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.
Chap 1 Par 5 Page 11
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.
Chap 1 Page 12 Par 5
7-94223 7 24263 0:96930
NICK PICK-UP PILE-UF
PITTING SCORING SPALLING FIGURE 1-16. COMMON PHYSICAL CHARACTERISTICS OF ENGINE DEFECTS (Sheet 1 of 3) (Courtesy of Pratt & Whitney) Chap 1 Par 5 Page 13
• 63109
BLISTEP ING BRINELLING BURNING ₽ 61036 0 9420
BURNING CHIPPING CORROSION 9 85652 9-20%
CRACK CRACK AROSION FIGURE 1-16. COMMON PHYSICAL CHARACTERISTICS OF ENGINE DEFECTS (£ 70 2 7ЭЭЦ) Chap 1 Page 14 Par 5
FATIGUE PAILURE FLAKING FLOWING 9 94270 • 90262
FRACTURE FREETING CORROSION GARRITO 794205 9.94260 D7-4201
GOUGING GROOVEBIO GUTTERINO FIGURE 1-16. COMMON PHYSICAL CHARACTERISTICS OF ENGINE DEFECTS (Sheet 3 of 3) Page 15
TYPICAL SURFACE FINISHES
MACHINE FINISHES MANUFRCTURING BLEMISHES hing Done ou the Cutting Shor Mocks That Mop Our Dunc
TYPICAL CORROSION IMAGES
SAMPLE ENDOSCOPE IMAGES FIGURE 1-17. TYPICAL DEFECTS AS SEEN THROUGH BORESCOPE AND
OTHER AIDS (Courtesy of McDonnell Douglas) Chap 1 Page 16 Par 5
6. FACTORS AFFECTING VISUAL INSPECTION. Any factor that aids visual effectiveness increases the probability of detecting the potential cause of a failure and subsequent corrective action.
Inspection Personnel Qualifications and Training. Inspection personnel should posses experience and knowledge of the origins and causes of defects in raw material manufacturing processes, the reshaping and redistribution of these defects in subsequent part manufacturing processes, and defects that develop after the part is put in service. Inspection personnel should also have a working knowledge of the part, component, or aircraft being inspected. It is essential that inspection personnel be knowledgeable concerning the structural detail being evaluated to enable them to properly locate, identify, and evaluate aircraft defects. Persons who inspect, approve, and return to service an aircraft appliance or part, must be certified in accordance with the appropriate FARS or perform the work under a certificate holder who is directly in charge of that person.
Inspection Area Access. Ease of access to the inspection area is important in obtaining reliable visual inspection results. Access consists of the act of getting into an inspection position (primary access) and performing the visual inspection (secondary access). Unusual positions (i.e., crouching, lying on back, and overhead reaching) constitute examples of difficult ac- Impact on Inspection. The necessity to get both hands into the aircraft structure while holding a flashlight or mirror or reaching into awkward openings can affect the inspector's motivation, attitude, decision-making, and ability to interpret what is seen.
(2) Access and Safety. Staging equipment (e.g., forms, ladders, stools) used to permit access to the airframe and engines should be used safely, i.e., secured manually or brake engaged to prevent slips and falls. Protection should be provided to prevent potential injury from sharp edges and shifts in heavy weights. Adequate protection from falls should be provided wherever possible, such as railings and harnesses and lanyards on high working platforms.
c. Lighting. Adequate quality and intensity of illuminance and elimination of direct glare, reflected glare, and harsh shadows all enhance the identification of defects. Conversely, cessive visual fatigue and the delayed eye adaptation experienced when moving from bright surroundings into dark ones and vice versa could reduce effective detection of defects.
(1) Localized Illumination. Illumination should be provided during occupancy of spaces that possess limited access. In Chap 1 Par 6 Page 17
those areas which do not have fixed lighting, portable and vehicle-mounted lighting equipment should be used.
(2) Excessive Glare. Uncontrolled 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 carelessness could have been partially due to poor lighting. Illumination levels regarded as absolute minimums for safety alone have been developed by the IES and are listed in Table 1-1.
TABLE 1-1. ILLUMINANCE LEVELS FOR SAFETY*
HAZARDS REQUIRING VISUAL SLIGHT HIGH
DETECTION Normal** Activity Level LOW High LOW High Illuminance Levels 0.5 1 2 5 (Footcandles) 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, specifically 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, create tension, and prevent effective communication. These conditions increase the likelihood of errors, degrade reliability, and potentially impact personnel safety. The FAA's human factors re- Chap 1 Page 18 Par 6
search program addresses many factors which affect the reliability 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 inspection 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 materials 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 respiratory 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.
THE VISUAL INSPECTION PROCESS. The process of visual inspection 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 interrelation 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 reliability of inspection for a given detail. Knowledge gained from this analysis establishes the time intervals at which the inspections are performed.
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 Office of Aviation Medicine Reports: Human Factors Issues in Maintenance and Inspection, 1994.
Chap 1 Par 6 Page 19
process are used for engines, airframes, related systems, components, 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- Although borescopes and other enhancements are expanding the number and quality of inspections on mounted engines, complete 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 procedures which have been developed by experience. Examples of such techniques are described in Section 9.
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 object, but examine it based on their knowledge of it and established rules.
Targets. Effective inspectors look at specific targets rather than scan an area. The eye is functionally blind when it is moving between observation points. Accordingıy, a procedure of step-scanning is used. Lookouts spotting objects on the horizon are taught to step-scan with binoculars. Those who are proficient can detect approaching objects long before they are otherwise visible. Similarly, when observing dim objects against a dark background, observers are taught to focus to one side or 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.
is to imagine what type of action would cause a particular de- b. Imagination. Another useful technique for the inspector fect. This thought process may provide a clue as to what the defect 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. Markings. Markings or anomalous concentrations of discoloration 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 1 Page 20 Par 8