8/14/97 AC 43-204 complished with a specially designed borescope and working chan- A rotary file or stone is connected to a drive cable that passes through the working channel and a drive motor connected to this cable rotates the cutter/stone, with speed controlled by a variable-rate foot pedal. The technician operates the tool to blend damaged blades while viewing the work process on a video monitor. A video micrometer is also incorporated into the system to allow measurements to be taken.
FIGURE 4-26. POWER BLENDING BORESCOPE KIT (Courtesy of Machida, Inc.)
(6) ShadowProbe™. The ShadowProbe™ measuring fiberscope system measures cracks, defects, and small objects while conducting remote inspections (see Figure 4-27). The Shadow- Probe™ system is designed to make measurements without comparison to reference objects by casting a shadow pattern across the system image, which is used by a system on-board computer to de- Chap 4 Par 404 Page 153
termine magnification, distance, object size and dimensions. Operators manipulate a cursor on a video screen to locate the shadow and objects to be measured. The video screen is electronically corrected for lens distortion and has built-in automatic calibration for magnification from near or far away, over a full 85-degree viewing field.
there is keyboard access to three different measurement modes to allow measurement of linear distance, depth, or objects at skewed angles.
TREM BIRDANCE
LEN OF CATE REACHER PARLAN FIGURE 4-27. SHADOWPROBE™ MEASURING SYSTEM (Courtesy of Welch Allyn, Inc.)
g. Borescope Selection Questions. By answering the following questions and reviewing the information in this document and borescope manufacturers' literature, a prospective borescope user can determine which borescope offers advantages over another for Chap 4 Page 154 Par 404
8/14/97 AU 43-204 a specific inspection. The answers to these questions can also be used as a guide for selecting or purchasing the most effective borescope for a particular application.
(1) Access Opening Inside Diameter (i.d.). How wide is the borescope entry point and what is the smallest i.d. that the borescope should pass through?
(2) Travel Path Geometry. Is the travel path geometry straight or curved? If a guide tube is required, what is the most severe bend the guide tube should negotiate and what is the
i.d. at this point?
(3) Guide lube. is a guide tube needed to racilitate borescope insertion? Is it offered with the borescope? Will it have to be custom manufactured or formed on site?
Borescope Length. What is the minimum length needed to travel to reach the inspection site? Is additional length needed for protection of the eyepiece or safety of the inspector using the borescope? Is a drawing available to study and lay out the access path requirements? The length of the borescope insercion probe should be well thought out, since it is related to costs and a longer insertion tube can be difficult to control ir an inspection with a shallow travel path. In many circumstances, two separate borescopes for different inspections will be more economical than using one scope for multiple purposes. The probability of damage and cost of repair increases with increased borescope working length.
Target Inspection Area Location. Where is the target inspection area in relation to the distal tip when the borescope reaches the target? If a flexible borescope is being considered, is there room in the work piece channel for articulating the bending section to face the target inspection area directly? How far from the target inspection area will the borescope tip be during the inspection? will variable magnification and direction of view tip adapters be required now or later?
(6) Resolution. What is the smallest dimension needed to be seen? Can the defect be large or are microscopic defects also harmful? What will happen if a microscopic defect is missed?
Frequency of Borescope Use. How often will the borescope be used? How long will the borescope be used for each inspection? How many inspections will be made for each use?
many people will use the borescope?
Chap 4 Par 404 Page 155
Documentation. Will photo or video documentation of the inspection/defect be needed?
(9) Verification of Borescope Specifications. Can the borescopes specifications be verified independent of the supplier?
(10) Borescope Operation. Is an operating manual provided with the borescope that is adequate for the user's needs?
Is training available to improve inspection results and reduce wear and tear on borescopes?
405. LIST OF EQUIPMENT USED IN VISUAL INSPECTION. Appendix G provides a partial listing of equipment useful in accomplishing visual inspections.
406.-499. RESERVED.
Chap 4 Pages 156 through 166 Par 404
CHAPTER 5. DEFINITIONS
500. DEFINITIONS.
AC Advisory Circular AD Airworthiness Directive CRE Code of Federal Regulations CIE International Commission on Illumination MF Electromotive Force PAA Federal Aviation Administration FAR Federal Aviation Regulation HID High-Intensity discharge (type of illumination) IES Illumination Engineering Society Kelvin MSDS - Material Safety Data Sheets NFPA - National Fire Protection Association NDI - Nondestructive Inspection NDT - Nondestructive Testing SB - Service Bulletin SSID - Supplementary Structural Inspection Document UL - Underwriters' Laboratories, Inc.
ACTIVE: Referring to the negative direction of electrode potential (opposite of noble).
ANEROBIC: An absence of oxygen in the uncombined state.
ANGSTROM (A): Unit of length usually reserved for the expression ot wavelength. One angstrom equals 10 centimeter (cm). Under the standard system of units, the angstrom will be replaced by the nanometer (nm) (1.0 A = 0.10 nm). The angstrom is the standard unit for measuring wavelength of light.
ANODE: An electrode at which oxidation of the anode surface or some component of the solution is occurring (opposite of cathode) .
BRIGHTNESS: The strength of sensation 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.
BuLB: A source oi electrically powered light. This term is used to distinquish between an assembled unit consisting of a light source in a housing called a "lamp" and the internal source. See LAMP.
CANDELA (cd): The metric unit of luminous intensity. One candela is one lumen per steradian (formally candle).
Chap 5 Par 500 Page 167
AC 43 - 204 8/14/97 CATHODE: The electrode of an electrolytic cell at which reduction occurs (opposite of anode).
CELL: An electrochemical system consisting of a cathode and anode immersed in an electrolyte. The anode and cathode may be separate metals or dissimilar areas on the same metal.
CHARGE-COUPLED DEVICE (CCD): A microchip imaging sensor containing thousands of light-sensitive elements (pixels) arranged in a pattern of rows and columns. The CCD converts light from an image to electrons which, after processing, can be displayed as a picture on a video monitor.
CIE: International Commission on Illumination CLEAN: Free of contaminants.
CONCENTRATION CELL: A cell in which potential differences at the anode and cathode are the result of differences in chemistry (concentration of reactants or products) of the environment adjacent to the electrode.
CONTAMINANTS: Any material or material residue which interferes with the visual inspection process.
CORROSION: An electrochemical deterioration of a material, usually a metal, because of a reaction with its environment. (See AC 43-4A) .
CORROSION FATIGUE: A yielding of a metal resulting from the combined action of corrosion and fatigue (cyclic stressing).
CRAZING: Network of minute cracks appearing in the surface of a material.
CREVICE CORROSION: A localized corrosive attack resulting from the formation of a concentration cell in a crevice between two metal surfaces of a metal and nonmetal surface.
DEFECT: A discontinuity or group of discontinuities which do not meet specified acceptance criteria. One can have a defect within acceptable limits.
DEPOSIT: A foreign substance, which comes from the environment, adhering to a surface of a material.
DIRECT GLARE: Glare resulting from high luminances or insufficiently shielded light sources in the field of view. It is usually associated with bright areas, such as luminaires, ceilings and windows which are outside the visual task or region being viewed.
Chap 5 Page 168 Par 500
DISBOND: Areas where adhesive bonding no longer meets designed strength requirements.
DISCONTINUITY: An interruption in the normal physical structure or configuration of a part such as a crack, lap joint disbond, seam, inclusion, area of corrosion, or porosity. See DEFECT.
DUST-PROOF LUMINAIRE: A luminaire so constructed or protected that dust will not interfere with its successful operation.
DUST-TIGHT LUMINAIRE: A luminaire so constructed that dust will not enter the enclosing case.
ELECTRODE: An electrical conductor in contact with an electrolyte which serves as an electron acceptor or donor (see anode and cathode as specific examples).
ELECTROLYTE: A chemical substance or mixture, usually liquid, containing ions which migrate in an electric field.
ELECTROMOTIVE FORCE SERIES: A list of elements according to their standard electrode potentials with the value for hydrogen arbitrarily taken as 0.0 volt (also called Emf series).
EMBRITTLEMENT: A loss of load carrying capacity of a metal or alloy.
ENCLOSED AND GASKETED: See vapor-tight.
ENVIRONMENT: A description of the surroundings or conditions (physical, chemical, mechanical) in which a material exists.
EVALUATION: The review of discontinuities to determine if they meet specified acceptance criteria.
EXFOLIATION: A thick, layered growth of loose corrosion products often separating from the metal surface.
EXPLOSION-PROOF LUMINAIRE: A luminaire which is completely enclosed and capable of withstanding an explosion of a specific gas or vapor that may occur within it and preventing the ignition of flashes or explosion of the gas or vapor within. It must operate a specific gas or vapor surrounding the enclosure by sparks, nuch an exteal tampered cherray.
at such an external temperature that a surrounding flammable at- FAYING SURFACE: Interface between two adhesive surfaces.
FIELD OF VIEW: The angle in degrees that the entering light subtends at the exit pupil of the optical system. Also known as ANGLE OF FIELD.
Chap 5 Par 500 Page 169
FILIFORM CORROSION: A form of attack that occurs under films on metals and which appears as randomly distributed hairlines (also called Underfilm Corrosion).
FLAW: An imperfection in an item or material. Small flaws can be harmless. See DISCONTINUITY.
FOOTCANDLE: The unit of illuminance when the foot is taken as the unit of length.
square foot in area on which there is a uniformly distributed flux of one lumen or the illuminance produced on a surface all points of which are at a distance of one foot from a directionally uniform point source of one candela.
FRETTING CORROSION: A form of deterioration caused by repetitive friction between two sliding surfaces and accelerated by a common corrosive action.
GALVANIC CELL: A corrosion cell consisting of two dissimilar metals in contact or in a narrower context consisting of adjacent anodic and cathodic sites. The former definition is on a macroscale, the later on a micro-scale.
GALVANIC CORROSION: A type of corrosion associated with the current resulting from the coupling of dissimilar electrodes in an electrolyte.
GALVANIC SERIES: A listing of metals arranged according to their relative corrosion potentials in a specific environment (such as sea water) .
GENERAL CORROSION: A type of corrosion attack uniformly distributed over a metal surface (sometimes called uniform etch corrosion).
GRAIN BOUNDARY: A narrow zone in a metal corresponding to the transition from one crystallographic orientation to another, thus separating one grain from another. The atoms in each grain are arranged in an orderly pattern.
HEAT-AFFECTED ZONE: An area adjacent to a weld where heat has caused microstructural changes which affect the corrosion behavior of the metal.
HID: High Intensity Discharge (Type of illumination) HYDROGEN EMBRITTLEMENT: A reduction of the load carrying capability by entrance of hydrogen into the metal (e.g., during pickling or cathodic polarization).
HYDROGEN-STRESS CORROSION: A premature failure of a metal resulting from the combined action of tensile stresses and the penetration of hydrogen into the metal.
Chap 5 Page 170 Par 500
IES: Illumination Engineering Society ILLUMINANCE: The density of the luminous flux incident on a surface; it is the quotient of the luminous flux divided by the area of the surface when the latter is uniformly illuminated. Typical units are footcandles and lumens.
ILLUMINATE: To provide, cover, or fill with light.
LUMINANCE: The luminous flux from a point divided by the area upon which it falls. See IES Handbook. (Formerly PHOTOMETRIC BRIGHTNESS.)
LUMINANCE RATIO: The ratio of the luminances of any two areas in the visual field.
MARINE ENVIRONMENT: An environment immediately adjacent to the sea coast affected by prevailing winds, fog, and other factors.
METAL: In the context of this advisory circular, a metal, metallic alloy, or material or combinations of those which exhibit metal-like properties (are electrical conductors) and are subject to corrosive attack.
NANOMETER: A unit of length equal to one billionth of a meter, Or 10 meter. The nanometer has replaced the angstrom unit as a measurement of short wavelength, electromagnetic radiation.
NEWTON (N): The unit of force equal to 0.2232 lb.
NFPA: National Fire Protection Association NOBLE: Refers to the positive direction of electrode potential, thus resembling the noble metals (such as gold).
NONDESTRUCTIVE INSPECTION: Inspection to detect internal or concealed defects in materials using techniques that do not damage or destroy the items being inspected.
OBJECTIVE LENS: The optical lens nearest the object being viewed that receives the light from the object.
PASSIVE: A condition in which the behavior of a metal is more noble (less active) than its position in the Electromotive Force Series would predict. A surface film protects the underlying metal from corrosion (opposite of active).
PASSIVITY: A phenomenon by which an active metal becomes passive.
Chap 5 Par 500 Page 171
PITTING: A very localized type of corrosion attack resulting in deep penetration at only a few sites (opposite of general corrosion).
PHOTOMETRY: The measurement of quantities associated with light.
REFLECTANCE OF A SURFACE OR MEDIUM: The ratio of the reflected flux to the incident flux.
REFLECTED GLARE: Glare resulting from reflections of high luminances from polished or glossy surfaces in the field of view.
is usually associated with reflections from within a visual task or areas in close proximity to the region being viewed (see veiling reflections).
ROOM UTILIZATION FACTOR: The quotient of the luminous flux (lumens) received on the work-plane divided by that emitted by the luminaire.
RELATIVE HUMIDITY: A ratio (percentage) of the amount of moisture in the air compared to what it could hold if saturated at a given temperature.
RESIDUAL STRESS: A stress present in a metal that is free of external forces or temperature gradients, usually the result of fabrication processes, and can be tensile or compressive in na- RUSTING: A type of corrosion attack limited to ferrous materials which results in reddish-brown corrosion products.
SACRIFICIAL PROTECTION: A reduction or prevention of corrosion of metal by galvanically coupling it to a more anodic metal.
SCALING: • A formation at high temperature of thick corrosion product layers on a metal surface or the deposition of water insoluble constituents on a metal surface.
SEEDS: Small bubbles in glass introduced during the manufacturing process.
SMOKE, SMOKING: A haze of solid detritus (blackened aluminum compounds) caused by abrasion of a loose rivet and its surroundings.
STERADIAN (UNIT SOLID ANGLE): A solid angle subtending an area on the surface of a sphere equal to the square of the sphere radius.
Chap 5 Page 172 Par 500
STRESS-CORROSION CRACKING: A premature failure of a metal as the result of the combined action of tensile stresses and a corrosive environment. The surface tensile stresses may be residual or applied.
TARNISH: A surface discoloration of a metal caused by the formation of a thin film of corrosion product.
THRESHOLD STRESS: A limiting stress at which stress-corrosion or hydrogen-stress cracking will develop in a metal in a given exposure period.
VAPOR-TIGHT LUMINAIRE: A luminaire designed and approved for installation in damp or wet locations. It is also classified as "enclosed and gasketed."
VEILING REFLECTIONS: Regular reflections superimposed upon diffuse reflections from an object that partially or totally obscure the details to the seen by reducing the contrast (sometimes called reflected glare).
VISUAL TASK: The process of observing an object either with the aided or unaided eye and making an informed assessment of its condition.
WATTS (W): Time rate of transferring energy. Power equal to one joule per second. The following table is a conversion of light values to units of power.
Light Source* cd/in< kcd/m<
5.16 8 Clear sky Candle flame (sperm) 6.45 10 60-W inside frosted bulb 77.4 120 60-W "white bulb" 19.35 30 Fluorescent lamp, cool white, T-12 bulb, 5.3 8.2 medium loading High-intensity, mercury-arc type H33, 2.5 968 1,500 atm Clear glass neon tube, 15 mm, 60 mA 1.03 1.6 Source; "Marks Standard Handbook For Mechanical Engineers," 9th edition, E.A. Avallone, I.
Baumeister III, McGraw H1l1.
501 - 599. RESERVED.
Chap 5 Par 500 Pages 173 through 182