8/8/74 • AC 20-84 CHG 1
(14) Routine inspection disclosed a 2" crack in elevator hat section skin at station 173.21 and a 3" segment missing at station
99.79. IAI 7,628 hours.
(15) The upper rudder hinge fitting was found cracked at the lower lug, fitting P/N 65-23337-1. IAI 11,647 hours.
(16) The upper rudder tab actuating fitting was found cracked, P/N 65-6244-2. TAT 16,145 hours. On another aircraft, the lower rudder tab rod attach bracket was cracked, P/N 65-17483-7.
TAT 6,361.
Three cracks in the 0/B panel of the R/H horizontal stabilizer spar and one crack in the I/B panel of the L/H horizontal stabilizer spar were found during routine inspection, TAT 6,706 hours.
(18) The L/H horizontal stabilizer spar flange was found cracked at station 208. TAT 8,816 hours.
* d. Landing Gear.
(1) Inspection found #3 MLG wheel inner half broken. The inner bearing and hub were separated from the wheel half. ISN 3,925 hours.
(2) When lowering landing gear during approach, crew heard loud bang. Inspection after landing revealed the R/H landing gear retract cylinder and walking beam protruding through top of wing. Operator reported probable cause as failure of beam, P/N 65-17658-11.
describes installation of new steel beam.
(3) During scheduled inspection, the L/H MLG walking beam was found to be cracked at the 0/B aft attach lug, P/N 65-17658-11.
TAT 9,891 hours. Service Bulletin 32-167 describes installation Par 8 Page 9
22 Jan 73 AC 20-84 Appendix l APPENDIX 1. CORROSION
1. CAUSES OF CORROSION.
a. Metal corrosion is the deterioration of the metal by chemical or electrochemical attack. Corrosion can take place internally as well as on the surface of the metal. This deterioration may change the smooth surface, weaken the interior, or damage or loosen adjacent parts.
Water or water vapor containing salt and combined with oxygen in the atmosphere produces main source of corrosion in aircraft. Thus, aircraft operating in a marine environment or in areas where the atmosphere contains industrial fumes which are corrosive are particularly susceptible to corrosive attacks. If unchecked, corrosion can cause eventual structural failure.
2. TYPES OF CORROSION. There are two general classifications of corrosion, direct chemical attack and electrochemical attack. In both types, the metal is converted into an oxide, hydroxide, or sulfate. The corrosion process involves the anode which is oxidized and cathode (or the corrosive agent) which is reduced.
a. Direct chemical attack. Corrosion by direct chemical attack results from direct exposure to caustic liquids or vapors. The anodic and cathodic change occurs at the same point. Direct chemical attack in aircraft structure deposits are caused by (1) spilled battery acid or fumes, (2) residual flux deposits from welds, and (3) trapped caustic cleaning fluids.
Electrochemical attack. An electrochemical attack is similar to the electrolytic reaction in electroplating or in a dry cell battery. The reaction requires a medium, like moisture, capable of conducting electricity. When a metal comes in contact with a corrosive agent (dissimilar metal) and is connected by a liquid path, the metal decays or corrodes. The electrochemical attack is responsible for most forms of corrosion on aircraft structure.
3• FORMS OF CORROSION. There are many forms of corrosion which depend on the metal involved, size, shape, atmospheric conditions and corrosion producing agents.
a. Surface corrosion. This may be caused by either direct chemical or electrochemical attack. Surface corrosion appears as a general roughening, or pitting of the surface of a metal accompanied by a powdery deposit of corrosion products.
b. Dissimilar Metal Corrosion. Extensive pitting damage may result from contact between dissimilar metal parts in the presence of a conductor.
A galvanic action like electroplating occurs at points of contact when insulation has broken down or was omitted.
Par 1 Page 1
AC 20-84 22 Jan 73 Appendix 1 Intergranular corrosion. The grain boundaries of an alloy are attacked by this type of corrosion. Intergranular corrosion may is a flaking of the metal at the surface caused by pressure of corrosion residual product buildup.
d. Stress corrosion. This type corrosion occurs as the result of the combined effect of tensile stresses and corrosive environment. Stress corrosion is found in most metals. However, it is a particular characteristic of aluminum, certain stainless steels and high strength steels.
e. Fretting corrosion. This occurs when two mating surfaces are subject to relative motion although normally at rest with respect to each other. It is characterized by surface pitting and generation of finely divided debris.
4. FACTORS AFFECTING CORROSION. Many factors affect the speed, cause, type, and seriousness of metal corrosion which include:
a. Climate.
b. Size and type of metal.
c. Foreign material.
5. CORROSION PREVENTION. Corrosion-preventive maintenance includes:
a. An adequate cleaning.
b. Thorough periodic lubrication.
c. Detailed inspection for corrosion and failure of protective systems.
d. Prompt treatment of corrosion and touchup of damaged paint areas.
e. Keeping drainholes free of obstruction.
f. Daily wipedown of exposed critical areas.
g. Sealing of aircraft against water during foul weather and proper ventilation on warm, sunny days.
h. Making maximum use of protective covers on parked aircraft.
Page 2 Par 3
Appendix 2 APPENDIX 2. STATION CHARTS 3° DIHEDRAL 3° ANHEDRAL 1080* 3510н -1810".
(133'-2" for -100) 1440" -3" for -100) 136°2" for - 100) 153°2 63°3~ (116'-2" Figure 1. Principal Dimensions Page 1
Appendix 2 WL 246.10 & WINDOWS UPPER RADII FLOOR I FOR OF CONSTANT FWD SECTION CONSTANT DOOR 30 x 60 (RH AND LH SIDE) WL303.5 REAR VIEW 200 ONLY 48 (REF) F200 ONLY 000000 232.. WL 148.5 WL 138.5 WAR SURFACE CARGO DECK SECTION 43 1070 SERVICE WINDOWS (TYP) WL 208.1 • DOOR -200 GALLEY DOOR -100 ONLY CARGO DOOR 200 ONLY CARGO SECTION - 100 ONLY
LEFT SIDE VIEW CARGO DOOR ONLY SIDEL 200 ONLY GALLEY DOOR 33 x 65 (AH SIDE) GEAR WELL 351.2 ELEESS DOOR MAIN WHEEL WELL DOOR -200 ENTRY DOOR 303 BEAN
204.5 249 259 277 . 7 251.6 SECTION WCI KEEL
219.8 235.8 FORWARD EMERGENCY EXIT AND RIGHT
196.5 203.8 DOOR 188 178 130- (20 x 38) LEFT SIDE Page 2 Figure 2, Forward Body Station Diagram
1/31/75 1586.91 / - STABIUZER HINGE POINT STA
REMOVABLE
PRODUCTION BEAM
JOINT FIN STA FIN STA
133.8. 157.2.
= 92.5
FIN STA REMOVABLE • 110.• • ID SPAR STA IM0L.00 STA 1110.00 STA 1130.00 LEADING EDGE FIN STA -- STABILIZER ACTUATOR
DUCT HOUSING FIN STA' PIVOT POINT
55.9 & AFT ENGINE AIR INLET DUCT ACCESS PANEL BUODER UPPER OUCT HOUSING
- RUDDER
HINGE POWTS IPPER 18 PLACES!
TORQUE BOX LOWER RUDDER UPPER
AIR STAIR WELL TORQUE
- 87.5 •Ox
- STRUT ATTACH - SIDE ENGINE ATTÄCH PORTS WL 232.5 -AFT ENGINE POINTS - STA 0.00 STRINGERS ITYPI - STA 1009.58 STA 1064.15 STA 1523.1 LOWER TORQUE LOWER TORQUE BOX • - 1901 AFT AMSTAIRS - S0x 20 B
• FIREWALL STA 118Ù STA 1D3 TANT STA 1203 STA 13 Appendix 2 AC 20-84
Page 4 CENTER SECTION ACCESS WOL •- FSS 1068 LEADING EDGE TYP FSS INBO san SEOB1ÃO INBO 3325 Appendix 2 AC 20-84 CHG 2 FLAP HOSTA
SEE DETAIL A FRONT SPAR BREAK 500 Salo DEFUEL VALVE WBL 252.075 Figure 4. Wing Stalion Diagram ACCESS JANK ACCESS- 500% 5L FUELING ACCESS
DETAIL A FUEL ACCESS 20 0
TANK ENDS
166.95 / ACCESS
LG TRUNNION E
LEADING EDGE NO LANDING GEAR SUPPORT BEAM NO 8 NO SLAT NO
70.507 SPOILER *BLO
203.0
TRAILING EDGE INBOARD FLAPI
INDOARD AILERON
s.0
OUTBOARD FRAP ₩2.0 VENT 1/31/75
TANK END
OUTRONAD ALLERON
Appendix 2
184.40
138.30
101.42 TAB HINGE POINTS
• 55.92 STATION D
•18 44 29.361 STAB HINGE REAR SPAR ~ AIMPLANE - CONTROL TAB HINGE E EDGI LEADING STATION O 53.91 CONTROL TAB
66.50 STABILIZER STATION O LEADING EDGE 118.15 & INBOARD REAR SPAR THEORETICAL TRAILING EDGE STAB STA 78.13
136.50
210.00 § FRONT SPAR STA ELEV § ELEVATOR HINGE STAB STA 151.81
209.96 STA 188.65
6.00
7.38 5.00 - → 40.59
174.69
- 55.35
73.80 Figure 5, Stabilizer and Elevator Station Diagram Page 5
1/31/75 218.7 SIDE VIEW STA NAC E AFT MOUNT RING. NAC FWD RIN @ FWD MOUNT UP
COWL SPLIT € ENGINE COWL SPLIT.
BWL 239.7 ENGINE STRUT • INLET NAC WL 100.0 Figure 6. Side Engines Station Diagram 21Q3 STA NAC
218.7 STA 1257.4 STA
NAC B STA ENG NAC TOP VIEW 136.0 99.3
STA STA NAC NAC ENG ENG IN B
RING E AFT MOUN MOUNT RING - COWL SPLIT FWD
408.3 COWL SPLIT BBL 5L Q.9_ VAC BLO - € ENGINE E (BL O) = INLET NAC
25.1 BBL 14.. FIREWALI BBL 81.0 EBL AC 20-84 CHG 2 STRUT FRONT SPAR BBL 70.
Appendix 2 BBL 62.0 03.5
STRUT REAR SPAR STA 1243.0 NAC •: AC 1247.5 B STA B STA 1183 102.5 1140.3 Page 6 STRUT & BODY CONTOR LINE 6 STA 1175.0 HAC
Appendix 3 APPENDIX 3. NONDESTRUCTIVE TESTING
1. MAINTENANCE TOOL. Simply stated, nondestructive testing (NDI) is a tool for performing maintenance inspection. This includes utilization of such maintenance tools as X-ray, ultrasonic, magnetic particles, eddy * current, dye penetrant, and visual with or without magnification.
Maintenance Inspection. NDI permits maintenance inspection without removing components from aircraft or tearing down complex assemblies.
Defects in various aircraft systems which would escape detection through normal visual inspection will be identified by NDT.
Training Required. Special NDT training is desirable to make sure that the technician is capable of operating the equipment and interpreting the results. Also, many States require that an X-ray technician have an approved certificate for use of X-ray in industrial applications. This is to minimize improper use of X-ray equipment
2. METHODS AND APPROACHES FOR DAMAGE DETECTION. Information on the application of NDI methods for the detection of fatigue damage is scattered through literature on metal fatigue and literature on NDI. Few publications deal with this problem specifically. Some publications are limited to laboratory investigations, and the NDT application is conducted under controlled laboratory conditions. Such investigations contribute considerably to available knowledge and provide new or improved NDI methods for field use. However, there is a great difference between what can be done in the laboratory and what can be used in practical
3. NDI METHOD IN FIELD AND SERVICE USE. Most of the NDT methods that are used under field and service conditions are those capable of detecting fatigue cracks of various sizes. These methods are described in books on the subject of nondestructive testing and other publications such as reports, technical papers, and magazine articles. The NDT methods most commonly used in the field and service for fatigue crack detection follow.
4. VISUAL INSPECTION. Visual inspection is the oldest, simplest, cheapest, and most widely used of all NDT methods. The basic principal used in visual inspection is to illuminate the object and examine the surface with the eye.
a. The surface should be adequately cleaned before being inspected.
Visual inspection for detection of fatigue cracks can be improved by aids such as mirrors, lenses, microscopes, periscopes, and telescopes. These devices compensate for limitations of the human eye. Boroscopes permit direct visual inspection of the interior of hollow tubes, chambers, and other internal surfaces.
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AC 20-84 22 Jan 73 Appendix 3 The capability of visual inspection to detect a fatigue crack depends on many factors such as the size and location of the crack, the illumination used, optical aids employed, and skill of the inspector.
is often difficult to detect even a relatively large fatigue crack that is located, for example, at the corner of a groove or that coincides with a machining mark. There are, of course, also limitations on the size of cracks that can be detected by visual inspection, depending on optical aids employed.
LIQUID PENETRANT. The liquid penetrant is one of the oldest methods of nondestructive testing and is capable of detecting cracks that may be impossible to find with the most careful visual inspection because either they are too small or because they are difficult to detect due to their location. The principle involves applying to the part surface a liquid penetrant having a low-surface tension and low viscosity. When used on a clean surface that the liquid will wet, the liquid is drawn into the cracks by capillary action, The presence of the liquid in the cracks is revealed when, after wiping the excess liquid from the surface, a developer is applied that acts like a blotter and draws the liquid out.
a. There are two types of liquid penetrants in general use. One contains a dye which usually gives a good color contrast against the selected developer; the other contains dissolved fluorescent material, which makes it readily visible when viewed under a "black" (ultraviolet) light.
b. Liquid penetrant inspection is inexpensive and readily applicable to field use. The surface must be cleaned before inspection and also afterwards to remove the developer.
6. MAGNETIC METHODS. Magnetic inspections are used to detect surface or near surface discontinuities in ferromagnetic materials, and they are well suited for the detection of fatigue cracks.
a. The principle employed here is that once a magnetic field is induced in a material, any cracks and flaws that are present, will perturb or distort that magnetic field. These methods are most sensitive when the crack orientation and the magnetic field direction are perpendicular to each other. When they are parallel, the crack will not be detected.
b. The magnetic particle method is the most frequently used. It consists of three basic steps:
(1) Establishment of the magnetic field in the part to be inspected.
(2) Application of magnetic particles to the surfaces of the part.
(3) Visual examination of the surfaces for indications of fatigue cracks. These indications are provided by the particles being Page 2 Par 4
22 Jan 73 AC 20-84 Appendix 3 attracted to the locations of the cracks (or other defects) due to local variations in the magnetic field that are produced.
Iwo classes of magnetic particles are available. The wet method particles use a liquid vehicle; the dry method particles are borne by air. These particles are usually:
(1) Colored to give contrast with the surface being inspected, or
(2) Coated with fluorescent material to make them readily visible under black light. Parts inspected by magnetic particle methods must be cleaned.
7. RADIOGRAPHY. Radiography is a method of nondestructive testing which uses X-ray gamma, beta, or neutron radiation. It is based on the ability of these radioactive sources to penetrate materials. The intensity of the penetrating radioactivity is modified by passage through materials and by defects in the material. These intensity changes are recorded on film as areas of varying density (or darkness) which permits distinguishing flaws and cracks. Obviously, maximum sensitivity occurs when the crack is oriented such that its longest dimension is parallel to the direction of radiation.
a. X-ray radiography has two main advantages; (1) versatility, and
(2) sensitivity. The X-ray energy source can be easily adjusted for variations in thickness. It is also adaptable to fluoroscopy and television systems.
The advantages of gamma radiography are: (1) portability, and
(2) a relatively low cost.Portability comes from the fact that the source is small. This permits its effective use in the field particularly in remote areas. One of the difficulties with the gamma radioactive source is that the source cannot be varied or turned off so that safety precautions must be observed at all times. (X-ray constitutes a health hazard only during operation of the X-ray equipment.)
c. Conventional radiography is firmly established and reasonably easy to understand. One of the original drawbacks was the long time involved in the developing and processing of film. This has been overcome by modern automatic film processing techniques.
Interpretation of the processed film is the most important phase of radiography. Adequate tools such as a film illuminator lens and good working conditions should be available to assist the interpreter in detecting cracks in the part displayed on the film.
8. ULTRASONICS. Ultrasonic methods have received wide acceptance in the aviation industry and are particularly useful for determining the integrity of a member of a structure. Basically, sound energy above the audible range is transmitted into a part, and a signal is received and analyzed.
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