski length, it may be repaired by attaching one or more wooden crosspieces across the top of the runner using glue and bolts. Bent or torn metal Par 327
runners may be straightened if minor bending has taken place and minor tears may be repaired in accordance with procedures recommended in Chapter 2 relative to repair of metal structures.
(b) Ski Pedestals.
1. Tubular pedestals. Damaged pedestals made of steel tubing may be repaired by using standard tube splices as shown in Chapter 2, figures 2.5 and 2.15.
2. Cast pedestals. Consult an FAA representative on the repair of cast pedestals.
3. Sheet metal pedestals. Repair damaged pedestals made of aluminum alloy sheet in the general manner outlined in Chapter 2.
(7) Wheels. Inspect wheels at periodic intervals for cracks, corrosion, dents, distortion, and faulty bearings in accordance with the manufacturer's service information. In splittype wheels, recondition boltholes which have become elongated due to some play in the through-bolt, by the use of inserts or other suitable means. Pay particular attention to the condition of the through-bolts and nuts. Carefully inspect wheels used with tubeless tires for damage to the wheel flange and for proper sealing of the valve. The sealing ring used between the wheel halves should be free of damage and deformation. In bolting wheel halves together, tighten the nuts to the proper torque value.
Periodically accomplish an inspection to assure the nuts are tight and there is no movement between the two halves of the wheel. Any movement between the wheel halves normally causes elongation of the boltholes. If the wear is too great to be corrected, as stated above, it may necessitate scrapping of the wheel. Maintain grease retaining felts in the wheel assembly in a soft, absorbent condition. If any have become hardened, wash them with a petroleum-base cleaning agent; if this fails to soften them, they should be replaced.
(a) Corrosion of Wheels. Thoroughly clean wheels if corroded and then examine for soundness. Smooth and repaint bare corroded spots with a protective coating such as zinc chromate primer and aluminum lacquer, or some other equally effective coating to prevent further corrosion. Replace wheels having se- Par 327 AC 43.13-1A 1972 vere corrosion which might affect their strength.
(b) Dented or Distorted Wheels. Replace wheels which wobble excessively due to deformation resulting from a severe side-load impact.
In questionable cases, consult the local representative of the FAA concerning the airworthiness of the wheels. Dents of a minor nature do not affect the serviceability of a wheel.
(c) Wheel Bearings. Periodically inspect wheel bearings for condition. Replace damaged or excessively worn parts. Pack bearings with a high-melting-point grease prior to their installation. Avoid preloading the wheel bearing when installing on aircraft by tightening the axle nut just enough to prevent wheel drag or sideplay.
(8) Brakes. Maintain the clearance between the moving and stationary parts of a brake in accordance with the manufacturer's instructions. Disassemble and inspect the brake periodically and examine the parts for wear, cracks, warpage, corrosion, elongated holes, etc. If any of these or other faults are indicated, repair, recondition, or replace the affected parts in accordance with the manufacturer's recommendations. Surface cracks on the friction surfaces of the brake drums occur frequently due to high surface temperatures These surface cracks may be disregarded as seriously affecting the airworthiness until they become cracks of approximately 1 inch in length.
(a) Hydraulic Brakes. For proper maintenance, periodically inspect the entire hydraulic system from the reservoir to the brakes, Maintain the fluid at the recommended level with proper brake fluid. When air is present in the brake system, bleed in accordance with the manufacturer's instructions. Replace flexible hydraulic hose which has deteriorated due to long periods of service and replace hydraulic piston seals when there is evidence of leakage.
Service antiskid units according to the manufacturer's instructions.
(b) Mechanical Brakes. Keep the working parts of mechanically operated brakes free from dirt and foreign matter so the brakes can work freely at all times. Slack in the linkage system must be kept to a minimum.
Chap 8
AC 43.13-1A 1972
(9) Micro-Switches. Inspect micro-switches for security of attachment, cleanliness, general condition, and proper operation. Check associated wiring for chafing, proper routing, and to determine that protective covers are installed on wiring terminals, if required. Check the condition of the rubber dust boots which protect the micro-switch plungers from dirt and corrosion.
328. CLEANING AND LUBRICATING. It is recommended that only easily removable neutral solutions be used when cleaning landing gear components. Any advantage, such as speed or effectiveness, gained by using cleaners containing corrosive materials, can be quickly counteracted if these materials become trapped in close-fitting surfaces and crevices. Wear points, such as landing gear up-and-down latches, jack-screws, door hinges, pulleys, cables, bellcranks, and all pressure-type grease fittings should be relubricated after every cleaning operation. To obtain proper lubrication of the main support bushings, it may be necessary to jack the aircraft.
NoTE: Anytime the aircraft is on jacks, check the landing gear main support bushings for wear. Consult the aircraft manufacturer's overhaul manual for specific wear tolerances.
During winter operation, excess grease may congeal and cause increased loads on gear retraction system electric motors and hydraulic pumps. This condition can lead to component malfunctions; therefore, it is recommended lubrication.
329. EMERGENCY SYSTEMS. Exercise emergency landing gear systems periodically to insure proper operation and to prevent inactivity, dirt, and corrosion from rendering the system inoperative when needed. Most emergency systema employ either mechanical, pressure-bottle or free-fall extension capabilities. Check for proper safetying of triggering mechanisms, and for the presence of required placards and Chap & Page 145 necessary accessories such as cranks, levers, handles, etc.
330. SPECIAL INSPECTIONS. Any time an aircraft has experienced a hard or overweight landing, it is recommended that a special structural inspection, which includes the landing gear, be performed. Typical areas which require special attention are landing gear support trusses for cracked welds, sheared bolts and rivets, and buckled structures; wheels and tires for cracks and cuts; and upper and lower wing surfaces for wrinkles, deformation, and loose or sheared rivets. If any damage is found, a detailed inspection is recommended.
331. RETRACTION TESTS. Periodically, perform a complete operational check of the landing gear retraction system. Inspect the normal extension and retraction system, the emergency extension system, and the indicating and emergency warning system. Determine that the actuating cylinders, linkage, slide tubes, sprocketa, chain or drive gears, gear doors, and the up-and-down locks are in good condition and properly adjusted and lubricated. In addition an electrical continuity check of micro-switches and associated wiring is recommended. Only qualified personnel should attempt adjustments to the gear position and warning system microswitches and then only by closely following the manufacturer's recommendations.
332. TIRES. It is essential that tires be inspected frequently for cuts, worn spots, buiges on the sidewalls, foreign bodies in the treads, and tread condition. Defective tires may be repaired or retreaded in accordance with the following paragraphs. The term, "retread," for the purpose of this advisory circular, refers to the several means of restoring a used tire, whether by applying a new tread alone or tread and sidewall material in varying amounts. It refers as well to the process of extending new sidewall material to cover the bead area of the tire. Aircraft tires are identified by type and rating (figure 8.6).
Par 327
rage 146 AC 43.13-1A 1972 MF G under (b) Bead injuries that exceed the limits Type FAR 87.167 Design and rating outlined in paragraph (1) (a) or affect the seal (TSO C62) of the bead on tubeless-type tires.
No_. Smooth contour.! (c) Evidence of separation between plies No. - High pressure.! or around bead wire.
Yes_ Low pressure.? (d) Injuries requiring reinforcement.
V_ VI_ IV No. No_ No_. N/A. Low profile! Extra low presaure.! lined under paragraph (1) (b) and all injuries This includes injuries larger than those out- VII. Yes_. Extra high pressure "low speed".? requiring sectional repair.
VII Yes_ Extra high pressure "high (e) Kinked or broken beads.
speed." • (f) Weathering or radial cracks extendvI. VIII. Yes_ Yes_ Extra high pressure Extra bigh pressure-low pro- file "low speed." › -Low pro- ing into the cord body. (g) Evidence of blisters or heat damage.
file high speed." (h) Cracked, deteriorated, or damaged inner liners of tubeless tires.
I Inactive for new dealgn.
• Low speed for ground speeds below 160 m.p.h
• High speed for ground speeds above 160 m.p.b.
FIGURE 8.6.-Aircraft tire types and ratings.
Tires rated for groundspeeds in excess of 160
m.p.h. have the type and rating embossed on the sidewall.
a. Repair and Retreading of Low-Speed Tires.
The following procedures are applicable to other than Type VII and Type VIII high-speed aircraft tires.
(1) Tires having injuries of the following types may be repaired:
(a) Bead injuries where only the chafe resistant material is damaged or loose, or where minor injuries do not penetrate into more than 25 percent of the tire plies, up to a maximum of three damaged plies.
(b) Injuries in tread or sidewalls may be repaired by the spot repair method. This includes cuts in the tread area that are smaller than 1/2 inch in length and do not penetrate more than the following number of plies into the cord body.
Ply rating: out depth Макітит Less than 8 None.
8 through 16 2 plies.
More than 16 - - 4 plies.
(2) Nonrepairable Tires. If any of the following conditions exist, repair of the tire is not recommended:
(a) Evidence of flex breaks.
(3) Spot Repairs. Use repair methoda conforming to the best aviation industry practices.
Skive injuries require spot repairs at an approximate 45° angle to remove damaged rubber and cords.
Buff away exposed cord (refer to paragraph
(1) (b) for cord damage limits) leaving only the ends at the skive line and the rubber between the cord plies exposed. Clean the area thoroughly before applying the vulcanizing cement. As soon as the cement is completely dry, cover the skived area of the carcass with repair cushion gum. Fill the cavity in the carcass with repair cushion gum and roll to remove air. The tread cavity can then be filled with tread repair gum well-rolled, to provide a solid repair.
(4) Bead or Chafe Repairs. Use repair methods conforming to the best aviation industry practices. Trim the frayed fabric ends. Turn back the loose area, buff and clean the surface, and immediately cement. Secure the fabric back in position. Vulcanize repairs larger than 2 inches.
(5) Retreadable Tires. Tires which are sound or which can be repaired as listed above may be retreaded as set forth in Specification MIL-R-7726.
(6) Marking of Retreaded Tires, Permanently mark each retreaded tire. Whenever it is necessary to replace the area containing the original marking, such markings must be replaced. In addition, each retreaded tire will:
(a) Display the letter "R" followed by a Par 332 Chap 8