CHAPTER 1. GENERAL INTRODUCTION. Over 80 percent of the inspections on large transport category aircraft are visual inspections. On small transport aircraft the ratio is even greater and on general aviation aircraft, virtually all inspection is visual. Visual inspection is usually the most economical and fastest way to obtain an early assessment of the condition of an aircraft and its components. Most of the defects found on aircraft are found by visual inspections, and the airframe manufacturers and users depend on regular visual inspections to ensure the continued airworthiness of their aircraft. Consequently, it is important that visual inspection methods be understood and properly applied by those responsible for the continued airworthiness of aircraft.
Proficiency in visual inspection is crucial to the safe operatior fairy earning her then eve eden one experiend bument describes those methods and the way they are used in the various inspections carried out on aircraft.
2. RELATION OF VISUAL INSPECTION TO NONDESTRUCTIVE INSPECTION (NDI).
Visual inspection is an essential part of airplane maintenance.
The visual inspection component of NDI requires trained and experienced inspection personnel, using validated procedures and appropriate calibration standards with effective, well-maintained equipment in a well-managed maintenance environment.
3. DEFINITION OF VISUAL INSPECTION. Visual inspection is defined as the process of using the eye, alone or in conjunction with various aids, as the sensing mechanism from which judgments may be made about the condition oi a unit to be inspected. imaging devices are playing an increasing part in the inspection process, (e.g., ultrasonic C-scans, eddy current imaging, realtime X ray). Analysis of such displays is not considered visual inspection and will be covered under image analysis in AC 43-X, Nondestructive Inspection For Aircrait.
1 Goranson, U.F. and Rogers, J.I., 'Elements of Damage Tolerance Verification," 12th Symposium of International Commercial Aeronautical Fatigue, Touluse, France, May 1983.
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4. PURPOSE OF VISUAL INSPECTION.
Visual inspection is used to:
• Provide an overall assessment of the condition of a structure, component, or system.
• Provide early detection of defects before they reach critical size.
• Detect errors in the manufacturing process.
• Obtain more information about the condition of a component showing evidence of a defect.
In many situations, no reliable alternative exists to visual inspection. Visual procedures are mandated by the FAA for structural inspections to support Supplementary Structural Inspection Documents (SSIDs), Service Bulletins (SBs), and Airworthiness Directives (ADS).
5. AIRFRAME AND ENGINE STRUCTURAL DETAILS.
a. Typical Airframe Defects. Typical airframe defects found in aircraft which can be detected by visual inspection can be divided into three types: cracks, corrosion, and disbonding. Other defects, such as system and component wear, accidental damage, environmental damage from long term storage, sunlight, etc., can also be detected visually.
(1) Cracks. Figure 1-1 illustrates areas most susceptible to cracks. Figure 1-2 shows typical surface cracks which can be detected by visual inspection. Surface cracks caused by fatigue are illustrated in Figure 1-3. An example of skincracking at fasteners is shown in Figure 1-4. Sometimes an underlying crack can cause a distortion which can be detected visu- Chap 1 Page 2 Par 4
Empennage General Condition:
Attach Points Engine Mount Attach Points Skin Doublers and Pressure Bulkheads On Pressurized Aircraft Landing Gear Fuel Tanks Wheel Rims Wing Spars and Caps Lower Wing Skins FIGURE 1-1. AREAS MOST SUSCEPTIBLE TO CRACKS Crack - Fastener removed FIGURE 1-2. TYPICAL SURFACE CRACKS Chap 1 Par 5 Page 3
EXTERML 3198
- STA.
58.159 FIGURE 1-3. MULTIPLE-SITE DAMAGE SURFACE FATIGUE CRACKS FIGURE 1-4. EXAMPLE OF SKIN-CRACKING AT FASTENERS
(2) Corrosion. Figure 1-5 illustrates areas most susceptible to corrosion. The various manifestations of corrosion such as missing rivet heads are shown in Figure 1-6.
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Passenger Floor Supports Cargo and and Flooring Crew Doors Galley Areas Under De-Icer Boots Areas in Path of Battery Exhaust Gasses Areas Lavatory Areas Undercarriage Bays Integral Fuel Tanks FIGURE 1-5. AREAS MOST SUSCEPTIBLE TO CORROSION FIGURE 1-6. EXAMPLE OF MISSING RIVET HEADS RESULTING
FROM CORROSION PRODUCTS An example of blistering of paint in a fuel cell caused by corrosion is illustrated in Figure 1-7. Chipped and loose paint on a Chap 1 Par 5 Page 5
wing skin is shown in Figure 1-8. Figure 1-9 shows internal corrosion of a tubular engine mount.
FIGURE 1-7. EXAMPLE OF BLISTERING OF SEALANT IN A FUEL CELL
CAUSED BY CORROSION FIGURE 1-8. EXAMPLE OF CHIPPED AND LOOSE PAINT ON A WING
SKIN CAUSED BY CORROSION Chap 1 Page 6 Par 5
8/14/97 AC 43-204 FIGURE 1-9. INTERNAL CORROSION OF THE TUBULAR ENGINE MOUNT OF A 1946 VINTAGE CESSNA (Courtesy of Shoreline Aviation, Marshfield Municipal Airport, MA) chap 1 Par 5 Page 7
corrosion of a rudder control cable and elevator rib are shown in Figures 1-10 and 1-11, respectively. Figure 1-12 shows an example of skin-bulging from corrosion of the faying surface between skin and internal structure around a cargo doorway. Figure 1-13 shows two examples of a nut which cracked from corrosion fatigue.
Figure 1-14 illustrates landing gear and wheel corrosion points.
FIGURE 1-10. CORROSION OF THE RUDDER CONTROL CABLE OF A 1969 CESSNA 172, FOUND VISUALLY (Courtesy of Shoreline Aviation, Marshfield Municipal Airport, MA) Chap 1 Page 8 Par 5
FIGURE 1-11. CORROSION OF THE ELEVATOR RIB OF A 1969 CESSNA 172, FOUND VISUALLY (Courtesy of Shoreline Aviation, Marshfield Municipal Airport, MA) FIGURE 1-12. EXAMPLE OF SKIN-BULGING DUE TO CORROSION Chap 1 Par 5 Page 9
FIGURE 1- 13. EXAMPLE OF CRACKED NUT DUE TO CORROSION (Courtesy of McDonnell Douglas) Chap 1 Page 10 Par 5
• TYPICAL DEBRIS TRAPS WADSY WELLS
SWITCHES
- STRUTS
TIE DOWN POINTS
UNPLATED HIGH
INSIDE AXLES STRENGTH STEEL
SPRINGS
• WATER TRAPS
DISSIMILAR METAL
CONTACTS
UNDER FERRULES AND IDENTIFIÇATION TAPES
WHEEL BEARING RACES FIGURE 1-14. LANDING GEAR AND WHEEL CORROSION POINTS (Courtesy of the U.S. Navy)
(3) It is very difficult to detect disbonding by visual means, since it is usually an internal condition and not likely to show up on the surface of an aircraft.
Figure 1-15 illustrates areas most susceptible to disbonding.
Wherever a bonded surface becomes disbonded, corrosion is likely to occur and may be detected visually.
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Composite Surfaces Multiple Element Wing Spar Assemblies
• Doublers Around Doors Skin Doublers FIGURE 1-15. AREAS MOST SUSCEPTIBLE TO DISBONDING during inspantion of ensire components. Fratientiv it is neces- Engine Defects. Figure 1-16 shows typical defects found sary to use visual aids to detect defects. Figure 1-17 illustrates typical defects seen through borescopes and other aids.
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