Par 4-91 Page 4-177
A- Slot Width (Original Tube).
B- Outside Diameter (Insert Tube).
C- Streamline Tube Length of Major Axis.
S.L. Size A B C 6A 1” .380 .560 1.340 .496 1-¼ .380 .690 1.670 .619 1-½ .500 .875 2.005 .743 1-¾ .500 1.000` 2.339 .867 2 .500 1.125 2.670 .991 2-¼ .500 1.250 3.008 1.115 2-½ .500 1.380 3.342 1.239
ROUND INSERT TUBE (B) SHOULD BE AT LEAST OF SAME MATERIAL AND ONE GAUGE THICKER THAN ORIGINAL STREAMLINE TUBE (C).
FIGURE 4-42. Streamline tube splice using round tube (applicable to landing gear).
shown in figure 4-35 through figure 4-45. However, it will always be necessary to ascertain whether or not the members are heat treated. The axle assembly as shown in figure 4-47 is, in general, of a nonrepairable type for the following reasons.
The axle stub is usually made from a highly heat-treated nickel alloy steel and carefully machined to close tolerances. These stubs are usually replaceable and must be replaced if damaged.
The oleo portion of the structure is generally heat treated after welding, and is perfectly machined to ensure proper functioning of the shock absorber. These parts would be distorted by welding after machining.
REPAIRS TO WELDED ASSEMBLIES. These repairs may be made by the following methods.
A welded joint may be repaired by cutting out the welded joint and replacing it with one properly gusseted. Standard splicing procedures should be followed.
Par 4-93 Page 4-178
A- Minimum Length of Sleeve.
B- Streamline Tube Length of Minor Axis.
C- Streamline Tube Length of Major Axis.
S.L. Size A B C 1” .572 .82 1.340 1-¼ .714 .476 1.670 1-½ .858 .572 2.005 1-¾ 1.000 .667 2.339 2 1.144 .762 2.670 2-¼ 1.286 .858 3.008 2-½ 1.430 .954 3.342
FIGURE 4-43. Streamline tube splice using split sleeve (applicable to wing and tail surface brace struts and other members).
Replacing weld deposit by chipping out the metal deposited by the welding process and rewelding after properly reinforcing the joint by means of inserts or external gussets.
STAINLESS STEEL STRUCTURE. Repair structural components made from stainless steel, particularly the “18-8” variety (18 percent chromium, 8 percent nickel), joined by spot welding, in accordance with the instructions furnished by the manufacturer, DER, or FAA.
Substitution of bolted or riveted connections for spot-welded joints are to be specifically approved by a DER or the FAA.
Repair secondary structural and nonstructural elements such as tip bows or leading and trailing edge tip strips of wing and control surfaces by soldering with a 50-50 lead-tin solder or a 60- 40 lead-tin solder. For best results, use a flux of phosphoric acid (syrup). Since the purpose of flux is to attack the metal so that the soldering will be effective, remove excess flux by washing the joint. Due to the high-heat conductivity of the stainless steel, use a soldering iron large enough to do the work properly.
Par 4-93 Page 4-179 INSERT TUBE IS OF SAME STREAMLINE TUBING AS ORIGINAL.
A- Is ²/³ B.
B- Is Minor Axis Length of Original Streamline Tube.
C- Is Major Axis Length of Original Streamline Tube.
S.L. Size A B C 6A 1” .382 .572 1.340 5.160 1-¼ .476 .714 1.670 6.430 1-½ .572 .858 2.005 7.720 1-¾ .667 1.000 2.339 9.000 2 .763 1.144 2.670 10.300 2-¼ .858 1.286 3.008 11.580 2-½ .954 1.430 3.342 12.880
FIGURE 4-44. Streamline tube splice using split insert (applicable to landing gear).
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.