VISUAL INSPECTION FOR AIRCRAFT

Advisory U.S. Department of Transportation CircularFederal Aviation Administration Subject: VISUAL INSPECTION FOR Date 8114/97 AC No: 43-204 AIRCRAFT Initiated by: AFS-350 Change: 1. PURPOSE. This advisory circular (AC) provides technical in formation to persons conducting a visual inspection of aircraft. The procedures presented in this AC are an acceptable means, butnot the only acceptable means, for conducting visual inspections and inspection programs. Where the aircraft, engine, propeller,or appliance manufacturer has published a recommended inspection schedule or program for a particular aircraft, that program should take precedence over the recommendations of this AC. 2. RELATED READING MATERIAL. a. AC 20-37D, Aircraft Metal Propeller Maintenance. b. AC 43-3 t Nondestructive Testing in Aircraft. c. AC 43-4A, Corrosion Control for Aircraft. d. AC 43-7, Ultrasonic Testing for Aircraft. e. AC 43-12A, Preventive Maintenance. f. AC 43.13-1A, Acceptable Methods, Techniques and Practices--Aircraft Inspection and Repair. Richard 0. Gordon Acting Deputy Director, Flight Standards Service 8/14/97 3 CONTENTS CHAPTER 1. GENERAL 1. INTRODuCTION. 1 2. RELATION OF VISUAL INSPECTION TO NONDESTRUCTIVE 1 3. DEFINITION OF VISUAL INSPECTION. 1 4. PURPOSE OF VISUAL INSPECTION. 2 5. AIRFRAME ~nD ENGINE STRUCTURAL DETAILS. 2 6. FACTORS AFFECTING VISUAL INSPECTION. 17 7. SAFETY. 19 8. THE VISUAL INSPECTION PROCESS. 199. VISUAL INSPECTION! GENERAL. 2 10. AIRFRAME VISUAL INSPECTION. 21 11. ENGINE VISUAL INSPECTION. 24 12. INSPECTION FOR SPECIFIC TYPES OF CORROSION. 24 13.-199. RESERVED. 31 CHAPTER 2. VISUAL INSPECTION PROCEDURES 3 200. GENERAL. 3 201. MATERIAL CONTAINED IN A VISUAL INSPECTION PROCEDURE. 3 202. ACTIVITIES APPLYING TO ALL VISUAL INSPECTIONS. 4 203. RECORD KEEPING. 5 204. FOUR LEVELS OF VISUAL INSPECTION. 47 205. ACCEPTABLE PRACTICE FOR VISUAL INSPECTION. 206.-299. RESERVED. 5 CHAPTER 3. VISUAL INSPECTION AIDS 63 300. GENERAL. 63 301. LIGHTING AND ILLUMINATION. 63 302. LIGHTING SYSTEMS. 100 303.-399. RESERVED. 104 CHAPTER 4. EQUIPMENT USED IN VISUAL INSPECTION 117 400. GENERAL. 117 401. MAGNIFYING DEVICES. 120 402. PHOTOGRAPHIC AND VIDEO SYSTEMS. 120 403. OPTICAL COMPARATORS. 126 404. BORESCOPES. 127 405. LIST OF EQUIPMENT USED IN VISUAL INSPECTION. 156 406.-499. RESERVED. 156 CHAPTER 5. DEFINITIONS 167 500. DEFINITIONS. 167 501.-599. RESERVED. 173 i 3-20 8/14/97 APPENDIX BEACHCRAFT, PROCEDURE ATA CODE 57-10, SAMPLE INSPECTION APPENDIX B. BEACHCRAFT, PROCEDURE ATA CODE 55-30, SAMPLE INSPECTION APPENDIX C. P~~TT & WHITNEY, ENGINE GENERAL--I~SPECTION/CHECK -00 S&MPLE INSPECTION PROCEDURE APPENDIX D. PRATT -01A, & WHITNEY, ENGINE GENERAL--INSPECTION/CHECK SAMPLE INSPECTION PROCEDURE APPENDIX E. DC-9 SERVICE BULLETIN, SAMPLE INSPECTION PROCEDURE APPENDIX F. BOEING 747 SERVICE PROCEDURE BULLETIN, SAMPLE INSPECTION APPENDIX G. VISUAL INSPECTION EQUIPMENT APPENDIX H. ENGINE VISUAL INSPECTION GLOSSARY LIST OF ILLUSTRATIONS Page No. FIGURE 1-1. AREAS MOST SUSCEPTIBLE TO CRACKS 3 FIGURE 1-2. TYPICAL SURFACE CRACKS 3 FIGURE 1-3. MULTIPLE-SITE DAMAGE SURFACE FATIGUE CRACKS 4 FIGURE 1- EXAMPLE OF SKIN-C~~CKING AT FASTENERS 4 FIGURE 1-5. AREAS MOST SUSCEPTIBLE TO CORROSION 5 FIGURE -6. EXAMPLE OF MISSING RIVET HEADS RESULTING FROM CORROSION PRODUCTS 5 FIGURE 7. EXfu~PLE OF BLISTERING OF SEALANT IN A FUEL CELL CAUSED BY CORROSION 6 FIGURE 1-8. EXAMPLE OF CHIPPED k~D LOOSE PAINT ON A WING SKIN CAUSED BY CORROSION 6 FIGURE 1-9. INTERNAL CORROSION OF THE TUBULAR ENGINE MOUNT OF A 1946 VINTAGE CESSNA 7 FIGURE 1 10. CORROSION OF THE RUDDER CONTROL CABLE OF A 1969 CESSNA 172, FOUND VISUALLY 8 FIGURE 1-11. CORROSION OF THE ELEVATOR RIB OF A 1969 CESSNA 172, FOUND VISUALLY 9 FIGURE 1-12. EXAMPLE OF SKIN-BULGING DUE TO CORROSION 9 FIGURE 1-13. EXAMPLE OF CRACKED NUT DUE TO CORROSION 10 FIGURE 1-14. LANDING GEAR AND WHEEL CORROSION POINTS 11 FIGURE 1-15. AREAS MOST SUSCEPTIBLE TO DISBONDING 12 FIGURE 1-16. COMMON PHYSICAL CHARACTERISTICS OF ENGINE DEFECTS (3 SHEETS) 13 FIGURE 1-17. TYPICAL DEFECTS AS SEEN THROUGH BORESCOPE AND OTHER AIDS 16 FIGURE 1-18. USING A FLASHLIGHT TO INSPECT FOR SURFACE CRACKS 22 ii 8/14/97 c FIGURE 1-19. UNIFORM ETCH CORROSION FIGURE 1-20. PITTING CORROSION FIGURE 1-21. GALVANIC CORROSION OF MAGNESIUM F~JACENT TO STEEL FASTENER FIGURE 1-22. CONCENTRATION CELL CORROSION FIGURE 1-23. INTERGRANULAR CRACKING AND CORROSION ON A WINGSPAR CHORD FIGURE 1-24. SEVERE EXFOLIATION CORROSION FIGURE 3-1. EXAMPLE OF THE EFFECT OF SHINY AND MATTE FINISH OF PARTS AND LIGHTING SYSTEM ORIENTATION ON SEEING TASKS FIGURE 3-2. EXAMPLE OF THE EFFECT OF LIGHTING SYSTEMS ON INSPECTION OF A CIRCUIT BOARD FIGURE 3-3. EXAMPLE OF THE EFFECT OF LIGHTING SYSTEM ORIENTATION ON AN INSPECTION SURFACE FIGURE 3-4. EXAMPLES OF DIRECT AND REFLECTED GLARE FIGURE 3-5. EXAMPLE OF LUMINAIRE SHIELDING ANGLE FIGURE 3-6. HARSH SHADOWS PRODUCED BY UNIDIRECTIONAL ILLUMINATION (LEFT) F~D SOFT SHADOWS PRODUCED BY DIFFUSE ILLUMINATION FIGURE 3-7. MULTIPLE SHADOWS (UPPER LEFT) ARE CONFUSING; SINGLE SHADOWS HELPi DIFFUSED SHADOWS (CENTER) MAY CONFUSE, BUT CP~ LIGHT (LOWER RIGHT) ERASES THE 80 FIGURE 3-8. CORRELATED COLOR TEMPERATURE IN KELVINS OF SEVERAL ELECTRIC LIGHT AND DAYLIGHT SOURCES 82 FIGURE 3-9. INTERNATIONAL COMMISSION ON ILLUMINATION LUMINAIRE CLASSIFICATIONS FOR GENERAL LIGHTING 83 FIGURE 3-10. TYPICAL LAMP AND FIXTURE LIGHT DISTRIBUTION CURVES 84 FIGURE 3-11. ILLUSTRATION OF THE IMPORTANCE OF A WHITE CEILING FOR IMPROVING THE VISUAL ENVIRONMENT OF AN INDUSTRIAL FACILITY 85 FIGURE 3-12. EXAMPLES OF PLACEMENT OF SUPPLEMENTARY LUMINAIRES 87 FIGURE 4-1. TYPICAL 35MM CAMERA AND CAMERA ADAPTER INSTALLATION ON A RIGID BORESCOPE 121 FIGURE 4-2. TYPICAL BORESCOPE VIDEO ADAPTER SYSTEM 122 FIGURE 4 3. BLOCK DIAGRAM OF A TYPICAL VIDEO INSPECTION SYSTEM 123 FIGURE 4-4. SCOPEMAN HAND-HELD VIDEO MICROSCOPE IMAGING SYSTEM 12 FIGURE 4-5. SMARTSCOPE VIDEO MEASURING MICROSCOPE SYSTEM 125 FIGURE 4-6. SCHEMATIC OF AN OPTICAL COMPARATOR 126 FIGURE 4-7. TYPICAL OPTICAL COMP&~TOR 127 FIGURE 4-8. THREE TYPICAL DESIGNS OF BORESCOPES 12 FIGURE 4-9. TYPICAL DIRECTIONS AND FIELD OF VIEW OF RIGID BORESCOPES 129 FIGURE 4-10. TYPICAL MICRO-BORESCOPE 133 FIGURE 4-11. TYPICAL EXTENDIBLE BORESCOPE 134 FIGURE 4-12. TYPICAL SCANNING BORESCOPE 135 FIGURE 4-13. ZOOM-A-BORE INSPECTION INSTRUMENT WITH MAGNIFICATION BOOSTER ATTACHED 136 3-2 8/14/97 FIGURE 4-1 . CRO-BORE VIEWING SYSTEM 137 - ~. TUBE VIEWING SYSTEM 139 FIGURE -16. DEEP-HOLE MIRROR VIEWING SYSTEM 140 FIGURE -17. TYPICAL FLAWS SEEN THROUGH A FLEXIBLE FIBERSCOPE 141 FIGURE -18. COMPARISON VIEWS WITH DIFFERENT QUANTITIES OF FIBERS IN THE FIBERSCOPE IMAGE BUNDLE 143 FIGURE -19. FLEXIBLE VIDEOSCOPE IMAGES 144 FIGURE -20. TYPICAL CCD VIDEOSCOPE RESOLUTION 145 FIGURE -21. COMP~RISON BETWEEN VIDEOSCOPE AND FIBERSCOPEIMAGES 146 FIGURE -22. VIEW THROUGH A MEASURING FIBERSCOPE 147 IGURE -23. RETRIEVAL DEVICE IN BORESCOPE WORKING CH~NNEL 148 IGURE 4-24. FLYING PROBE FLEXIBLE BORESCOPE 151 FIGURE 4-25. VIDEOHOOK PROBE ATTACHMENT FOR A FLEXIBLE BORESCOPE 152 FIGURE 4-26. POWER BLENDING BORESCOPE KIT 153 FIGURE 4-27. MEASURING SYSTEM 154 LIST OF TABLES Page No. TABLE 1-1. ILLUMINA~CE LEVELS FOR SAFETY* 18 TABLE 2-1. TOPICS TO BE CONSIDERED IN PREPARING OR REVIEWING VISUAL INSPECTION PROCEDURE 44TABLE 3-1. ILLUMINANCE VALUES 65TABLE 3-2. WEIGHTING FACTORS TO BE CONSIDERED IN SELECTING SPECIFIC ILLUMINANCE WITHIN RANGES OF VALUES FOR EACH ILLUMINANCE CATEGORY 66TA~LE 3-3. IES RECOMMENDED ILLUMINANCE CATEGORIES FOR THE DESIGN AND EVALUATION OF LIGHTING SYSTEMS FOR INDUSTRIAL INSPECTION AREAS 67TABLE 3-4. CLASSIFICATION OF VISUAL TASKS AND SUPPLEMENTARY LIGHTING TECHNIQUES (3 SHEETS) 71TABLE 3-5. RECOMMENDED REFLECTANCE VALUES FOR INDUSTRIAL LIGHTING 78TABLE 3-6. RECOMMENDED MAXIMUM LUMINANCE RATIOS FOR INDUSTRIAL LIGHTING 81TABLE 3-7. TYPICAL PORTABLE LUMINAIRES FOR SUPPLEMENTARY LIGHTING (7 SHEETS) 89TABLE 3-8. TYPICAL INSPECTION FLASHLIGHTS (5 SHEETS) 96 TABLE 4-1. TYPICAL INSPECTION MIRRORS 117 TABLE 4-2. TYPICAL SIMPLE MAGNIFIERS 119TABLE -3. TYPICAL WORKING Ca~NNEL DEVICES 149 8/14/97 3-20 CHAPTER 1. GENERAL 2. enced propriate equipment 3 . inspection fined as the process unction with various may be made about ing devices are process, (e.g. , c C-scans, time X ray) . is of displays is inspection be covered under image 43-X, Nondestructive Inspection For 1 Goranson, U.F. , J.T., Elements of Damage Tal erance Verif ion," Symposium of International Commerc Aeronautical Fat , France, May 1983. Chap 1 Par 1 1 AC 43-204 8/14/97 4. PURPOSE OF VISUAL INSPECTION. Visual inspection is used to: • Provide an overall assessment of the condition of a struc ture, 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 in spection. Visual procedures are mandated by the FAA for struc tural inspections to support Supplementary Structural Inspection Documents (SSIDs) , Service Bulletins (SBs) , and Airworthiness Di rectives (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 di vided into three types: cracks, corrosion, and disbanding. 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 suscep tible 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 skin cracking at fasteners is shown in Figure 1-4. Sometimes an un derlying crack can cause a distortion which can be detected visu ally. Chap 1 Page 2 Par 4 8/14/97 AC 43-204 Empennage General Coi<:Iltion: Attach Points Skin Doublers and Pressure Bulkhead s On Pre,..urlzed Aircraft Fu el Tanks Wiog Spars aod CapsLower Win~r Skins FIGURE 1-1 . AREAS MOST SUSCEPTIBLE TO CRACKS FIGURE 1-2. TYPICAL SURFACE CRACKS Chap 1 Par 5 Page 3 AC 43 -2 04 8/14/97 ,.-·--·--· ,, FIGURE 1-3. MULTIPLE- SITE DAMAGE SURFACE FATIGUE CRACKS · 0 · • .(J F I GURE 1 - 4. EXAMPLE OF SKIN-CRACKING AT FASTENERS (2) Corrosion. Figure 1-5 i l lustrates areas mos t sus ceptible to corrosion. The various mani festations of corros i on such as miss i ng r i vet heads are shown in Figure 1-6. Chap 1 Page 4 Par 5 8/14/97 AC 43 - 204 Fl oor Sup ports and Flooring Lavatory .v.ou Underc.arriage Bays lntegl"3J Fuel Tanks FIGURE 1-5. AREAS MOST SUSCEP TI BLE 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 corro sion is illustrated in Figure 1- 7. Chipped and loose paint on a Chap 1 Par 5 Page 5 AC 1.13-201.1 8/14/97 wing skin is shown in Figure 1-8. Figure 1-9 shows internal cor rosion of a tubular engine mount. FIGURE 1-7. EXAMPLE OF BLISTERING OF SEALANT IN A FUEL CELL CAUSED BY CORROSION ~II 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, MarshfieldMunicipal Airport, MA) Chap 1 Par 5 Page 7 43-204 8/14/97 Corrosion of a rudder control cable and elevator rib are shown in Figures 1-10 and 1-11, respectively. Figure 1-12 shows an exam ple 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 8/14/97 AC 43-204 FIGURE 1-11. CORROSION OF THE ELEVATOR RIB OF A 1969 CESSNA 172, FOUND VISUALLY (Courtesy of Shoreline Aviat i on, Marshfield Municipal Airport, MA) FIGURE 1-12. EXAMPLE OF SKIN- BULGING DUE TO CORROSION Chap 1 Par 5 Page 9 AC 43-204 8/14/97 FIGURE 1- 13. EXAMPLE OF CRACKED NUT DUE TO CORROSION (Courtesy of McDonnell Douglas) Chap 1 Page 10 Par 5 8/14/97 AC 43-204 FIGURE 1-14. LANDING GEAR AND WHEEL CORROSION POINTS (Courtesy of the U.S. Navy) (3) It is very difficult to detect dis- bonding by visual means, since it is usually an internal condi tion and not likely to show up on the surface of an aircraft. Figure 1-15 illustrates areas most susceptible to disbanding. Wherever a bonded surface becomes disbanded, corrosion is likely to occur and may detec Chap 1 Par 5 Page 11 3-20 8/14/97 FIGURE 1-15. AREAS MOST SUSCEPTIBLE TO DISBONDING b. defects found insp of ection engine components. ly it is neces sary to use visual to detect defects. Figure 1-17 illustrates cal defects seen through borescopes and other aids. Chap 1 12 Par 5 8/14/97 3-20 FIGURE 1-16. COMMON PHYSICAL CHARACTERISTICS OF ENGINE DEFECTS (Sheet 1 of 3) (Courtesy of Pratt & Whitney) Chap 1 Par 5 13 IGURE 1-16. COMMON PHYSICAL CHAR~CTERISTICS OF ENGINE DEFECTS 2 of 3) Chap 1 Par 5 FIGURE 1-16. COMMON PHYSICAL CHARACTERISTICS OF ENGINE DEFECTS (Sheet 3 of 3) Chap 1 Par 5 15 AC 43-204 8/14/97 FIGURE 1-17. TYPICAL DEFECTS AS SEEN THROUGH BORESCOPE AND OTHER AIDS (Courtesy of McDonnell Douglas) Chap 1 Page 16 Par 5 8/14/97 43-2 6 . visual effect potential cause a. Inspection Personnel Qualifications and Training. In spection personnel should posses experience and knowledge of the origins and causes fects in raw manufacturing proc esses, the reshaping redi ion of se defects sub sequent part manufacturing processes, and fects that develop after the is put Inspection personnel should also have a working knowl of part component, or aircraft being inspected. It is essent inspection personnel be knowledgeable concerning the structural detail being evaluated to enable them to properly ify, and evaluate aircraft defects. Persons who inspect, approve, and return to service an aircraft appliance or part, must be certif in accordance the appropriate FARs or the work under a certificate holder who is charge of person. b. Inspection Area Access. Ease of access to the inspection area is important in obtaining reliable visual inspection re sults. Access consists of the act of getting into an inspection posit (primary access) inspect (secondary access) . Unusual i.e., crouching, lying on back, and overhead ) examples of difficult ac cess. (1) The necessity to get both hands structure le a f mirror or reaching awkward openings can tor's motivation, attitude, decision-making, to in terpret what is seen. (2) Staging equipment (e.g., forms, ladders, stools to permit access to the airframe and engines should be used , i.e., secured manually or engaged to prevent slips and ls. Protection should be pro vided to prevent potent injury from sharp edges and fts heavy weights. Adequate protection from ls should be provided wherever possible, such as lings and harnesses and lanyards on high working platforms. c. Lighting. Adequate and of illuminance and elimination of direct glare, reflected glare, and ows all enhance identification of defects. Conversely, ex cessive visual fatigue the delayed eye ion experienced when moving from bright surroundings into dark ones and vice versa could reduce effect detection of s. (1) Il should pro vided during occupancy of spaces that possess limi access. In Chap 1 Par 6 Page 17 43-204 8/14/97 those areas which fixed 1 and vehi cle mounted 1 (2) Excessive Glare. Uncontrol large differences of illumination and excessive glare should be avoided. Appropriate guides to limiting glare and adaptation effects are discussed in Chapter 3 of this AC and in the Illumination Engineering Society (IES) handbooks on lighting. (3) Lighting and Safety. Some accidents which have been attributed to an individual's care sness could have been par tially due to poor lighting. Illumination ls regarded as ab solute minimums for safety alone have been developed by the IES and are listed Table 1-1. TABLE 1-1. ILLUMINANCE LEVELS FOR SAFETY* HAZARDS REQUIRING VISUAL DETECTION SLIGHT HIGH Normal** Activity Level Low High Low High Illuminance Levels (Footcandles) 0.5 1 2 5 * Minimum illuminance for safety of people, absolute minimum at any time and at any location on any plane where safety is related to seeing condiions. ** Special conditions may require different illuminance levels. In some cases higher levels may be required, as for example where security is a factor. In some cases greatly reduced levels, including total darkness, may be necessary, specifi cally in situations involving manufacturing, handling, use, or processing of light-sensitive materials (notably in connection with photographic products). In these situations alternate methods of insuring safe operations should be relied upon. NOTE: See specific application reports of the IES for guidelines to minimum illuminances for safety by area. d. Precleaning. It is necessary for parts to be inspected to be free from dirt, contamination, or anything which would tend to obscure detection of important defects. It is also important during cleaning not to remove or obscure evidence of a defect. For example, cracks may become hidden by abrasive treatment and rendered invisible. e. Working Environment Factors. Excessive temperature,wind, rain, and other climactic factors tend to adversely affect inspections. Excessive noise tends to reduce concentration, cre ate tension, and prevent effective communication. These condi tions increase the likelihood of errors, degrade reliability, and potentially impact personnel safety. The FAA's human factors re- Chap 1 Page 18 Par 6 8/14/97 AC 43-204 search program addresses ~any factors which affect the reliabil ity of visual inspection. 7. SAFETY. a. General Safety. Safety hazards which could cause injury to the inspector or prevent the identification of defects should be eliminated or minimized. b. Safety Instructions for Inspection Systems and Materials. The operating safety instructions of the manufacturers of the in spection systems and materials should be followed. The eye can be harmed by intense lighting and lasers (which have their own associated safety regulations and precautions) . The various ma terials used for cleaning in preparation for visual inspection may contain chemicals which, if improperly used, can be hazardous to the health and safety of operators. Safe handling of cleaning materials is governed by the suppliers' Material Safety Data Sheets (MSDSs). MSDSs, conforming to 29 CFR 1910.1200, or equivalent, should be provided by the supplier to any user and should be prepared in accordance with FED-STD-313. Flammable or combustible cleaners and chemicals should be kept in approved safety containers and only in minimum quantities. Some cleaners and chemicals may have an adverse effect on skin, eyes, and res piratory tract. Manufacturers' warning labels and current safety directives should be observed. Cleaners and chemicals should be used only in authorized areas. Soiled flammable or combustible cloths should be discarded into covered metal containers. 8. THE VISUAL INSPECTION PROCESS. The process of visual inspec tion should contain two fundamental elements to be successful: (1) a trained inspector with binocular vision and good visual acuity; (2) an inspection procedure which defines the details of the inspection, including examples of the defect(s) tracked. This document presents examples of these elements and their in terrelation in aircraft inspection. The findings of qualified inspectors using appropriate procedures on specific details of an aircraft can be analyzed to provide quantitative data on the re liability of inspection for a given detail. Knowledge gained from this analysis establishes the time intervals at which the inspections are performed. a. Procedures and Processes for Visual Inspection. The various components of a modern aircraft vary depending upon their use, material makeup, method of fabrication, and the environment in which they operate. While most of the aids for the inspection 2 Office of Aviation Medicine Reports: Human Factors Issues in Maintenance and Inspection, 1994. Chap 1 Par 6 Page 19 AC 43-204 8/14/97 process are used for engines, airframes, related systems, compo nents, and accessories, they are used to a differing degree and may be modified and configured for specific applications. The major difference between inspection of engines and airframes is that only cursory inspections of engines can be made on the air craft. Although borescopes and other enhancements are expanding the number and quality of ~nspections on mounted engines, com plete and rigorous engine inspections necessitate their removal from the aircraft and, in many cases, full teardown. b. Generalized Techniques. Successful visual inspections on any type of structure usually embody known techniques and proce dures which have been developed by experience. Examples of such techniques are described in Section 9. c. Specific Techniques. There are specific techniques for detecting defects unique to airframes and engines. Specific guidelines and techniques used for inspection of airframes and engines are described in Sections 10 and 11, respectively. 9. VISUAL INSPECTION, GENERAL. To conduct an effective visual observation, inspection personnel should not only look at an ob ject, but examine it based on their knowledge of it and estab lished rules. a. Targets. Effective inspectors look at specific targets rather than scan an area. The eye is functionally blind when it is moving between observation points. Accordingly, a procedure of step-scanning is used. Lookouts spotting objects on the hori zon are taught to step scan with binoculars. Those who are pro ficient can detect approaching objects long before they are oth erwise visible. Similarly, when observing dim objects against a or dark background, observers are taught to focus to one side above the object viewed. They are then able to see details which are not otherwise visible. These and other types of methods can be used by inspectors to look for target defects in all parts of the aircraft. b. Imagination. Another useful technique for the inspector is to imagine what type of action would cause a particular de fect. This thought process may provide a clue as to what the de fect will look like. Skin wrinkles/ which may be caused by an underlying crack, are an example of a defect identified by such a process. c. Markinqs. Markings or anomalous concentrations of dis coloration may signal the presence of a defect. When smoking was permitted on aircraft, inspectors knew that nicotine smears were associated with skin cracks. Close inspection is still necessary where concentrations of contaminants and discoloration occur, since they may signal the existence of crack sites. Scratches, marks, and other anomalous features on the area inspected inform Chap Par 8 Page 20 l 8/14/97 AC 43-204 t trained inspector and are used to detect defects which may af airworthiness. Loose s tend to t "smoke", discol oration, and streaking (localized) . d. Corrosion. Corrosion is primarily detected by visual in spection. Since its detection is critical, inspection personnel should be 1 with the appearance of the common types of corrosion and have training and experience in corrosion detection on aircraft structural and engine materials. Corrosion Control Aircraft (AC 43-4A) contains technical information on corro sion identification, photos illustrating examples of typical cor rosion, and guidance on treatment of corrosion on aircraft struc tural, engine, and related materials. It may be necessary to re move corrosion to assess the condition of the underlying mate rial. It is important not to destroy the surface finish, or re move protective coatings which would be difficult to replace, such as the "cladding" found on the skin surface of major trans ports. In general aviation, an inspector will sometimes probe a part with a center punch in an area of suspected corrosion; if more than a minor indentation is observed, corrosion is present. e. Inspection After Maintenance. After a component has been serviced, repaired, or otherwise maintained, it should be in spected for abnormalities. A similar inspection of the surround ings should be carried out when a component or accessory is rein stalled in the aircraft. Look for loose material, missing coat ings, other damage, etc. 10. AIRFRAME VISUAL INSPECTION. It is necessary not only to know how to examine, but where to examine, when inspecting details for defects with which one is familiar from past inspections. The flashlight and the mirror are standard tools which should accom pany the inspector on all inspections. The inspector should be come skillful in using these tools. Also, magnifiers should be readily at hand for some types of inspections. Other aids which may be available for specialized requirements are described in Chapters 3 and 4. The flashlight/mirror combination can be used to illuminate an area as well as view it and is particularly valuable in inaccessible spots. Magnifiers are invaluable for defining the extent and character of cracks and problems in riv eted assemblies. a. Visual Detection of Surface Cracks. When searching for surface cracks with a flashlight, the light should be directed at a 5- to 45-degree angle (see Figure 1-18). The light beam should not be directed at such an angle that the reflected light beam shines directly into the eyes. The eyes should be focused above the beam during the inspection. The extent of any cracks can be determined by directing the light beam at right angles to the crack and tracing its length. A 10-power magnifying glass should be used to confirm the existence of a suspected crack. If this Chap 1 Par 9 Page 21 8/1 /9 AC 43-204 is not adequate, NDI techniques-such as particle, or eddy current-may be used to verify cracks. EYE ABOVE REFLECTED LIGHT BEAM CRACK OPEN TO SURFACE FIGURE 1-18. USING A FLASHLIGHT TO INSPECT FOR SURFACE CRACKS b. Visual Detection of Hidden Defects. The mirror can be used with great effect in locations that cannot be viewed di rectly. The mirror is frequently attached to a long arm so that it can be directed around corners. It is frequently necessary to shine a light onto the mirror and indirectly illuminate the area requiring or undergoing inspection. c. Hardware and Fasteners. Rivets, bolts, and other miscel laneous structural hardware should be inspected for looseness, integrity, proper size and fit, and corrosion. Dished, cracked, or missing rivet heads and loose rivets should be identified and recorded, using the arsenal of visual inspection techniques available. The inspector should ensure that sufficient light is available to be able to really see every fastener. Once again, a flashlight is indispensable. d. Control Systems. Cables, control rods, rod ends, fair leads, pulleys, and all other similar items should be examined for integrity, structural soundness, and corrosion. e. Visual Inspection for Corrosion. Inspection of an air craft for corrosion follows a systematic pattern. (1) Clues. The aircraft is initially observed for clues as to the care with which it has been maintained. Have obvious Chap Page 22 Par 10 l 8/14/97 AC 43-204 corrosion control measures been taken? · Have drains been cleaned, aced, debris removed? (2) Locations. Inspect likely corrosion sites. These include galleys and food service areas, lavatories, bilges, tank drains, and fastenings. When debris is found, it should be exam ined for iron oxide and the characteristically white powdery alu minum hydride. Biological contamination (mold, algae), which may feel greasy or slippery, frequently causes corrosion since it al ters the acidity of any moisture it contains. Caulking and seal ing compounds should be tested for sound adhesion since corrosion can rude under such materials. Nutplates should be investi gated for underlying corrosion. Tap tests should be performed frequently and any dull sounding areas investigated carefully. The use of a center punch or awl to indent a surface should be used with care, since awl or center punch pricks can serve as sites for the initiation of fatigue cracks. The omission of fuel additives by some fuel vendors can accelerate the deterioration of tankage on small aircraft. In such cases, it is necessary to drain tanks and inspect them using lighted borescopes or other aids. Flight and control surfaces are difficult to inspect since access is difficult. Extensive use of aids is recommended for such locations. (3) Sites. Careful detailed examination of corrosion sites is then accomplished to define the extent of corrosion. This can lead to removal of skin panels or other measures to fur ther define the extent of damage. f. Disbonds. Many aircraft have extensive regions of adhe sive bonding of the structure alone or in combination with riv ets. It is frequently necessary to detect disbonds and adhesive ilure in structure. It should be remembered that, in adhe sively bonded structures, evidence of corrosion frequently sig nals the loss of bond integrity. A good example of this condi tion is the pillowing which appears behind rivets. If the struc ture is bonded as well as riveted, one can be sure that where pillowing exists the bond is destroyed. Unfortunately, the re verse is not also true. It is quite possible for an uncorroded joint to be disbanded. Frequently, the only means for detecting such a disbond is to mechanically distort the structure and de termine whether any adhesion exists in the area of interest. Specifically, the waffle doublers, which act as tear preventers in pressurized aircraft, should be tested where possible. g. Painted Surfaces. Painted surfaces should be inspected for chipped, missing, loose or blistered paint and for evidence of corrosion. Refer to AC 43-4A for examples of corrosion. h. Windshields and Ports. Transparent surfaces-such as windshields, windows, and ports-should be inspected for cracks, crazing, and seeds using a Larascope or similar device. This de- Chap 1 Par 10 Page 23 AC 43-204 8/14/97 vice uses a plastic prism to permit viewing the interior of transparent plastic or glass window material. The prism is opti cally coupled to the window being inspected by use of an oil couplant, enabling the operator to see inside the glass. The prism can be manipulated to observe if any cracks are emanating from drill holes or from edges of the transparent material. i. Other Surface Discontinuities. Other surface disconti nuities-such as discoloration from overheating; buckled, bulging, or dented skin; cracked, chafed, split, or dented tubing; chafed electrical wiring; delaminations of composites; and damaged pro tective finishes-may be found by careful visual inspection. 11. ENGINE VISUAL INSPECTION. Some superficial clues to engine condition are leaks and evidence of smoke. Details observed in engine inspection which differ from airframe inspection generally relate to surface finish and the means for inferring underlying conditions. a. Forgings, Weldments. Castings, and Machined Parts. The surface texture of the components differs from that of the rolled and formed surfaces most common in airframes. The components are therefore inspected using different criteria. So many engine de fects are related to surface features of the material that a glossary of terms is used in most engine manuals to describe visible surface characteristics in terms of the process which caused them and its effect on satisfactory performance of the part. As a result, much of the current guidance relating to en gine visual inspection is related to manufacturing processes. This document covers only those visual inspection issues relating to operational and maintenance inspection. The Engine Visual In spection Glossary in this document, however, describes defects which may be found by maintenance inspectors in the field, but are more often found in the manufacturing process rather than "in-service" operations or maintenance. b. Engine Environment. Another difference related to engine inspection is associated with the environment in which engines are expected to operate. Many engine parts are expected to sur vive in intense heat. Inspections within the protective enclo sures surrounding these areas often require complex visual aids such as light pipes, borescopes, and special inspection fixtur ing. 12. INSPECTION FOR SPECIFIC TYPES OF CORROSION. This section provides general information for visual inspection of aircraft structure and components for specific types of corrosion. Visual inspection is the primary method for inspecting aircraft struc ture and components for corrosion. Other NDI techniques such as eddy current, ultrasonic, radiographic, magnetic particle, and penetrant inspection are also used to supplement visual inspec tion. These other NDI techniques are generally used when costly Chap 1 Par 10 Page 24 8/14/97 AC 43-204 disassembly would be required to gain access to hidden structureor components to accomplish visual inspections. They are also used to measure or estimate material loss due to corrosion and to verify the effectiveness of corrosion removal. Inspection of aircraft for corrosion is a continuing requirement and should be done on a daily basis. a. Corrosion. Corrosion is the electrochemical deteriora tion of a metal because of its reaction with the surrounding en vironment. While new and better materials are continuously being developed, this progress is offset, in part, by a more aggressive operational environment. Corrosion is a complex phenomenon which can take many different forms and the resistance of aircraft ma terials to corrosion can drastically change with only a small en vironmental change. b. Catastrophic Corrosion Events. Corrosion is most often thought of as a slow process of material deterioration, taking place over a significant period of time (examples being general corrosion, pitting, exfoliation, etc.). Other forms of corrosiondegradation can occur very quickly, in days or even hours, with catastrophic results. These forms (such as stress corrosioncracking, environmental embrittlement, and corrosion fatigue) depend on both the chemical and mechanical aspects of the environ ment and can cause catastrophic structural failure without warn ing. c. Corrosion Occurrence. Corrosion occurs on almost all metals; however, the use of corrosion resistant metals and the application of protective coatings minimize aircraft corrosion. Many other factors contribute to the amount and degree of aircraft corrosion such as the operational environment, materials used in the original design, and the amount of operational pres ervation provided during maintenance and repair. d. Aircraft Environment. Aircraft exposed to salt air, heavy industrial pollution, and/or over water operations will ex perience more corrosion problems than aircraft operated in a dryenvironment. Corrosion is caused by the presence of salts in moist air or by some other abatement to corrosion present in thechemical content of the water or elements in the metal. e. Manufacturers' Handbooks. Manufacturers' handbooks should be used as a general guide when an area is to be inspected for corrosion. Some manufacturers have developed videos explaining the process of corrosion and separate corrosion control manu als that are the basis for a complete aircraft corrosion inspec tion and program. On aircraft for which the manufacturer has not published a recommended corrosion inspection schedule and treat ment program, the recommendations of Advisory Circular (AC) 43-4A, Corrosion Control for Aircraft, should be followed. Chap 1 Par 12 Page 25 AC 43-204 8 / 14/ 97 f. Uniform Etch Corrosion. Uniform etch corrosion results from a relatively uniform chemical attack on a metal surface (see Figure 1 - 19). On a polished surface, this type of corrosion is first seen as a general dulling of the surface, and if the attack is allowed to continue, the surface becomes rough and possibly frosted in appearance. FIGURE 1-19. UNIFORM ETCH CORROSION (Courtesy of Thomas Flournoy) Page 26 Chap 1 Par 12 8/14/97 3 20 most common on tt It as FIGURE 1-20. PITTING CORROSION h. dis simi electrolyte ries lists follows. 1.2. 3.4. 5 . 6 . 7. 8. 9 . 10. 11. Bronze 12.13. 14. 15.16. Silver 17. 18. 19. 20. 21. s te s * 2024 tionsbeen corrosion. Chap 1 Par 12 27 8/14/97 AC 43-204 • FIGURE 1-21. GALVANIC CORROSION OF MAGNESIUM ADJACENT TO STEEL FASTENER (Courtesy of Thomas Flournoy) Chap 1 Page 28 Par 12 8/14/97 AC 43-204 The rate and degree of corrosion depends on the relative surfaceareas of the two metals and their location on the electromotive force series. Adjacent metals in the EMF series have low corro sion susceptibility whereas widely separated metals will corrode rapidly. For example, an aluminum fastener in contact with a relatively inert Monel (nickel, copper, steel) structure may cor rode severely, while a Monel bracket secured to a large aluminum member would result in a relatively superficial attack on the aluminum sheet. i. Concentration Cell or Crevice Corrosion. Concentration cell corrosion is corrosion of metals in a metal-to-metal joint; corrosion at the edge of a joint, even through joined metals are identical; or corrosion of a spot on the metal surface covered by a foreign material (see Figure 1-22 for the three types of crev ice corrosion) . LOW METAL ION CONCENTRATION HIGH METAL ION CONCENTRATION LOW OXYGEN CONCENTRATION METAL 101'-: CONCENTRATION CELL OXYGEN CONCENTRATIOI-! CEL~ RIVETED LAP JOINT PASSIVE FILM-----. PROTECTS EXPOSED SURFACE ACTIVE METAL ACTIVE- PASSIVE CELL FIGURE 1-22. CONCENTRATION CELL CORROSION j. Intergranular Corrosion. Intergranular corrosion is an attack along the grain boundaries of a material. Rapid selectivecorrosion at the grain boundary can occur with subsequent delami nation (see Figure 1-23). High-strength aluminum alloys such as 2014 and 7075 are more susceptible to intergranular corrosion if they have been improperly heat-treated and are then exposed to a corrosive environment. Chap 1 Par 12 Page 29 A~ 43-204 8/14/97 FIGURE 1-23. INTERGRANULAR CRACKING AND CORROSION ON A WINGSPAR CHORD k. Exfoliation Corrosion. Exfoliation corrosion is an ad vanced form of intergranular corrosion where the surface grains of a metal are lifted up by the force of expanding corrosionproducts occurring at the grain boundaries just below the su r face. The lifting up or swelling is visible evidence of exfoliation corrosion (see Figure 1-24). Exfoliation is most prone to occur in rolled and wrought products such as extrusions, thicksheet, thin plate, and certain die-forged shapes. This is in contrast with cast products that tend to have a more homogen eous grain structure. Chap 1 Page 30 Par 12 B/14/97 A'J 43 · 204 ' 0 FIGURE 1-24. SEVERE EXFOLIATION CORROSION {Courtesy of Thomas Flournoy) 13.-199. RESERVED. Chap 1 Par 12 Pages 31 through 42 AC 43-204 8/14/97 CHAPTER 2. VISUAL INSPECTION PROCEDURES 200. GENERAL. Generally, inspection procedure to be used will be specif by the rcraft or component manufacturers or the FAA in documents such as maintenance or overhaul manuals, AD's, SSID's, or manufacturers' Service Bulletins. If, during on the aircraft being inspected maintenance, a condition is found which may recur on that aircraft or on another of its type, a certified inspector or other appropriate individual should create inspection procedure covering the condition. Approval of an procedures should be accordance with appropriate FARs. 201. MATERIAL CONTAINED IN A VISUAL INSPECTION PROCEDURE. Visual inspection procedures should l contain steps in a logical for mat. A procedure has four basic parts: (1) a basis for the in spection, (2) preparatory arrangements, (3) implementation of the inspection, and (4) evaluation of the ts. Table 2-1 is a listing of all the elements to be considered when creating or re viewing an inspection procedure. Each of the items in the Table should be addressed the procedure if relevant for the specific inspection. Chap 2 Page 43 Par 200 J.~c 3-2 8/14/97 TABLE 2-1. PREPARING OR PROCEDLJRE BASIS FOR INSPECTION Reason for and purpose of the any relevant background infor mation. References to documentation, for Airwor thiness Directives, Manufacturers and general other relevant manuals. Controlling dates: Effective date date before which the in should be accomplished, date at which the inspection no longer is necessary. Effectiveness; aircraft, , or part number. Time and labor required for the inspection. Conditions under which the necessary. PREPARATION surface preparation over which the is effective. Identification of any equipment necessary for the together with provisions for periodic calibration thereof. Identification of the materials approved for the inspection. These may be included in a referenced Qualified Products List. IMPLEMENTATION Description of the defect to be detected, preferably with an illustration of a sample defect. Postcleaning instructions if required. Instructions for disposition of the article if it cannot be returned to service. EVALUATION Procedure for establishing Accept/reject criteria. requirements. Some act ties fically calledout in they are relevant. Chap Page 44 Par 201 2 8/14/97 AC 43-204 a. Preliminary Inspection. A preliminary inspection of the overall general area should be performed for cleanliness, pres ence of foreign objects, deformed or missing fasteners, security of parts/ corrosion/ and damage. If the configuration or loca tion of the part conceals the area to be inspected, it is appro priate to use visual aids such as mirror or borescope. b. Precleaning. The areas or surface of parts to be in spected should be cleaned without damaging any surface treatment which may be present. Contaminants that might hinder the discov ery of existing surface indications should be removed. Some cleaning methods may remove indications of damage; care should be used if the cleaning tends to smear or hide possible indications of trouble. Surface coatings may have to be removed at a later time if other NDI techniques are required to verify any indica tions that are found. Some typical cleaning materials and meth ods used to prepare parts for visual inspection are detergent cleaners, alkaline cleaners, vapor degreasing, solvent cleaners, mechanical cleaning, paint removers, steam cleaning, and ultra sonic cleaning. c. Corrosion Treatment. Any corrosion found in the prelimi nary inspection should be removed before starting a close visualinspection of any selected part or area. Manufacturers' hand books, when available, are a good general guide for treatment of corrosion. Recommendations of AC 43-4A, if appropriate, should be used on aircraft for which the manufacturer has not published a recommended corrosion inspection schedule or treatment program. The AC contains a summary of current 1 data regarding identification and treatment of corrosion on aircraft structure and engine materials. Examples of types of corrosion damage de tectable by the visual method are also given. d. Use of Visual Aids. When inspecting the area required, visual aids should be used as necessary. An inspector normally should have available suitable measuring devices: a flashlight and a mirror. Chapter 3 provides information on lighting techniques that can be used when inspecting for defects in different types of materials. 203. RECORD KEEPING. All defects found should be documented by Maintenance Record entry, written report, squawk sheet, photo graph, or video recording for appropriate evaluation. Depending on the rules governing the facility and person performing the inspection, the report may be limited to simply reporting findingswithout any rejection or acceptance disposition. The type, loca tion, and approximate size of any defects present should be docu mented. Based upon the particular inspection process specifica tion (i.e., AD, Service Bulletin, Maintenance Manual requirement, or normal inspection discovery) the mechanic, repairman, or other authorized person should determine the particular acceptance, re- Chap 2 Par 202 Page 45 AC 43-204 8/14/97 work, repair or rejection status of the part or structure being inspected. a. Findings. One of the most important elements of the vis ual inspection process is the nature of the report of findings. As a guide, the record of findings for any defects should be kept in a manner as to permit others who may be doing the same inspec tion to have the benefit of any previous information found and experience gained. b. Maintenance of Records. The full value of visual inspec tion can be realized only if records are kept of the conditions found on parts inspected. The size and shape of the finding and its location should be recorded along with other pertinent infor mation/ such as rework performed or disposition. The inclusion of some permanent record of a defect on a report makes the report much more complete. c. Illustrations as Records. It should be stressed that frequent and effective use of illustrations not only will enhance the effectiveness of the procedure but is indispensable in commu nicating to the inspector the nature of the defects to be found. In addition to textual and anecdotal data, the following types of records are commonly used: (1) Sketches. The simplest record is a sketch of the part showing the location and extent of the defect. On large ar eas it may be sufficient to sketch only the critical area. (2) Photography. Photographs (still or video recording) of defects can be taken for visual record purposes. Photographs produce a permanent and highly descriptive record since they show both size and location on the part. They are permanent/ repro ducible, and the required equipment is readily available. It is good practice to include a scale in the photo when practicable as well as some marking for identification. This is particularly necessary if the photograph is likely to become an exhibit in volved in litigation. Chap Page 46 Par 203 2 8/14/97 AC 43-204 204. FOUR LEVELS OF VISUAL INSPECTION. a. Inspection Tasks. Visual inspection tasks are divided into four categories relating to their difficulty and degree of effectiveness as follows: • Walkaround Inspection. • General Visual Inspection. • Detailed Visual Inspection. • Special Detailed Visual Inspection. b. Additional Special NDI. An additional category may be used when visual inspection is supplemented by special ized NDI equipment. 205. ACCEPTABLE PRACTICE FOR VISUAL INSPECTION. Acceptable prac tice for the four levels of visual inspection is defined in the following paragraphs. For each level, the practice is divided into the four parts of the inspection procedure described in Ta ble 2-1. Details of the inspection procedures will vary for dif ferent types of operators and aircraft; for example, the walk around for a general aviation aircraft and a commercial jet will have major differences. It is important however, that the proce dure for each aircraft type in a given service be carried out with the same care and detail every time the aircraft is in spected. Also, in all inspections described herein, the inspec tor should have available and be familiar with the documentation and reporting forms and the ground rules mandating the inspec tion. Refer to Appendices A through F for sample visual inspec tion procedures and equipment. a. Level 1. Walkaround. The walkaround inspection is a general check conducted from ground level to detect discrepancies and to determine general condition and security. NOTE: This is the only one of the four inspections that may be accomplished by either flight or maintenance personnel. The focus and perspective will varybased on the relation of the inspection to flight or maintenance operations. (1) Basis for Inspection. Most maintenance instructions mandate walkaround inspections on a periodic basis. The overall purpose is to serve as a quick check to determine if detectable inconsistencies exist which would affect the performance of the aircraft. Chap 2 Par 204 Page 47 AC 43-204 8/14/97 (2) Preparation for the Inspection. Aircraft history be to gain information use in ing craft (e.g., are there recurring problems or have there been hard landings?). In addition the aircraft should be clean enough for an effective inspection to take place, the necessary tools and equipment should be available (e.g., flashlight, rag, notebook), and other aids tools, and procedures may be necessary (e.g., in 1 spection of some aircraft is easier if already on jacks, but this is not always necessary) . (3) Implementation. Beginning the inspection at the nose, the inspector should approach the inspection from the per spective of the pilot and mechanic by, first, determining general condition and, second, identifying maintenance items. A good rule is to check for items affecting safety, legality, effi ciency, and comfort. The following paragraphs give a partial listing of things to look for. Each aircraft will be different, but a surprising number of different aircraft have similar struc tural details. ® Observe left and right side of fuselage and left and right wings. (Does the aircraft list?) Work to your left. Check general condition of paint. Check exterior surface components within reach. Check windows. Check engine, propellers or fan blades, exhaust area, and pylons. Check leading edges everywhere. Check control surfaces for slop, wear, and security. Check each gear well. Check all entry and exit points to the aircraft. Check static dischargers. Observe surfaces at different angles using available light to enhance surface evaluation. @ Examine according to what the standard condition is. (Question the existence of any unusual condi tion.) Look for anything different from one side to another. (It is important to shake, push, pull, listen, and feel when possible.) Run your hand over skin junction areas or composite surfaces. ® Walk around twice. (Observations during the first cursory walkaround the aircraft should be used to determine the general condition. On the second time around revisit the areas noted on the initial walk and look for other discrepancies that may be revealed through closer scrutiny of a specific area. This is when specific locations should be observed.) Chap 2 Page 48 Par 205 8/14/97 AC 43-204 • Are there major dents or intrusions in the skin? Look for evidence of flexing parts, waves in the skin, weave or bubble in fiber glass or composite components, eroded fairings, and bulging or flat tened seals. Are any external components bent? Is there evidence of damage? Check windows for craz ing, dirt, and pitting. • Rivet characteristics should be noted. Observe rivets for damage. Look for loose broken or miss ing rivets. Localized chipping of paint cracked 1 paint on sealant, or fretting corrosion are indica tive of movement. Look for smoked or stained riv ets. • Check all venting for leaks. Check all input tub ing to insure it is clear. Check all antennas for chipping and strikes. Check for obstructions in pitot tubes, static and engine pressure orifices/ and temperature venturies. (4) Findings. Init findings should be recorded in a personal notebook as soon as discrepancies are discovered. Do not rely on memory. Findings should be transferred to the air craft log or official record of discrepancy as soon as possible. Recommendations for action will depend on whether the inspection precedes flight operations or maintenance and whether the dis crepancy is safety or flight ical. b. Level 2. General. A general inspection is made of an ex terior with selected hatches and openings open or an interiorr when called for, to detect damage/ failure 1 or irregularity. (1) Basis for Inspection. When a specific problem is suspected, the general inspection is carried out to identifyr if possible, the difficulty. General inspections are also routinely used when panels are open for normal maintenance. (2) Preparation for the Inspection. Ensure cleanliness of the aircraft. The necessary tools and equipment required may include flashlight, mirror, notebook, droplight, rolling stool, tools for removal of panels, ladders standsr or platforms. Other aids such as jacking of the aircraft may or may not be discre tionary; knowledge of a specific aircraft may be essential; and common problems may require information, even if not on the in spection card. (3) Implementation. General looking is not enough. As the inspector, you should continually ask "What is wrong with this picture?" Be inquisitive. Question whether you have seen Chap 2 Page 49 Par 205 AC 43-204 8/14/97 this before. Move, shake, pull, twist, and push all parts possi ble. Apply weight to load bearing components. Compare one side to the other if applicable. Be aware of other systems in the in spection area. Look for abnormalities in the area, even if not related to this inspection. Adjusting the source of illumina tion, view items under inspection from different angles. Is the area pressurized? If so, does this affect any part of the in spection? Inspect all structural components, all moveable parts, all attach points, and brackets. Check all cables, conduits, and hoses for condition and clearance. Check condition and security of load and stress points. Look for chafing and fretting corro sion. Observe proximity of one part to another. Look for loose or missing fasteners, use of proper sealants, noticeable cracks, indications of corrosion, and debris in closed areas. Observe that cables, conduits, and hoses are properly routed. Observe that there is sufficient strain relief. Observe rivets for darn age. Look for smoked rivets and discoloration of paint. (Localized chipping of paint, cracked paint on sealant, or fret ting corrosion are indicative of movement.) (4) Findings. Transfer all information relating to dis crepancies from your notebook. Record discrepancies as a work order. Discoveries during the inspection may indicate the need for a more detailed inspection. Depending on the findings, this may be either a Level 3 or Level 4. c. Level 3. Detailed. A detailed visual inspection is an intensive visual examination of a specific area, system, or as sembly to detect damage failure or irregularity. Available in spection aids should be used. Surface preparation and elaborate access procedures may be required. (1) Basis for Inspection. A detailed inspection is called for when a specific problem is suspected and the general inspection dictates additional inspection. Or, if the inspection is otherwise mandated, a detailed visual inspection is carried out to identify, if possible, the difficulty. Detailed inspec tions are also periodically called for on damage-tolerant air craft to ensure the airworthiness of the critical structure. (2) Preparation for the Inspection. Tools and equipment will vary, but may include a prism, supplemental lighting, mir ror, magnifying glass, flashlight, dye penetrant, notebook, drop light, rolling stool, and standard and specialized hand tools. Documentation required is specific to the procedures outlined by steps on work cards. Also review the SBs, ADs, aircraft history, and accident reports. Other aids such as knowledge of a specific aircraft and common problems may be essential even if not on the inspection card. (3) Implementation. The reasoning that originally dic tated the inspection should be considered. If it was because Chap 2 Page 50 Par 205 8/14/97 AC 43-204 some corrosion was found, then a more in-depth examination is re quired. If the inspection is in response to an AD for a crack, carefully inspect the surrounding area to rule out additional oc currences or stress induced because of the crack. In a detailed inspection, you are usually searching for failure, damage, or ir regularity. Check the condition and security of lockwires and the load and stress points. Look for fretting corrosion. Ob serve proximity of one part to another. Look for loose or miss ing fasteners, use of proper sealants/ obvious cracks, indica tions of corrosion, and debris in closed areas. Observe that ca bles, conduits/ and hoses are properly routed. Observe that there is sufficient strain relief. Look to see if any chafing has occurred. (4) Findinos. Recommendations (discoveries during this inspection may indicate the need for a more detailed inspection, such as a Level 4). d. Level 4. Special Detailed. A special detailed inspec tion is an intensive examination of a specific item, installa tion, or assembly to detect damage, failure, or irregularity. It is likely to make use of specialized techniques and equipment. Intricate disassembly and cleaning may be required. (1) Basis for Inspection. As systems and structures have become more complex, special inspections using extraordinary techniques and equipment have evolved to ensure airworthiness. These are covered in instructions for special detailed inspec tions. Special detailed inspections are also periodically called for on damage-tolerant aircraft to ensure the airworthiness of the critical structure. This level of inspection may also be in voked based on recommendations from a lower level. (2) Preparation for the Inspection. Tools and equipment will vary but may include a flashlight, mirror, video borescopes, special aids and tooling, Dremel, rolling stool, image enhance ment and recording devices, supplemental lighting, magnifying glass, dye penetrant, notebook, and standard and specialized hand tools. Documentation required is specific to the procedures out lined by steps on work cards; review of SBsr ADs, and aircraft history; and reference to the original or referred discrepancy, if any. Another aid is the discrepancy report from the contract ing NDI company. (3) Implementation. Procedures are defined in detail by the specific instruction procedure, but they are limited to the scope of visual inspection. The locations to be inspected will vary greatly, but may include portions of the aircraft that are inaccessible without major disassembly, such as the interior sur face of the wing skin, pylon butt joints, and lap joints. In some of these cases the objective of the inspection may be best Chap 2 Par 205 Page 51 AC 43-204 8/14/97 served both practically and economically through the use of NDI techniques. (4) Findings. Satisfy documentation that specified this level of inspection. Documentation will be both internal and ex ternal and may include work cards, ADs and SBs. Recommendations should include recommendations for correction of the discre~ancy and follow-up inspection. 206.-299. RESERVED. Chap 2 Pages 52 through 62 Par 205 8/14/97 43-204 CR~PTER 3. VISUAL INSPECTION AIDS 300. GENERAL. sual inspection are illuminat types. Illumination and lighting are cruc sual inspection and can vastly feet In the following sec tions these two process will be dis cussed. In s of lighting in the inspection In the section cover ing visual aids, have found utility in rcraft inspect a. eye-mirror an ion for visual inspection. flashlight is Aircraft structure and components ring inspection are fre quently located beneath skin, , control rods, pumps, and actuators. good secondary access by re flection is often essent Vi inspection aids usually con sist of a strong fl ight, a mirror with a ball joint, and a 2 to 5-power simple magnif The rror should be of adequate size (except for very access situations) with reflecting surface free of , , and worn coating; and the swivel joint should be tight enough to its setting. A magnify ing mirror may be useful in some situations. A 10-power magni fier is recommended for pos identification of suspected cracks; however, NDI techniques, such as dye penetrant, magnetic partie , or eddy current can also be used to verify in dications. Visual inspection of some areas can only be accom pli use of remote devices, such as borescopes and video imaging systems. b. sual inspection is a ubiquitous process many locat and involves numerous special techniques. Each will an opt lighting environment and its own types of visual and optical enhancements. It is up to the inspector to select the appropriate illumination and optical aid for the inspection at hand. 301. LIGHTING AND ILLUMINA~ION. Federal Aviation Regulation, Section 145.35(g) dealing with il s requires that lighting should be adequate for work be performed and should not adversely affect the quality of the work. Such lighting can be provided by a combination of general background and supplemental th ice and be task dependent. illumination and will vary The amount of light the variety of seeing tasks in visual inspection and re components depends not only on itself, but so on the vision and the age of the worker (vision may need correcting with glasses and older Chap 3 Page 63 Par 300 AC 43-204 8/14/97 eyes require more light), the importance of t (how criti cal or expensive is a mistake), reflectance task background (the greater the dif between task and background, the easier it is to see) a. General Considerations for Lighting Aircraft Maintenance Areas. The following factors should be considered as 1 important requirements of good planning for aircraft maintenance lighting systems: (1) Safetv of Personnel. Determine the quantity, qual ity, and type of illumination desirable for safety of personnel, the maintenance processes, and the environment. (2) Selection of Lighting Equipment. Select lighting equipment that will provide the quantity and quality requirements by examining luminance characteristics and performance that will meet installation, operating, and actual maintenance conditions. (3) Equipment Maintenance. Select and arrange lighting equipment so that it will be easy and practical to maintain. (4) Energy Management. Energy management considerations and economic factors, including initial operating and maintenance costs versus the quantity and quality requirements for optimum visual performance, should be balanced (reference IES handbooks on lighting, also see Appendix G in this document). Whenever possible, the use of daylight should be considered for mainte nance areas. Due consideration should be given to the National Energy Policy Act of 1992 covering the use of energy efficient illumination. b. Illuminance Values. The IES has provided a range of il luminance values and illuminance categories to be used for ge neric types of interior activities when specific recommendations are not available (see Table 3-1). Chap 3 Page 64 Par 30~ 8/14/97 AC 43-204 TABLE 3-1. ILLUMINa~CE VALUES ILLUMINANCE CATEGORIES AND ILLUMINANCE VALUES FOR GENERIC TYPES OF ACTIVITIES RANGE OF ILLUMINANCE ILLUMINANCES REFERENCE TYPE OF ACTIVITY CATEGORY (FOOTCANDLES) WORK-PLANE Public spaces with A 2-3-5 dark surroundings Simple orientation B 5-7.5-10 General for short temporary lighting visits throughout spaces Working spaces c 10-15-20 where visual tasks are only occasion ally performed Performance of vis- D 20-30-50 ual tasks of high contrast or small size Performance of vis- E 50-75-100 Illuminance ual tasks of medium on task contrast or small size Performance of vis- F 100-150-200 ual tasks of low contrast or very small size Performance of vis- G 200-300-500 ual tasks of low contrast or very small size over a prolonged period Performance of very H 500-750-1000 Illumination prolonged and ex- of task ob- acting visual task tained by a combination of general and local (supplementa ry lighting) Performance of very I 1000-1500-200 special visual tasks of extremely low contrast and small size The IES has also established a procedure (range approach) for se lecting illuminance values from the ranges listed in Table 3-1 by Chap 3 Par 301 Page 65 AC 43-204 8/14/97 using a weighting-factor reflecting lighting- t {see Table 3-2). It was es t ished to accommodate a need for flexibility in determining illuminances so that lighting designers could design lighting systems to meet specific needs. Such flexibility requires that additional information be available to effectively use the range approach. To use the range approach, a lighting task should be considered to be composed of the following elements: TABLE 3-2. WEIGHTING FACTORS TO BE CONSIDERED IN SELECTING SPECIFIC ILLUMINANCE WITHIN RANGES OF VALUES FOR EACH ILLUMINANCE CATEGORY a. For Illuminance Categories A through c Room and Occupant Characteristics Weighting Factor -1 0 +1 Occupants' ages Under 40 40-55 Over 55 Room surface re- Greater than 30 to 70 Less than 30 flectances* 70 percent percent percent b. For Illuminance Categories D through I Task and Worker Characteristics Weighting Factor -1 0 +1 Workers' ages Under 40 40-55 Over 55 Speed and/or accu- Not Important Important Critical racy** Reflectance of Greater than 30 to 70 Less than 30 task background*** 70 percent percent percent * Average weighted surface reflectances including wall, floor and ceiling reflectances if they encompass a large portion of the task area or visual surroundings. For instance in an aircraft hanger where the ceiling height is 25 neither the task nor feet, the visual surroundings encompass the ceiling, so only the floor and wall reflectances would be con sidered. In determining whether speed and/or accuracy is not important, important, or critical, the following questions need to be answered: What are the time limitations? Will errors produce an unsafe condition or product? Will errors reduce productivity and be costly? For example, in reading for leisure there are no time limitations and it is not important to read rapidly. Errors will not be costly and will not be related to safety. Thus, speed and/or accuracy is not important. If, however, safety notes and process procedures are to be read by NDI personnel, accuracy is critical because errors could produce an unsafe con dition, and speed is important for econowic re2sons. The task background is that portion of the task against which the meaningful visual display is exhibited. For example, on this page the meaningful visual display includes each letter which combines with other letters to form words and phrases. The display me d~um, or task background, s the paper, which ~as a reflectance of approximately 85 per- ce:Jt. Chap 3 Page 66 Par 301 3/:4/37 ~ 43-224 ( l ' I~ I (i) Visual Disclay. visual display is t ject being viewed, which is presumed to present some inherent ob- difficulty of observation. (ii) Observer Age. The age of the observer is a factor in the observer's visual performance. (iii) Speed and/or Accuracy. The importance of speed and/or accuracy distinguishes between casual, important, and critical seeing requirements. (iv) Task Reflectance. The reflectance of the task (background against which the details are seen) . The reflectance will determine the type of illumination best adapted to the re flectance characteristics of the visual display. (2) Amount and Type of Light. The above lighting task elements should be considered concurrently to determine the ap propriate amount and type of light for the lighting task. Addi tional information on using this range approacr procedure for se lecting illuminances is provided by the IES in its handbooks on lighting, and in Appendix G of this document. c. Industrial Lighting. In addition to generic-activity lighting recommendations, the IES through technical committeesand knowledgeable individuals provides lighting recommendations for specific industries. Table 3-3 provides the IES recommended illuminance categories for general industrial inspection area/activity. The IES standards contain lighting recommenda tions for specific tasks and areas in aircraft maintenance. TABLE 3-3. IES RECOMMENDED ILLUMINANCE CATEGORIES FOR THE DESIGN AND EVALUATION OF LIGHTING SYSTEMS FOR INDUSTRIAL INSPECTION AREAS INDUSTRIAL GROUP (*Inspection Area/Activity Only) Area/Activity Illuminance Category** Inspection Simple D Moderately Difficult E Difficult F Very Difficult G Exacting H The IES provides a wide variety of ind~strial area/activity recommendations for illumi nance categories in the Industrial Group. See Tab.;,e 3-1. Chap 3 Par 301 Page 67 AC 43-20 8/14/97 d. The s tasks for vi spection ft tend to be three dimensional and curved, rather than two dimensional and flat like seeing tasks found an office. The seeing can almost any distance from the floor, compared with 30 inches for the typical desk top, and in any position from horizontal to vertical. The seeing task can have extremely fine detail requiring thousands of footcandles or be so large that s will suffice. The finish of the article to inspected (dull or matte versus shiny or mirror 1 versus brushed) great affects the amount and orientation of the lighting needed for good sibility. Good vi t 1 depends not only on providing the right illumination levels, but also on selecting the proper lamp and luminaire and mounting or positioning it in the right loca tion. In fact, the ter can often have far more effect on task visibility than the lighting level. Figures 3-1, through 3-3 show examples of the effects of article finish and lighting ori entation on visibility. The shiny and matte finish micrometers, shown in Figure 3-1, typify a range of seeing tasks and the ef fect of lighting system orientation. The graduations on the bar rel of the matte finish micrometer are highly legible under all three lighting conditions: fluorescent parallel to the barrel (Figure 3-1A), fluorescent perpendicular to the barrel (Figure 3 1B), and high-intensity discharge (HID) downlight (Figure 3-1C). A B c FIGURE 3-1. EXAMPLE OF THE EFFECT OF SHINY AND MATTE FINISH OF PARTS AND LIGHTING SYSTEM ORIENTATION ON SEEING TASKS (Courtesy of General Electric Company) The graduations of the shiny micrometer cannot be easily read when the barrel is parallel to the fluorescent lighting (Figure 3-lA) because of lines of glare. When the lighting is perpen dicular (Figure 3-lB), the reflections wrap around the surface, Chap 3 Page 68 Par 301 8/14/97 AC 43-204 contrast is improved ly, and the graduations are easily legible. The downlight system (Figure 3-1C) tends to be omnidirectional and the legibility of the numbers is intermediate between parallel and perpendicular fluorescent lighting. The solder connections on the circuit board, shown in Figure 3-2, are difficult to inspect because of the reflections of the bright HID downlight (Figure 3-2A). Under the large, low-brightness fluorescent luminaire (Figure 3-2B), the reflections are soft and diffuse and defects can be easily detected. A B FIGURE 3-2. EXAMPLE OF THE EFFECT OF LIGHTING SYSTEMS INSPECTION OF A CIRCUIT BOARD (Courtesy of General Electric Company) ON Scribe marks, shown in Figure 3-3, (and many defects) on polished or lightly etched surfaces are more visible if they are parallel to the fluorescent lighting (Figure 3-3A) rather than at right angles to it (Figure 3-3B), since the surface reflects the darker area between the fixtures and increases the contrast. Chap 3 Par 301 Page 69 AC 43-204 8/1 /97 A B FIGURE 3-3. EXAMPLE OF THE EFFECT OF LIGHTING SYSTEM ORIENTATION ON AN INSPECTION SURFACE (Courtesy of General Electric Company) e. Visual tasks number, but some can be classified according to common characteristics. The detail to be seen in each group can be emphasized by an application of certain lighting fundamentals. Table 3-4 classifies tasks according to their physical and light-controlling sties and suggests lighting techniques for good visual perception. Chap 3 Page 70 Par 301 8/14/97 AC 43-204 TABLE 3-4. CLASSIFICATION OF VISUAL TASKS AND SUPPLEMENTARY LIGHTING TECHNIQUES (Sheet 1 of 3) PART I FLAT SURFACES CLASSIFICATION OF VISUAL TASK EXAMPLE SUPPLEMENTARY LIGHTTNG TECHNIQUE General Lighting Lumi:J.aire Characteristics Description I Requirements Type* Locate Luminaire A. Opaque Materials l. Diffuse detail and background Unbroken surface Reading ADs Hi.gh visibility S-III or S-II To prevent direct or SBs with comfort glare and shadows Broken surface Scratch or To emphasize sur- S-I To direct light crack on face break obliquely to the anodized surface aluminum 2. Mirror finish detail and background Unbroken surface Dent, warps, Emphasize uneven- s-v So that image of uneven sur- ness source and pattern face in skin is reflected to panels eyeBroken surface Scratch, Create contrast of S-III or So detail appears scribe, en- cut against mirror bright against a graving, finish surface dark background punch marks, cracks S-IV or s-v So that image of when not prac- source is re tical to ori- fleeted to eye and ent task break appears dark Mirror finish coating Inspection To show up uncov- S-IV with For reflection of over mirror finish of finish ered areas color source source image to- background plating over selected to ward the eye underplating create maximum color contrast between two coatings 3. Combined mirror finish and diffuse surfaces Mirror finish detail on Shiny i.nk on To produce maximum S-III or S-IV So direction of diffuse, light back- anodized contrast without reflected light ground aluminum veiling ref lee- does not coincide tions with angle of view Mirror finish detail on Punch or To create bright S-II or S-III So direction of diffuse, dark back- scribe marks reflection from reflected light ground on dull detail from detail coin- metal cide with angle of view Diffuse detail on mir- Graduation To create a uni- S-IV or S-III So direction of ror finish, light back- on a steel form, low bright- reflected light ground scale ness reflection does not coincide from mirrored with angle of view background Diffuse detail on mir- Wax marks on To produce high S-III or S-II So direction of ror finish, dark back- aircraft brightness of de- reflected light ground painted sur- tail against dark does not coincideface background with angle of view B. Translucent Materials 1. With diffuse sur- Frosted or Maximum visibility Treat as opaque, diffuse surface face etched glass of surface detail (see A-1 I or plastic, Maximum visibility Transilluminate behind material with light weight of detail within S-II, S-III, or S-IV fabrics material 2. With diffuse sur- Scratch on Maximum visibility Transilluminate behind material with face opal glass of detail within S-II, S-III, or s-rv or plastic material Maximum visibility Treat as opaque, mirror finish sur of surface detail face - See A-2 Chap 3 Par 301 Page 71 AC 43-204 8/14/97 TABLE 3 4. CLASSIFICATION OF VISUAL TASKS AND SUPPLEMENTaRY LIGHTING TECHNIQUES (Sheet 2 of 3) PART I FLAT SURFACES (Continued) CLASSIFICATION OF VISUAL TASK EXAMPLE SUPPLEMENTARY General Lighting Lumina ire Type* I Characteristics Description Requirements c. Transparent Materials Clear material with Plate glass To produce visi- s-v and S-I mirror finish surface bility of details within material such as bubbles, and details on surface such as scratches D. Transparent over Opaque Materials 1. Transparent mate- Instrument Maximum visibility S-I rial over a diffuse panel of scale and background pointer without veiling reflections Varnished Maximum visibility s-v wing spar of detail on or in the transparentcoating or on the diffuse background emphasis of uneven surface 2. Transparent mate- Glass mirror Maximum visibility S-I rial over a mirror fin- of detail on or in ish background transparent mate rial Maximum visibility s-v of detail on mir ror finish back ground PART II THREE DIMENSIONAL OBJECTS CLASSIFICATION OF VISUAL TASK EXAMPLE SUPPLEMENTARY General Lighting Luminaire Characteristics Description Requirements Type* A. Opaque Materials 1. Diffuse detail and Dirt on a To emphasize de- S-III or S-II background casting or tail with a poor or blow holes contrast in a casting S-I or S-III or S-II as a black light source when object has a fluo rescent coat ing LIGHTING TECHNIQUE Locate Lumina ire Transparent mate rial should move in front of Type s-v, then in front of black back ground with Type S-I directed obliquely. Type S-I should be di rected to prevent glare So reflection of source does not coincide with an gle of view So that image of source and pattern is reflected to the eye So reflection of source does not coincide with an gle of view. Mir ror should reflect a black background So that image of source and pattern is reflected to the eye LIGHTING TECHNIQUE Locate Luminaire To prevent direct glare and shadows In relation to task to emphasize detail by means of high light and shadow To direct ultravio let radiation to all points to be checked Chap 3 Par 30~ Page 72 8/14/97 AC 43-204 TABLE 3-4. CLASSIFICATION OF VISUAL TASKS AND SUPPLEMENTARY LIGHTING TECHNIQUES (Sheet 3 of 3) PART II THREE DIMENSIONAL OBJECTS CLASSIFICATION OF VISUAL TASK EXAMPLE General Lighting Characteristics Description Requirements 2. Mirror finish detail and background a. Detail on the sur- Dent in pol- To emphasize sur face ished alumi- face unevenness num skin Inspection To show up areas of finish not properly plating over plated underplating b. Detail in the sur- Scratch or To emphasize sur face crack on face break polished aluminum skin 3. Combination mirror finish and diffuse a. Mirror finish de- Scribe mark To make line glit tail on diffuse back- on casting ter against dull ground background b. Diffuse detail on Micrometer To create luminous mirror finish back- scale background against ground which scale mark ings can be seen in high contrast B. Translucent Materials 1. Diffuse surface Interior To show imperfec lighting tions in material diffusers 2. Mirror finish sur- Glass en- To emphasize sur face closing face irregulari globe, ties frosted lens cover To check homogene ity c. Transparent Materials Clear material with Windshields To emphasize sur mirror finish surface face irregulari ties To emphasize cracks, chips, and foreign particles (Continued) SUPPLEMENTARY Lumina ire Type* s-v s-IV plus proper color S-IV S-III or S-II s-IV or S-II s-rr s-v s-:tr s-I s-IV or s-v LIGHTING TECHNIQUE Locat<! Lumina ire To reflect image ofsource eye To reflect image of source to eye To reflect image of source to eye In relation to taskfor best visibility. Adjustable equipment often helpful. Overhead to reflect image of source to eye With axis normal of micrometer Behind or within for transillumination Overhead to reflect image of source to eye Behind or within for transillumination To be directed obliquely to objects Behind for transil lumination. Motion of objects helpful f. Quality of Illumination. Quality of illumination per tains to the distribution of luminances in the visual environment. The term is used in a positive sense and implies that all luminances contribute favorably to visual performance! visualcomfort, ease of seeing, safety, and esthetics for the specific visual task involved. Glare, diffusion, direction, uniformity, color, luminance, and luminance ratios all have a significant ef fect on visibility and the ability to see easily, accurately, and quickly. Certain industrial seeing tasks, such as visual inspec tion, require discernment of fine details and need much more careful analysis and higher quality illumination than others. Chap 3 Par 301 Page 73 43-204 8/14/97 Whenever possible! the quality of illumination for the particular visual ion task being performed should be , includ ing the use of test parts with discontinuities of the type being sought. Areas where the seeing tasks are severe and performed over long periods of time require much higher quality than where seeing tasks are casual or of relatively short duration. Indus trial lighting installations of very poor qua~ity are easily rec ognized as uncomfortable and are possibly hazardous. Unfortu nately, moderate lighting deficiencies are not readily detected, although the cumulative effect of even slightly glaring condi tions can result in substantial loss of seeing efficiency and un due fatigue. (1) Glare, General. Glare is unwanted light in the field of view which causes loss in visual performance and visi bility. It occurs when luminances within the visual field are substantially greater than the amount of luminance to which the eyes are adapted. It can be caused by a source of light (direct glare) or can be reflected from any surface in the room including the task (reflected glare) . (2) Direct Glare. Direct glare is often the result of the luminaire not shielding the lamp from view (see Figures 3-4A and 3-4B). It may be noticeably severe with lamps of high lumi nance values. For example, a clear 250-watt, high-pressure so dium lamp that emits 27r500 lumens from a cigarette-size arc tube will be much brighter than a 400-watt, metal-halide lamp emitting 36,000 lumens from a melon-size, phosphor-coated lamp envelope. Portions of some mirrored reflectors can reflect an overly bright image of the lamp (see Figure 3-4C) . Lens-enclosed luminaires may eliminate bare-lamp brightness, but can themselves cause di rect glare at certain angles. Fluorescent luminaires with their 1 relatively low-brightness lamps/ usually will be less glaring. Avoiding direct glare is simply a matter of choosing the right luminaire and its location. (3) Reflected Glare (Veiling Reflection). Reflected glare is somewhat more insidious than direct glare. Images of the lamps or the luminaires are reflected from the viewing task (see Figure 3-4D). These veiling reflections can be severe enough to cause errors during visual inspection. The following suggestions are provided for avoiding reflected glare: • Change the position of the viewing task and/or the offending luminaire(s) 1 if practicable. This will change the angular relationship between the light source/ task and observer/ thereby directing the 1 offending reflection elsewhere. • Use a dull or matte finish, not a shiny one, on surfaces surrounding the task such as the machin ery/ toolsr benches/ wallsr etc. Chap 3 Page 74 Par 30l 8/14/97 AC 43 204 • Replace clear lamps with diffuse-coated ones. A B C D FIGURE 3-4. EXAMPLES OF DIRECT AND REFLECTED GLARE (Courtesy of General Electric Company) e Change the lighting system, if required. For example, replace HID downlight luminaires with those that have large-area lenses (large surfaces will be less bright and reduce reflections) or with fluorescent. • Use a large-area fluorescent lighting system. The reflections will be uniform and low in luminance. A translucent panel system is often recommended for inspecting mirrored metal and plastic articlesfor surface defects. Chap 3 Par 301 Page 75 AC 43-204 8/14/97 ~ Use specialized supplementary lighting where glare problem is limited to a locations. the g. control Luminaire Shielding. The purpose or direct the light from the lamp. of a luminaire is to This is accomplished by the size/ shape, and material of the reflector and auxiliary devices such as baffles, louvers, lenses, and diffusers. For industrial lighting applications, including inspection areas, shielding should be at least 25 degrees and preferably approach ing 45 degrees (see Figure 3-5), especially in areas of high il lumination levels or with high-brightness lamps. Fluorescent fixtures might also require crosswise baffles or louvers if in spection personnel view the lamps lengthwise. At low mounting heights/ well-shielded, narrow-beam luminaires, particularly HID, may produce puddles of light at the viewing task level. If wider beamspread and better uniformity is obtained by reducing shield ing, the visible bare lamp becomes glaring. The following recom mendations are provided for avoiding this problem: (1) Low Mounting Heights. Install HID luminaires that have been designed for low mounting heights. These have large diameter reflectors and refractors that provide the widespread beam. Because the light from the lamp is spread over the refrac tor's much larger areas, it in effect becomes the light source. Therefore, the brightness is diluted and reduced to tolerable levels. Brightness will vary with the lamp's output and the size of the refractor. (2) Narrow-Beam Luminaires. Use more of the same nar row-beam luminaires, but with lower-wattage lamps and closer spacing. Properly selected, there will be both acceptable over lap and reduced direct glare. Fluorescent lamps, even though they are inherently lower in brightness than HID lamps, should have deep reflectors and lateral baffles. Chap 3 Par 301 Page 76 8/14/97 AC 43-204 FIGURE 3-5. EXAMPLE OF LUMINAIRE SHIELDING ANGLE (Courtesy of General Electric Company} h. Uniformity of Illumination. Uniformity refers to the variations in illumination levels that occur at the work plane, typically with the highest level under the luminaire and the low est in between luminaires. The IES considers illuminance to be uniform if the maximum level is not more than one-sixth above the average leveli or the minimum, one-sixth below. Uniform horizon tal illumination is called for in most lighting designs where seeing tasks require the same levels. Closer spaced luminaires improve uniformity and ensure continued illumination in the event one or two luminaires are temporarily extinguished. Using IES recommended reflectances (see Table 3-5} helps improve uniformity and helps reduce unwanted shadows. Ceilings should be painted a flat white to reduce contrast between fixture and ceiling and to increase illumination. The key to satisfactory uniform lighting is to observe the fixture manufacturer's recommended maximum spacing-to-mounting-height ratio or a similar guide, the spacing criterion. Chap 3 Par 301 Page 77 AC 43 204 8/14/97 TABLE 3-5. RECOMMENDED REFLECT&~CE VALUES FOR INDUSTRIAL LIGHTING REFLECTANCE* SURFACES (Percent) Ceiling 80 to 90 Walls 40 to 60 Desk and bench tops, and equipment machines 25 to 45 Floors not less than 20 Reflectance should be maintained as near as practical to recommended values. (1) Maintaininq Uniformitv. Maintaining uniformity of illumination between adjacent areas which have significantly dif ferent visibility and illumination requirements might be wasteful of energyi for example, a storage area adjacent to a machine shop. In such instances, it is prudent to design and apply non uniform lighting between those areas. It may be accomplished by using luminaires of different wattage and/or by adjusting the number of luminaires per unit area. Local lighting restricted to a small work area is unsatisfactory unless there is sufficient general illumination. (2) Harsh Shadows. Harsh shadows should be avoided, but some shadow effect may be desirable to accentuate the depth and form of objects. There are a few specific visual tasks where clearly defined shadows improve visibility and such effects should be provided by supplementary lighting equipment arranged for the particular task. Figures 3-6 and 3-7 illustrate how shadows can aid or hinder the seeing of details. In the case of curved and faceted surfaces which are polished or semipolished, the direction of the lighting is important in controlling high lights. Some shadow contributes to the identification of form. Chap 3 Page 78 Par 30l 8/14/97 3-204 FIGURE 3-6. HARSH SHADOWS PRODUCED BY UNIDIRECTIONAL ILLUMINATION (Left) AND SOFT SHADOWS PRODUCED BY DIFFUSE ILLUMINATION Chap 3 Par 301 Page 79 8/14/97 AC 43-204 FIGURE 3-7. MULTIPLE SHADOWS (Upper Left) ARE CONFUSING; SINGLE SHADOWS (Center) MAY CONFUSE, BUT CAN HELP; DIFFUSED LIGHT (Lower Right) ERASES THE SHADOWS (3) Briohtness. Brightness is the strength of sensa tion which results from viewing surfaces or spaces from which light comes to the eye. This sensation is determined in part by luminance (which can be measured) and in part by conditions of observation, such as the state of adaptation of the eye. The eye responds to differences in brightness or contrast. Improving the the goal of the lighting designer. contrast of the seeing task is However, extreme variations in brightness in the surrounding field of view can make seeing more difficult or even uncomfort able. The eye becomes tired when the pupil has to adjust con stantly from light to dark and back again. As recommended by the IES, the ratio of the luminance of the seeing task to the sur rounding areas for comfortable seeing is shown in Table 3-6. Chap 3 Par 301 Page 80 8/14/97 AC 43-204 TABLE 3-6. RECOMMENDED MAXIMUM LU