Appendix 3 Austenitic A term applied to that condition of iron associated with a change in crystal structure that makes it nonmagnetic. This occurs with ordinary iron at an elevated temperature. When sufficient chromium and nickel are present, lead becomes austenitic (nonmagnetic) at atmospheric temperatures. This is the case with many stainless steels that combine about 18% chromium and 8% or more nickel.
Bilge The lowest point of an aircraft’s inner hull. This is the area where cable runs, wire bundles, and coaxial cables are routed, and lights and antennas are often mounted.
Capillary Action The action by which the surface of a liquid in contact with a solid is advanced or retarded (raised or lowered). This is caused by the relative attraction of the liquid molecules to each other (surface tension) and those of the solid. The wicking of fluid up a cloth is an example of capillary action.
Carbonize To convert into carbon residue, usually by high heat.
Cathode The less-active electrode of a corrosion cell, where the action of the corrosion current causes a reduction reaction.
Cation A positively charged ion of an electrolyte which migrates toward the cathode. Metal ions, such as iron or copper, are cations.
Caustic Embrittlement The result of the combined action of tensile stress and corrosion in an alkaline solution. This can occur in riveted lap joints where there is a concentration of an alkali solution.
Cell In the corrosion process, a cell is a source of an electrical current that is responsible for the corrosion. It consists of an anode and a cathode immersed in an electrolyte and electrically joined together. The anode and cathode may be separate metals or dissimilar areas on the same metal.
Chemical Conversion Coating A chemical treatment of a metal surface, such as aluminum or magnesium, which results in a protective (corrosion resistant) film on the metal’s surface. The coating also greatly enhances paint adhesion.
Chloride A compound of chlorine. Many varieties of this compound are present in seawater and contribute to making the seawater an electrolyte (electrical conductive).
Clear Water Colorless water containing no visible suspended particles.
Appendix 3 Compound Substances containing two or more elements.
Concentration Cell An electrolytic cell, consisting of an electrolyte and two electrodes of the same metal or alloy, that develops a difference in potential as a result of a difference in concentration of ions (most often metal ions) or oxygen at different points in the solution.
Conformal Coating A closely adhering moisture and gas barrier applied to circuit boards to prevent corrosion and breakdown of electrical insulation.
Corona A faint glow adjacent to the surface of an electrical conductor at high voltage.
Corrosion The deterioration of a substance (usually a metal) because of a reaction with its environment.
Corrosion Fatigue A reduction in the ability of a metal to withstand cyclic stress by its exposure to a corrosive environment.
Corrosion Rate The speed or rate of a corrosion attack expressed in material weight loss per unit of time.
Couple Two or more metals or alloys in electrical contact with each other. These usually act as the electrodes of a cell if they are immersed in an electrolyte.
Critical Avionics Components Miniature or microminiature circuits including the components, printed circuit boards, tunable coils, tuned circuits, and devices with gold- or silver-plated connectors or contacts.
Critical Humidity The relative humidity, under a specific set of conditions, at which a metal or an alloy will begin to corrode. In the presence of hygroscopic (moisture-absorptive) solids or corrosion products, the critical humidity will be lowered. For example, steel will not corrode if the relative humidity is less than 30 percent in a marine atmosphere.
Deionized Water Water which has had various minerals and inorganic materials removed by means of an ion exchange process.
Desiccant A drying agent which acts by absorbing moisture.
Appendix 3 Distilled Water Water which has various organic and inorganic materials removed by means of an evaporation and condensation (distillation) process.
Durability Ability of avionics equipment or components to function and sustain stress in field service for a specific period of time with economical maintenance. The durability is measured in terms of minimum acceptable failure free lifetime (MFL) and expected maximum lifetime (EML), including repairs.
Elastomer A synthetic material with elastic properties.
Electrode A metal or alloy that is in contact with an electrolyte and serves as the site where electricity passes in either direction between the electrolyte and metal. The current in the electrode itself is a flow of electrons, whereas, in the electrolyte ions carry electrical charges, and it is their orderly movement in solution which constitutes a flow of current in the electrolyte.
Electrolyte Any substance which, in solution or fused, exists as electrically charged ions that render the liquid capable of conducting a current. Soluble acids, bases, and salts, such as those in seawater, are electrolytes.
Element Substances which cannot be decomposed by ordinary chemical changes or made by these changes.
Embrittlement Severe loss of ductility of a metal alloy.
Emulsified One liquid dispersed throughout another liquid with which it will not mix to form a homogeneous solution.
Encapsulant The general term describing materials used to envelop or fill a void to prevent the entrance of moisture or fungus. Conformal coatings, fungus-proof coatings, and potting compounds are all forms of encapsulants.
Ester/Diester Oils Oils containing synthetic materials known as esters or diesters, which are chemically formed by the reaction of an alcohol and an acid. These synthetic oils can attack certain plastics and paints.
Exfoliation The breaking away of a material from its surface in flakes or layers. A thick layer-like growth of corrosion products.
Appendix 3 Expected Maximum Lifetime The expected maximum period of time over which an avionics system, subsystem, module, or component performs satisfactorily. This includes acceptable availability, operation, and support cost (specific number of repair cycles).
Fatigue Tendency of a material to fracture in a brittle manner under repeated cyclic stressing or load at stress or load levels below its tensile strength.
Faying Surface The common surface between mating surfaces of parts.
Fungus A group of celled organisms (eukaryotic) that get their nutrients by secreting enzymes that break down organic matter in the tissue of other living or dead organisms. They then absorb the resulting nutrients. Includes mold, mildews, smut, mushrooms, and some bacteria.
Galvanic Couple Two electrically connected dissimilar metal conductors (may be a single metal in alloy) immersed in an electrolyte.
Galvanic Series A list of metals and metal alloys arranged in an order of their relative electrical potentials for a given environment. The order of their arrangement in one list may be different in another environment.
Hydrogen Embrittlement Loss of ductility of a metal caused by the entrance or absorption of hydrogen ions.
Hygroscopic The property of readily absorbing and retaining moisture.
Inorganic Coating A coating composed of matter other than of plant or mineral origin (i.e., electroplating, chemical conversion coating, anodize, phosphate, or oxide, etc.).
Ion An electrically charged atom or group of atoms. The sign of the charge is positive in the case of cations and negative in the case of anions.
Malfunction The improper operation of a component or system.
Microbes Microscopic living plants or organisms such as germs, molds, bacteria, and fungi.
Mil A unit of length equal to one thousandth of an inch (0.001 inch).
Appendix 3 Minimum Failure Free Lifetime (MFL) The minimum period of time that an avionics system, subsystem, module, or component performs satisfactorily without failure.
Nitrates Compounds including certain combinations of nitrogen and oxygen. Present in many industrial pollutants.
Noble Metal A metal usually found as uncombined metal in nature. Platinum, gold, and silver are noble metals.
Noncritical Avionics Components Components such as tube sockets, mechanical devices, knobs, and hardware.
Non-Destructive Inspection A method used to check the soundness of a material or a part without diminishing the strength, value, quality, or serviceability of the part.
Organic Coating A coating composed of matter derived from living organisms or carbon-based compounds
(i.e., paint, plastic, grease, preservative).
Outgassing Emission of a gas during the cure or decomposition of organic material. Usually increases with a rise in temperature.
Passivation The process or processes that cause a metal to become inert in a given corrosive environment.
pH A measure of hydrogen ions in concentration of a solution (pH 7 is neutral; below 7 is acidic;
above 7 is basic or alkaline).
Phantom Gripe An intermittent malfunction or failure which cannot be verified, identified, or duplicated for corrective action.
Pitting A form of corrosion that develops in highly localized areas of a metal surface that is not attacked elsewhere to any great extent. This corrosion attack results in the development of cavities or pits.
Pits may vary from deep cavities of small diameter to relatively shallow depressions.
Plasticizer A chemical added to rubber or resins to impart flexibility.
Appendix 3 Polyethylene A thermal plastic (softens when heated) characterized by its high impact strength, high electrical resistively, nontoxicity, and combustibility. One of several plastics used in wire coating.
Potting Compound A rubber-like material, usually poured, which cures to a hard consistency and provides moisture and vibration resistance to the item.
Primer Coat The first coat of a protective paint system. Improves adhesion of the succeeding topcoat and usually contains a corrosion inhibitor.
Reduction Reaction Gain of electrons by a constituent of a chemical reaction.
Relative Humidity The ratio of the amount of water vapor in the air at a specific temperature to the maximum amount that the air could hold at that temperature, expressed as a percentage.
Reversion The situation wherein a cured material reverts toward its original pre-cured condition, (e.g., a cured potting compound that reverts to a sticky, liquid-like consistency).
Stress Force divided by cross-sectional area.
Symbols The following definitions apply to warnings, cautions, and notes found throughout this advisory circular (AC):
WARNING: An operation or maintenance procedure, practice, condition, statement, etc., which if not strictly observed, could result in injury to or death of personnel or long term (chronic) health hazards to personnel.
CAUTION: An operation or maintenance procedure, practice, condition, statement, etc., which if not strictly observed, could result in damage or destruction of equipment or loss of mission effectiveness.
NOTE: An operating procedure, practice, or condition, etc., which is essential to emphasize.
Tensile Strength Stress at which a material fails.
Total Environment The circumstances and conditions which surround and influence the equipment. The total environment includes manufacturing, handling, storage, shipping, mission, maintenance, and repair.
Appendix 3 Ultraviolet Light Light in a wavelength band ranging from the invisible wavelengths of about 4 nanometers (nm) to the border of the x-ray region at about 380 nm, just beyond the violet end of the visible spectrum.
Unacceptable Response A detrimental abnormality in system performance.
Undesirable Response A tolerated interruption of normal performance.
Wicking See Capillary Action.
Index
COMPREHENSIVE INDEX
SUBJECT PAGE A Abrasive Tools ......................................................................................................... 51, 53, 74, 95, 96
Aircraft Cleaning Compound Method184
Air Drying62
Alternate Cleaning Methods183
Aluminum ............................................................................. 8, 18, 32, 33, 34, 75, 121, 151, 163, 173
Aluminum Electrolytic Capacitors138
Aluminum Surface Treatment75
Anode ................................................................................................................................... 5, 17, 148
Definition5
Antenna Connectors ............................................................................................................... 120, 121
Antenna Mounting Area Preparation Procedures111
Antenna Systems ...................................................................................................................... 24, 111
Application of Coatings80
Application of Primer80
Application of Topcoat83
Aqueous Ultrasonic Cleaner52
ATE Cabinets, Doors, and Panels125
Atom5
Avionics Cleaning Equipment50
Avionics Cleaning Materials47
Avionics Cleaning Procedures54
Cleaning and Drying Restrictions ........................................................................................ 55, 56
Cleaning and Removal of Bacteria and Fungi58
Cleaning and Removal of Dust, Dirt, Grease, and Oil58
Cleaning and Removal of Silicone Lubricant .................................................................... 58, 130 Cleaning and Removal of Solder Flux Residue ....................................................... 37, 48, 57, 98
Fingerprint Removal57
Hand Cleaning Methods56
Hazardous Chemical or Material Identification Label ................................................... 49, 50, 73
Avionics Cleaning Equipment50
Cleaning Procedures54
Corrosion Cleaning Facility45
Hazards of Cleaning54
Materials Used for Cleaning46
Post-cleaning Procedures61
Pre-cleaning Criteria55
Solvent Ultrasonic Cleaner .......................................................................................... 53, 63, 127 Special Considerations ......................................................................................................... 26, 61 Surface Preparation ...................................................................................................... 59, 78, 149
Water Base Solvent Spray Booth51
When To Clean54
Avionics Test Equipment124
Index B
Basic ESD Precautions176
Battery Compartment ....................................................................................................... 21, 100, 126
Battery Compartments, Boxes, and Adjacent Areas100
Beryllium Copper163-168
Bilge Areas ........................................................................................................................... 21, 39, 99
Bimetallic Junctions148
Black Plague35
Bonding/Ground Connection Electrical Resistance Test124
Electronic Equipment Shock Mount158
Preservation ................................................................................. 45, 64, 123, 125, 139, 158, 184
Boric Acid Neutralizing Solution101
Bromothymol Blue Indicating Solution ................................................................................. 100, 103 Litmus Indicating Solution .............................................................................................. 100, 103
Preparation of Solution for Cleaning and Neutralizing Battery Electrolytes100
C Cadmium ................................................................................................ 8, 18, 32, 100, 121, 148, 149
Catastrophic Failures175
Cathode ......................................................................................................................................... 6, 15 Chemical Conversion Material Procedures .......................................................................................... 74, 75
Magnesium Surface Treatment76
Post-Treatment of Conversion Coated Surfaces77
Surface Treatment .................................................................................................................. 9, 74
Treatment of Other Metals77
Cleaning Neutralizing Procedure .................................................................................................... 102, 103 Priority ............................................................................................................................. 181, 182 Surface Preparation ........................................................................................ 59, 78, 96, 149, 171
Versus Calibration124
Coaxial Connectors ........................................................................................ 6, 53, 65, 119, 120, 145 Cockpit Cockpit and Control Boxes ...................................................................................... 105, 106, 136
Cockpit Area Components188
Compounds Electrolyte ................................................................................. 5, 6, 13, 15-17, 44, 100, 125, 169 Electron .............................................................................................................. 5, 6, 87, 169, 172
Electron Conductor6
Galvanic Couple .................................................................................................................... 6, 17 Ion .......................................................................................................................................... 6, 15
Condensed Moisture11
Copper ......................................................................... 7-10, 33-35, 148, 151-158, 163-166, 169, 171 Corrosion Aluminum Surface Treatment .............................................................................................. 32, 75
Effects of Solder Flux37
Effects on Metals32
Effects on Nonmetals36
Factors Influencing6
Index
Fatigue19
Prevention Philosophy21
Preventive Maintenance and Control20
Prone Areas21-26
Electromechanical25
Electronics ........................................................................................... 25, 31, 83, 90, 91, 162 Moisture and Other Fluid Intrusion Sources ...................................................... 21, 24-26, 32 Special Considerations .................................................................................................. 26, 61 Structural ......................................................................................... 24, 74, 77, 108, 111, 146 Resistant Steel ............................................................................................................. 32, 151-156
Theory5
Anode .................................................................................................................. 5, 6, 15, 148 Atom .................................................................................................................................. 5, 6 Cathode ................................................................................................................ 6, 15, 18, 33 Visual Inspection . 28-31, 58, 60, 98, 111, 126, 133, 139, 141, 142, 144-146, 169-171, 187-189, 193, 194 Corrosive Conditions and Elements ................................................................................. 8, 10, 13, 44
Condensed Moisture11
Man-made Environments13
Micro-organism, Insect, and Animal Attack .................................................................. 13, 31, 38 Moisture ............................................................................................................................ 7-11, 13 Other Fluids ......................................................................................................................... 11, 21 Pressure ................................................................................................................................ 11, 13 Temperature ................................................................................................................. 8, 9, 11, 13 Crevice Corrosion ....................................................................................................................... 15, 16 D
Damaged Items194
Discharge Sensitive Equipment172
Desiccants70-72
Direct Failures175
Disassembly Inspection Procedures193
Dissipation of Static Charges176-178
ESD Protection Guidelines176-180
Drying and Preservation of Non-removable Avionics equipment ................................... 190, 191 Drying ..................................................................................................................................... 184, 185
Air Drying62
Coated Equipment88
Preparation62
Preservation Procedures184-186
Solvent Vapor Drying63
with Circulating Air Oven ............................................................................................. 62, 63 with Forced Air Oven ............................................................................................ 63, 98, 184 with Hot Air Blower .................................................................................................... 62, 185 with Vacuum Oven ................................................................................................ 63, 89, 185
Index E Edge Connectors and Mating Plugs ............................................................................... 130, 137, 145 Effects of Corrosion ............................................................................................................ 24, 25-28, 31-44
Dust/Lint Accumulation44
Insect and Animal Attack38
Microbial Attack37
Electrical Bonding and Grounding Straps ........................................................................................ 109, 130
Bonding/Grounding Connections148-158
Bimetallic Junctions148
Hardware ................................................................................................... 148, 151, 153, 156
Connector and Wave guide Caps69
Connectors and Receptacles191
Equipment Shock Mount Bonding Preservation158
Motors and Generators188
Electrolyte ....................................................................................... 5, 6, 13-17, 19, 44, 100, 125, 126
Electron Conductor6
Electrostatic Voltages174
Emergency Cleaning Procedures ......................................................................................... 182-184, 192-195
Aircraft Cleaning Compound184
Alternate Methods ..................................................................................................... 183, 184
Primary Method183
Solvent Method183
Water-Displacing Method .................................................................................. 184, 186-191 Drying and Preservation .................................................................................................. 184, 185
Drying and Preservation Procedures185
Heated Compartment185
Hot Air Blower185
Vacuum Oven Drying185
Vented Drying Oven185
Vented Drying Oven (Bulb Type)185
Preparations181
Emergency Reclamation Team.................................................................................. 181, 192
Production Planning182
Required Tools, Materials, and Equipment182
Reclamation Team Organization181
EMI
Definition159
Precipitation Static162
Protection Maintenance168-171
Shielding Structures162-165
Shielding Design Goals162
Types of Protection162-168
Encapsulates83-98
Drying of Coated Equipment88
Fungus-Proof Coating86-89
Fungus-Proof Varnish86
Methods of Application88
Index
Potting Compounds83-86
Sealant ....................................................................................................................... 84, 85, 90-92
Special Precautions89
Environmental Conditions .......................................................................................................... 10, 21
Environmental Factors10
Equipment Bays ..................................................................................................... 29, 30, 47, 99, 100 Equipment Hinges and Latches .............................................................................................. 108, 109 ESD
Corrosion Inspection and Repair180
Definition172
Direct Failures175
Packaging Practices ......................................................................................................... 177, 180
Protection Guidelines178
Susceptible Equipment175
Workstation Shop Practices ............................................................................................. 177, 180
Evaluation of Corrosion Damage31-44
Exfoliation Corrosion19
External Corrosion Removal and Cleaning ...................................................................... 77, 140, 141
External Mounted Equipment105
F
Factors Influencing Corrosion6
Moisture Intrusion ......................................................................................................... 6, 9-12, 21 Failure Mechanisms ............................................................................................................... 174, 175 ESD-Related Failure of Components ............................................................................... 174, 175 Filters .............................................................................................................................. 145, 162, 168
Fingerprint Removal57
Flush or Dome Antenna Mountings ....................................................................................... 119, 120
Frames, Mounting Racks, and Shock Mounts103
Fretting Corrosion16
Fungus-Proof
Coatings86
Varnish86
Fuselage Shielding162
G Galvanic Corrosion ........................................................................................................... 17, 121, 169 Galvanic Couple ........................................................................................................................... 6, 17
Generation of Static Charges172-174
General Inspection Procedures30
Gold and Gold Plating ........................................................................................... 8, 10, 16, 18, 33-35 H
Hand Cleaning Methods56
Handling ............................................................. 10, 13, 24, 45, 46, 68, 69, 73, 77, 78, 121, 132, 176 Hardware Selection ................................................................................................................ 148, 149
Hazardous Chemicals and Waste Generation49
Hazards of Cleaning54