Par 4-93 Page 4-180
A- Streamline Tube Length of Minor Axis, Plate Widths.
B- Distance of First Plate From Leading Edge, ²/³ A.
C- Streamline Tube Length of Major Axis.
S.L. Size A B C 6A 1” .572 .82 1.340 3.430 1-¼ .714 .476 1.670 4.280 1-½ .858 .572 2.005 5.150 1-¾ 1.000 .667 2.339 6.000 2 1.144 .762 2.670 6.860 2-¼ 1.286 .858 3.008 7.720 2-½ 1.430 .954 3.342 8.580
FIGURE 4-45. Streamline tube splice using plates (applicable to landing gear).
Par 4-93 Page 4-181
(A), (B), AND (C) ARE TYPES OF REPAIRABLE AXLE ASSEMBLIES. ASSEMBLIES ORIGINALLY HEAT TREATED MUST BE REHEAT TREATED AFTER WELDING.
F IGURE 4-46. Representative types of repairable axle assemblies.
Par 4-93 Page 4-182 (and 4-80)
Par 4-104 Page 4-183 FIGURE 4-47. Landing gear assemblies that CANNOT be repaired by welding.
4-94.4-103. [RESERVED.]
Par 4-104 Page 4-184 SECTION 6. WELDING AND BRAZING SAFETY
GENERAL. A number of inherent hazards exist in the use of oxy-fuel welding and cutting apparatus. It is necessary that proper safety and operating procedures are understood. A thorough understanding of the proper safety and operating procedures minimizes the hazards involved and adds to the pleasure and efficiency of your work.
FIRE AND EXPLOSION SAFETY. Fires occur in welding areas because flammables are left where they can be ignited by welding sparks or gas welding flames. Before welding, clear the welding area of all flammables such as rags, paper, wood, paint cans, solvent, and trash containers. Do not weld in areas where flammables are present.
Never weld any tank or radiator that has had a flammable in it, including gasoline, av-gas, motor oil, hydraulic fluid, or any other liquid that could ignite if the vapor and temperature should reach a flashpoint.
Explosions often occur when empty tanks are being welded or cut open with a torch.
If welding such tanks or radiator coolers is absolutely necessary, the tank must first be washed with a causticbased, water-soluble liquid, rinsed with plenty of clear water, and then dried. Then, before welding, the tank or container should be thoroughly purged with argon, or other inert gas, while the welding is in process.
WELDING WORK AREA.
The work area must have a fireproof floor, concrete floors are recommend.
Use heat-resistant shields to protect nearby walls or unprotected flooring from sparks and hot metal.
Maintain an adequate suction ventilation system to prevent the concentration of oxygen/fuel gas, flammable gases, and/or toxic fumes. It is important to remember that oxygen will not burn. The presence of oxygen, however, serves to accelerate combustion, and causes materials to burn with great intensity.
CAUTION: Oil and grease in the presence of oxygen can ignite and burn violently.
A completely clean welding shop area with white walls, ceiling, and floor; and with plenty of light, is better for welding. The better the lighting conditions, the easier it is to see the weld puddle and make excellent aircraft-quality welds.
During oxy-fuel processes use work benches or tables with fireproof tops. Fire bricks commonly top these surfaces and support the work.
Chain or otherwise secure oxygen and fuel gas cylinders to a wall, bench, post, cylinder cart, etc. This will protect them from falling and hold them upright.
FIRE PROTECTION. Practice fire prevention techniques whenever oxy-fuel operations are in progress. Simple precautions prevent most fires, and minimize damage in the event a fire does occur. Always practice the following rules and safety procedures.
Par 5-1 Page 5-185 Inspect oxy-fuel apparatus for oil, grease, or damaged parts. DO NOT use the oxy-fuel apparatus if oil or grease is present or if damage is evident. Have the oxy-fuel appara tus cleaned and/or repaired by a qualified repair technician before it is used.
Never use oil or grease on or around any oxy-fuel apparatus. Even a trace of oil or grease can ignite and burn violently in the presence of oxygen.
Keep flames, heat, and sparks away from cylinders and boxes.
Flying sparks can travel as much as 35 feet. Move combustib les a safe distance away from areas where oxy-fuel operations are performed.
Use approved heat-resistant shields to protect nearby walls, floor, and ceiling.
Have a fire extinguisher of the proper class (ABC) and size in the work area. Inspect it regularly to ensure that it is in proper working order. Know how it is used.
Use oxy-fuel equipment only with the gases for which it is intended.
DO NOT open an acetylene cylinder valve more than approximately 1-1/2 turns and pr eferably no more than 3/4 of a turn. Keep the cylinder wrench, if one is required, on the cylinder valve so the cylinder may be turned off quickly, if necessary.
On all gases except acetylene, open the cylinder valve completely to seal the cylinder back-seal packing.
Never test for gas leaks with a flame. Use an approved leak-detector solution.
When work is complete, inspect the area for possible fires or smoldering materials.
Special care should be taken when welding structural tubing that has been coated on the inside with linseed oil.
Smoke and fire may be generated by the heat of the torch. Ensure that an observer with a fire extinguisher is close.
PROTECTIVE APPAREL.
Protect yourself from sparks, flying slag, and flame brilliance at all times.
For gas welding and brazing, use number 3 or 4 green-shaded tempered lenses.
When gas welding aluminum, use cobalt-blue tint lenses.
When arc welding, including TIG, MIG, and plasma cutting; use number 9 to 12 green lenses and a full face-and-neck covering helmet.
Electronically darkening lenses provide number 3 to 12 automatic darkening as soon as the arc is ignited.
Wear protective gloves, sleeves, aprons, and lace-up shoes to protect skin and clothing from sparks and slag.
CAUTION: Keep all clothing and protective apparel absolutely free of oil or grease.
FIRST-AID KITS. Always keep a special welder’s first-aid kit where it is easily accessible. Burns are the most common welding accidents.
Par 5-1 Page 5-186
4-110.4-128. [RESERVED.]
Par 5-1 Page 5-187 CHAPTER 5. NONDESTRUCTIVE INSPECTION (NDI)
SECTION 1. GENERAL
GENERAL. The field of NDI is too varied to be covered in detail in this Advisory Circular (AC).
This chapter provides a brief description of the various Nondestructive Testing (NDT) used for inspection of aircraft, powerplant, and components in aircraft inspection. The effectiveness of any particular method of NDI depends upon the skill, experience, and training of the person(s) performing the inspection process. Each process is limited in its usefulness by its adaptability to the particular component to be inspected. Consult the aircraft or product manufacturer’s manuals for specific instructions regarding NDI of their products. (Reference AC 43-3, Nondestructive Testing in Aircraft, for additional information on NDI.
The product manufacturer or the Federal Aviation Administration (FAA) generally specifies the particular NDI method and procedure to be used in inspection.
These NDI requirements will be specified in the manufacturer’s inspection, maintenance, or overhaul manual; FAA Airworthiness Directives (AD);
Supplemental Structural Inspection Documents (SSID);
or manufacturer’s service bulletins (SB). However, in some conditions an alternate NDI method and procedure can be used. This includes procedures and data developed by FAA certificated repair stations under Title 14 of the Code of Federal Regulations, (14 CFR), part 145.
APPROVED PROCEDURES.
Title 14 CFR, part 43 requires that all maintenance be performed using methods, techniques, and practices prescribed in the current manufacturer’s maintenance manual or instructions for continued airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the administrator. If the maintenance instructions include materials, parts, tools, equipment, or test apparatus necessary to comply with industry practices then those items are required to be available and used as per part 43.
NDT LEVELS. Reference Air Transport Association (ATA) Specification 105-Guidelines For Training and Qualifying Personnel In Nondestructive Testing Methods.
Level I Special.
Initial classroom hours and on-the-job training shall be sufficient to qualify an individual for certification for a specific task. The individual must be able to pass a vision and color perception examination, a general exam dealing with standards and NDT procedures, and a practical exam conducted by a qualified Level II or Level III certificated person.
Level I/Level II.
The individual shall have an FAA Airframe and Powerplant Mechanic Certificate, complete the required number of formal classroom hours, and complete an examination.
Level III.
The individual must have graduated from a 4 year college or university with a degree in engineering or science, plus 1 year of minimum experience in NDT in an assignment comparable to that of a Level II in the applicable NDT methods: or
The individual must have 2 years of engineering or science study at a university,
Par 5-1 Page 5-188 college, or technical school, plus 2 years of experience as a Level II in the applicable NDT methods: or
The individual must have 4 years of experience working as a Level II in the applicable NDT methods and complete an examination.
TRAINING, QUALIFICATION, AND CERTIFICATION. The success of any NDI method and procedure depends upon the knowledge, skill, and experience of the NDI personnel involved. The person(s) responsible for detecting and interpreting indications, such as eddy current, X-ray, or ultrasonic NDI, must be qualified and certified to specific FAA, or other acceptable government or industry standards, such as MIL-STD-410, Nondestructive Testing Personnel Qualification and Certification, or Air Transport Association (ATA) Specification 105-Guidelines for Training and Qualifying Personnel in Nondestructive Testing Methods. The person should be familiar with the test method, know the potential types of discontinuities peculiar to the material, and be familiar with their effect on the structural integrity of the part.
FLAWS. Although a specific discussion of flaws and processes will not be given in this AC, the importance of this area should not be minimized. Inspection personnel should know where flaws occur or can be expected to exist and what effect they can have in each of the NDI test methods. Misinterpretation and/or improper evaluation of flaws or improper performance of NDI can result in serviceable parts being rejected and defective parts being accepted.
All NDI personnel should be familiar with the detection of flaws such as: corrosion, inherent flaws, primary processing flaws, secondary processing or finishing flaws, and in-service flaws. The following paragraphs classify and discuss the types of flaws or anomalies that may be detected by NDI.
Corrosion. This is the electrochemical deterioration of a metal resulting from chemical reaction with the surrounding environment. Corrosion is very common and can be an extremely critical defect. Therefore, NDI personnel may devote a significant amount of their inspection time to corrosion detection.
Inherent Flaws. This group of flaws is present in metal as the result of its initial solidification from the molten state, before any of the operations to forge or roll it into useful sizes and shapes have begun. The following are brief descriptions of some inherent flaws.
Primary pipe is a shrinkage cavity that forms at the top of an ingot during metal solidification, which can extend deep into the ingot. Failure to cut away all of the ingot shrinkage cavity can result in unsound metal, called pipe, that shows up as irregular voids in finished products.
Blowholes are secondary pipe holes in metal that can occur when gas bubbles are trapped as the molten metal in an ingot mold solidifies.
Many of these blowholes are clean on the interior and are welded shut into sound metal during the first rolling or forging of the ingot.
However, some do not weld and can appear as seams or laminations in finished products.
Segregation is a nonuniform distribution of various chemical constituents that can occur in a metal when an ingot or casting solidifies.
Segregation can occur anywhere in the metal and is normally irregular in shape. However, there is a tendency for some constituents in the metal to concentrate in the liquid that solidifies last.
Par 5-5 Page 5-189 Porosity is holes in a material’s surface or scattered throughout the material, caused by gases being liberated and trapped as the material solidifies.
Inclusions are impurities, such as slag, oxides, sulfides, etc., that occur in ingots and castings. Inclusions are commonly caused by incomplete refining of the metal ore or the incomplete mixing of deoxidizing materials added to the molten metal in the furnace.
Shrinkage cracks can occur in castings due to stresses caused by the metal contracting as it cools and solidifies.
Primary Processing Flaws. Flaws which occur while working the metal down by hot or cold deformation into useful shapes such as bars, rods, wires, and forged shapes are primary processing flaws. Casting and welding are also considered primary processes although they involve molten metal, since they result in a semi-finished product. The following are brief descriptions of some primary processing flaws:
Seams are surface flaws, generally long, straight, and parallel to the longitudinal axis of the material, which can originate from ingot blowholes and cracks, or be introduced by drawing or rolling processes.
Laminations are formed in rolled plate, sheet, or strip when blowholes or internal fissures are not welded tight during the rolling process and are enlarged and flattened into areas of horizontal discontinuities.
Cupping is a series of internal metal ruptures created when the interior metal does not flow as rapidly as the surface metal during drawing or extruding processes. Segregation in the center of a bar usually contributes to the occurrence.
Cooling cracks can occur in casting due to stresses resulting from cooling, and are often associated with changes in cross sections of the part. Cooling cracks can also occur when alloy and tool steel bars are rolled and subsequently cooled. Also, stresses can occur from uneven cooling which can be severe enough to crack the bars. Such cracks are generally longitudinal, but not necessarily straight. They can be quite long, and usually vary in depth along their length.
Flakes are internal ruptures that can occur in metal as a result of cooling too rapidly.
Flaking generally occurs deep in a heavy section of metal. Certain alloys are more susceptible to flaking than others.
Forging laps are the result of metal being folded over and forced into the surface, but not welded to form a single piece. They can be caused by faulty dies, oversized dies, oversized blanks, or improper handling of the metal in the die. They can occur on any area of the forging.
Forging bursts are internal or external ruptures that occur when forging operations are started before the material to be forged reaches the proper temperature throughout.
Hotter sections of the forging blank tend to flow around the colder sections causing internal bursts or cracks on the surface. Too rapid or too severe a reduction in a section can also cause forging bursts or cracks.
A hot tear is a pulling apart of the metal that can occur in castings when the metal contracts as it solidifies.
A cold shut is a failure of metal to fuse. It can occur in castings when part of the metal being poured into the mold cools and does not fuse with the rest of the metal into a solid piece.
Par 5-5 Page 5-190 Incomplete weld penetration is a failure of the weld metal to penetrate completely through a joint before solidifying.
Incomplete weld fusion occurs in welds where the temperature has not been high enough to melt the parent metal adjacent to the weld.
Weld undercutting is a decrease in the thickness of the parent material at the toe of the weld caused by welding at too high a temperature.
Cracks in the weld metal can be caused by the contraction of a thin section of the metal cooling faster than a heavier section or by incorrect heat or type of filler rod. They are one of the more common types of flaws found in welds.
Weld crater cracks are star shaped cracks that can occur at the end of a weld run.
Cracks in the weld heat-affected zone can occur because of stress induced in the material adjacent to the weld by its expansion and contraction from thermal changes.
A slag inclusion is a nonmetallic solid material that becomes trapped in the weld metal or between the weld metal and the base metal.
Scale is an oxide formed on metal by the chemical action of the surface metal with oxygen from the air.
Secondary Processing or Finishing Flaws. T h i s category includes those flaw s associated with the various finishing operations, after the part has been rough-formed by rolling, forg ing, casting or welding.
Flaws may be introduced by heat treating, grinding, and similar processes. The following are brief descriptions of some secondary processing or finishing flaws.
Machining tears can occur when working a part with a dull cutting tool or by cutting to a depth that is too great for the material being worked. The metal does not break away clean, and the tool leaves a rough, torn surface which contains numerous short discontinuities that can be classified as cracks.
Heat treating cracks are caused by stresses setup by unequal heating or cooling of portions of a part during heat treating operations. Generally, they occur where a part has a sudden change of section that could cause an uneven cooling rate, or at fillets and notches that act as stress concentration points.
Grinding cracks are thermal type cracks similar to heat treating cracks and can occur when hardened surfaces are ground. The overheating created by the grinding can be caused by the wheel becoming glazed so that it rubs instead of cutting the surface; by using too little coolant; by making too heavy a cut; or by feeding the material too rapidly. Generally, the cracks are at right angles to the direction of grinding and in severe cases a complete network of cracks can appear. Grinding cracks are usually shallow and very sharp at their roots, which makes them potential sources of fatigue failure.
Etching cracks can occur when hardened surfaces containing internal residual stresses are etched in acid.
Plating cracks can occur when hardened surfaces are electroplated. Generally, they are found in areas where high residual stresses remain from some previous operation involving the part.
Par 5-5 Page 5-191 In-Service Flaws. These flaws are formed after all fabrication has been completed and the aircraft, engine, or related component has gone into service. These flaws are attributable to ag ing effects caused by either time, flight cycles, service operating conditions, or combinations of these effect s. The following are brief descriptions of some in-service flaws.
Stress corrosion cracks can develop on the surface of parts that are under tension stress in service and are also exposed to a corrosive environment, such as the inside of wing skins, sump areas, and areas between two metal parts of faying surfaces.
Overstress cracks can occur when a part is stressed beyond the level for which it was designed. Such overstressing can occur as the result of a hard landing, turbulence, accident, or related damage due to some unusual or emergency condition not anticipated by the designer, or because of the failure of some related structural member.
Fatigue cracks can occur in parts that have been subjected to repeated or changing loads while in service, such as riveted lap joints in aircraft fuselages. The crack usually starts at a highly-stressed area and propagates through the section until failure occurs. A fatigue crack will start more readily where the design or surface condition provides a point of stress concentration. Common stress concentration points are: fillets; sharp radii; or poor surface finish, seams, or grinding cracks.
Unbonds, or disbonds, are flaws where adhesive attaches to only one surface in an adhesive-bonded assembly. They can be the result of crushed, broken, or corroded cores in adhesive-bonded structures. Areas of unbonds have no strength and place additional stress on the surrounding areas making failure more likely.
Delamination is the term used to define the separation of composite material layers within a monolithic structure. Ultrasonic is the primary method used for the detection of delamination in composite structures.
SELECTING THE NDI METHOD. The NDI method and procedure to be used for any specific part or component will generally be specified in the aircraft or component manufacturer’s maintenance or overhaul manuals, SSID’s, SB’s, or in AD’s.
NOTE: Some AD’s refer to SB’s which may, in turn, refer to manufacturer’s overhaul or maintenance manuals.
Appropriate Method. The appropriate NDI method may consist of several separate inspections. An initial inspection may indicate the pr esence of a possible flaw, but other inspections may be required to confirm the original indication. Making the correct NDI method selection requires an understanding of the basic principles, limitations, and advantages and disadvantages of the available NDI methods and an understanding of their comparative effectiveness and cost.
Other Factors. Other factors affecting the inspection are:
The critical nature of the component;
The material, size, shape, and weight of the part;
The type of defect sought;
Maximum acceptable defect limits in size and distribution;
Possible locations and orientations of defects;