Par 309 Page 43 FIGURE 3-14. LINT ACCUMULATION ON WIRING BUNDLE
Par 309 Page 44 FIGURE 3-15. LINT ACCUMULATION ON ELECTRICAL SWITCH
310.
EFFECTS OF DUST/LINT ACCUMULATION. Avionics equipment is subject to dust and lint accumulation. This condition is generally evident when the equipment has been installed for long periods of time and can become more severe with forced cooling air. In addition to the dust and lint accumulation from the movement of air, dust and lint can be attracted by magnetic fields from electric currents surrounding wiring and equipment. Dust can also accumulate on the surfaces of components and on the interior surfaces of components if that equipment has ventilating holes and louvers. The problem with accumulation of dust and lint is it will trap and hold moisture which can provide the electrolyte for corrosion and fungus growth (see Chapter 2, Paragraph 205, Corrosive Conditions). Additionally, dust and lint can degrade avionics equipment by being a conductor or an insulator. When dust and lint act as a conductor in the presence of moisture, they can provide a path for a current flow to either ground as a short or an unwanted circuit path between components. When dust and lint act as an insulator the avionics equipment can overheat causing premature failure. Severe accumulations of dust can appear as long stringy clumps, similar to Spanish moss hanging from trees, but on a smaller scale.
Figures 3-12 through 3-15 show examples of dust and lint accumulation. Frequent inspections and general cleaning of equipment will control the accumulation of dust and lint.
311 through 400. RESERVED.
Par 401 Page 45 CHAPTER 4. CLEANING AND PRESERVATION
401. GENERAL. The materials, equipment, and techniques described in this chapter are intended to assist the avionics technician at an avionics repair facility. This chapter discusses avionics cleaning and repair facility requirements, specialized support equipment to support cleaning, corrosion removal, drying of avionics equipment, and the different processes of cleaning, drying, preserving, packaging, handling, and shipping avionics equipment.
402. AVIONICS CORROSION CLEANING FACILITY. An avionics cleaning and repair facility should include as a minimum the following resources for the cleaning, drying, preserving, packaging, handling, and shipping of avionics equipment:
a. Adequate lighting and a temperature/humidity-controlled ventilation system.
b. Adequate space for safe operation of avionics cleaning and corrosion control equipment.
c. Operating instructions for each piece of equipment.
d. All hazardous materials (HAZMAT) and material safety data sheets (MSDS) for materials used.
e. Safety equipment and protective personal equipment as required by local, state, and Federal ordinances.
f. Personnel trained in the recognition of corrosion on avionics equipment as specified in this AC.
g. Personnel trained in the safe and proper operation of support equipment.
h. Quality assurance inspectors trained in the operational characteristics and restrictions of each piece of support equipment.
i. Avionics technicians who can recognize the various electrical and electronic equipment and components.
403. MATERIALS AND SUPPORT EQUIPMENT REQUIREMENTS.
a. General. Avionics technicians must understand the functions, capabilities, and restrictions associated with each piece of specialized support equipment, and the hazards of the cleaning and corrosion removal products and preservation materials. This knowledge will prevent injury to personnel and damage to avionics equipment and support equipment.
b. Materials. Consumable cleaning and corrosion removal products and preservation materials listed in Appendix 1 and Appendix 2 may be used as specified on avionics equipment if none were identified by the Original Equipment Manufacturer (OEM) or equipment operator.
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c. Materials Used For Cleaning. Table 4-1 contains a list of the various cleaning compounds and solutions, their characteristics, application, mixing instructions, and restrictions.
The cleaning of avionics equipment can be accomplished using the following processes:
CAUTION: Some of the materials identified in Table 4-1 can create hazardous conditions or damage equipment unless used strictly in the applications and manner described.
CAUTION: Some of the materials identified in Table 4-1 are chlorofluorocarbons (CFCs), an ozone depleting substance (ODS). These materials may be banned from use by environmental restrictions.
(1) Solvents are effective in dissolving greases and oils. Solvents can be applied by wiping, brushing, soaking, or spraying.
(2) Detergent and water in varying concentrations are used to remove dust, dirt, salt deposits, greases, and oils. Detergent and water cleaning mixtures can be applied by wiping, brushing, soaking, and spraying.
(3) Distilled or fresh water is used to dilute Isopropyl Alcohol or detergents for use in cleaning and as a final rinse. Water may also be used to remove dust, dirt, salt deposits, and cleaning solutions. Application is by wiping, brushing, soaking, and spraying.
Par 403 Page 47 TABLE 4-1. AVIONICS CLEANING MATERIALS Description Characteristics Application Restrictions Cleaning Compound, Aircraft Surface, MIL-PRF-85570, Type II General cleaning agent for light soil and dirt in equipment bays, on external cases, covers, and antenna assemblies.
Mix per manufacturer’s instructions or 1 part cleaner in 10 parts distilled water. Apply with cleaning cloth. Rinse with fresh water and wipe dry.
Do not use around oxygen fittings or oxygen regulators as fire or explosion may result.
Heavy concentrations of surface grime, oil, exhaust smudges, and fire extinguishing chemicals in equipment bays and on external cases and covers.
Mix per manufacturer’s instructions or 1 part cleaner in 6 parts distilled water. Apply with cleaning cloth. Rinse with fresh water and wipe dry.
Never use full strength.
Do not allow to dry on surface.
Detergent, Liquid, Nonionic MIL-D-16791, Type 1 Cleans transparencies, acrylic plastics, and glass.
Also used in the water-based Solvent Spray Cleaning Booth and Aqueous Ultrasonic Cleaner for removing contaminants.
For hand cleaning, apply with flannel cloth. Let dry; then remove with dry flannel cloth.
Mix per manufacturer’s instructions or 1 fluid oz.
per gallon of water.
Cleaning and Lubricating Compound, Electrical Contact, MIL-PRF-29608, Type 1 A cleaner-lubricant compatible with potting compounds, rubbers, and insulation. Contains 3 to 5% silicon. May be used for cleaning and lubricating electrical contacts.
Apply by spraying an even film to the surface.
Wipe clean with disposable applicator or pipe cleaner.
Do not use as a substitute for MIL-C-81302, Type I or Type II. Avoid application to areas requiring soldering or coating.
Cleaning Compound, Solvent, Trichlorotrifluoroethane, MIL-C-81302, Type II General cleaner for light to medium to heavy dirt, dust, contaminants, and fire extinguishing chemicals.
Used in the Solvent Ultrasonic Cleaner.
Do not use on acrylic plastics and acrylic conformal coatings. Do not use on unsealed aluminum electrolytic capacitors. Damage may result to end caps and cause leakage.
Dry Cleaning, Solvent, MIL-PRF-680, Type II General purpose cleaner for heavy dirt, dust, contaminants, and fire extinguishing chemicals in equipment bays and on external cases, covers, structural hardware, mounts, racks, etc.
Apply by wiping or scrubbing affected area with cleaning cloth, cheesecloth, or brush.
Wipe clean with cleaning cloth.
Do not use around oxygen, oxygen fittings, or oxygen regulator as fire or explosion may result.
Par 403 Page 48 Description Characteristics Application Restrictions Cleaner for smoke damage removal on internal chassis components.
Apply by scrubbing affected area with cleaning cloth, toothbrush, or typewriter brush. Wipe clean with cleaning cloth.
When used for smoke damage removal, always follow up with a solution of 1 part deionized water and 1 part Isopropyl Alcohol, TT-I-735.
Cleaner for smoke damage removal on circuit components and laminated circuit boards.
Apply by wiping or scrubbing affected area with cleaning cloth or toothbrush. Wipe clean with cleaning cloth.
May cause swelling of silicone rubber seals in equipment exposed for long periods.
Cleaner for removal of Water-Displacing Compound, MIL-PRF-81309, Type II or Type III, MIL-DTL-85054; and Corrosion Preventive Compound, MIL-PRF-16173, Grade 2, 3, and 4.
Apply by brush or toothbrush. Wipe clean with cleaning cloth.
May soften some plastics, wire harness tubing, and plastics coating on wiring. Test affected area for adverse reaction prior to general application.
Isopropyl Alcohol, TT-I-735 General purpose cleaner and solvent for removal of salt residue and contaminants common to internal avionics equipment. General cleaner for internal chassis components.
Apply a solution of 1 part deionized or distilled water and 1 part Isopropyl Alcohol, TT-I-735, to affected area with cleaning cloth or toothbrush.
Isopropyl Alcohol, TT-I-735, is highly flammable. All applications of Isopropyl Alcohol, TT-I-735, and water may be air dried or dried by portable air blower or oven.
Solvent cleaner for solder flux residue in all electronics, electrical equipment, and microminiature circuit applications.
Apply a solution of 1 part deionized or distilled water and 3 parts Isopropyl Alcohol, TT-I-735, and scrub the solder joint and adjacent area with an acid brush or toothbrush. Wipe clean with cleaning cloth.
Par 403 Page 49 Cleaner for bacteria and fungi attack on all metals and nonmetals.
Apply a solution of 1 part solvent Trichlorotrifluoroethane, MIL-C-81302, Type II, and 1 part Isopropyl Alcohol, TT-I-735, to affected area with cleaning cloth. Wipe clean and air dry.
Cleaner for saltwater immersion and fire extinguishing agents on all internal circuit components and laminated circuit boards.
Apply a solution of 1 part Isopropyl Alcohol, TT-I-735, and 9 parts solvent Trichlorotrifluoroethane, MIL-C-81302, Type II, to affected area with cleaning cloth, acid brush, or toothbrush.
Cleaner for electrical contact surfaces.
Apply a solution of 1 part deionized or distilled water and 1 part Isopropyl Alcohol, TT-I-735, to affected area with acid brush or pipe cleaner. Wipe clean and air dry.
Water, distilled Cleaner for solder flux residue in all electronics, electrical equipment, and microminiature circuit applications.
Apply a solution of 1 part deionized or distilled water to 3 parts Isopropyl Alcohol, TT-I-735, and scrub joint and adjacent area with acid brush or toothbrush. Wipe clean with cleaning cloth.
Deionized water is an acceptable substitute.
d. Hazardous Chemicals and Waste Generation. Many of the materials identified in this AC are hazardous and toxic to personnel not using appropriate personal protective equipment. These materials can also be potentially damaging to avionics equipment and aircraft if used in improper concentrations or misapplied. Prior to using any chemicals such as paint strippers, detergents, solvents, conversion coatings, primers, or paints, personnel should review the appropriate MSDS for warnings and cautions or the HAZMAT identification labels on the containers. Figure 4-1 provides a simple system of readily recognizable and easily understood markings which will give, at a glance, the general idea of the inherent hazards of any HAZMAT.
Additionally, the use of materials identified in this AC can, if improperly used or disposed of, create a hazard and contaminate the environment. Avionics technicians should use only the proper amount when mixing materials, close containers when not in use, use only the required amount to complete the intended procedure, and properly dispose of all materials in accordance with all Federal, state, and local regulations.
5/30/01/ AC 43-206 FIGURE 4-1. NFPA 704 WARNING SYSTEM LABEL
HEALTH HAZARD FIRE HAZARD 4 - Deadly Flash Points 3 - Extreme 4 - Below 73°F danger 3 - Below 100°F 2 - Hazardous 2 - Below 200°F 1 - Slightly 1 - Above 200°F hazardous 0 - Will not burn 0 - Normal material
REACTIVITY SPECIFIC 4 - May detonate HAZARD 3 - Shock and heat may detonate Oxidizer OXY 2 - Violent chemical Acid ACID change Alkali ALK 1 - Unstable if Corrosive COR heated Use NO WATER 0 - Stable
404. AVIONICS CLEANING EQUIPMENT.
a. The following paragraphs identify the different types of avionics cleaning equipment and list their uses and specific restrictions for those pieces of equipment. Table 4-2 lists the recommended cleaning process versus the type of avionics equipment.
NOTE: Avionics technicians should refer to the appropriate equipment service manual for specific operating instructions. Ultrasonic cleaning of printed circuit boards (PCB) is generally not authorized due to the difficulty in determining which component on the board will be susceptible to damage.
CAUTION: Miniature and microminiature PCBs may be susceptible to damage from the ultrasonic frequency, power level, or both.
Par 403 Page 50
Par 404 Page 51
b. Cleaning Booth, Water-Based Solvent Spray. The water-based solvent spray booth is used for the removal of dirt, dust, salt spray deposits, and loose corrosion deposits. The cleaning action is accomplished by a detergent and spray system.
TABLE 4-2. RECOMMENDED CLEANING PROCESS VERSUS TYPE OF AVIONICS
EQUIPMENT Type of Equipment Aqueous Ultrasonic Solvent Ultrasonic Water-based Spray Booth Abrasive Tool Mini- Abrasive Hand Clean Housings/covers X X X X X X Chassis X X X X X X Racks/mounts X X X X X X Control boxes X X(1) X X X Instruments X(1) X Light assemblies X X X X(1) X X Wave guides X X X X X X Servos/synchros X(1) X Antenna, blade X X X X X Antenna, dome X(1) X(1) X X(1) X X Antennas, radar X X(1) X X Motors X X(1) X X(1) X X Generators X X(1) X X(1) X X Batteries X Circuit breaker panels X X X X X Gyroscopes X(1) X(1) X Plugs, connectors X X X High-density connectors X X Edge connectors X X X Coaxial connectors X X X Printed circuit boards X X Note: (1) External use only
(1) The spray equipment provides an air pressure powered spray of a detergent/water solution through a handheld spray gun. The water used can be either filtered or tap water. The equipment can also deliver rinse water or a drying jet of air through the gun.
(2) The spray booth may provide for a turntable which allows 360-degree rotation of the avionics equipment being cleaned or rinsed.
Par 404 Page 52
(3) The spray booth operation may be used as a precleaner prior to placing the component in another cleaning process.
(4) The spray booth operation may be used to rinse components after other cleaning processes.
NOTE: Increasing the proportion of detergent in the cleaning solution does not necessarily increase the cleaning power of the detergent. This action can, in some cases, reduce cleaning effectiveness and cause corrosion.
(5) The preferred detergent for the water-based solvent spray booth should conform to MIL-SPEC MIL-D-16791, listed in Appendix 1. The detergent solution should be mixed in accordance with the manufacturer’s instructions or one ounce per gallon of water.
(6) Sealed bearings, synchro and servo bearings, instrument bearings, and similar devices with permanently lubricated (sealed) bearings can experience cleaning solution intrusion and the removal of the lubricant. These components could be rendered useless unless the processing procedures protect those components from degeneration or the lubricant is replaced.
(7) Sealed components (other than hermetically sealed) can trap the detergent and water solution. This may cause drying problems. In each case, the sealed component should be opened and inspected for trapped detergent and water solution.
c. Aqueous Ultrasonic Cleaner. The aqueous ultrasonic cleaner is used for the removal of dirt, dust, salt spray deposits, and loose corrosion deposits. The cleaning action is accomplished by the ultrasonic scrubbing action of the detergent and water solution.
(1) The maximum operating temperature should not exceed 130 °F (54 °C). The maximum operating frequency used should be 20 kilohertz (kHz).
(2) Presoaking avionics equipment and components prior to the ultrasonic function is an additional function of this equipment.
(3) The preferred detergent for the aqueous ultrasonic cleaner conforms to MIL-SPEC MIL-D-16791.
(4) Paper capacitors and paper bound components disintegrate in the detergent and water solution.
(5) Sealed bearings, synchro and servo bearings, instrument bearings, and similar devices should be treated per subparagraph 404b(6).
(6) Sealed components (other than hermetically sealed) should be treated per subparagraph 404b(7).
(7) Thin metal foil types of gummed labels can loosen and separate.
Par 404 Page 53
d. Solvent Ultrasonic Cleaner. The solvent ultrasonic cleaner is used to remove light to heavy oil, grease, and hydraulic fluid contamination by ultrasonic scrubbing in a solvent solution.
(1) Use only an approved solvent in the solvent ultrasonic cleaner. The maximum operating temperature should be the solvent’s boiling point. The maximum operating frequency used should be 40 kHz.
(2) Solvent degreasing, solvent vapor rinsing, and solvent vapor drying are additional functions of the solvent ultrasonic cleaner. Solvent degreasing is performed by solvent ultrasonic action in the degreaser tank. Solvent vapor rinsing (part of the degreasing function) is performed by a solvent vapor cloud. The solvent vapor cloud is created by a cooling coil placed near the top of the degreaser tank. Solvent vapor drying is also performed by the solvent vapor cloud.
(3) The solvent ultrasonic cleaner normally has a solvent degreaser tank. The solvent vapor rinse and solvent vapor drying function do not use the ultrasonic frequency function.
Therefore, they may be used to rinse and dry PCBs.
(4) Some acrylics may be susceptible to damage from the solvents used in solvent ultrasonic cleaners. Coaxial connector gaskets and other neoprene rubber components are susceptible to damage by some solvents. Refer to the manufacturer’s instructions or use another non-solvent cleaning process. See Table 4-3 for other restrictions.
(5) Sealed bearings, synchro and servo bearings, instrument bearings, and similar devices with permanently lubricated bearings should be treated as described in subparagraph 404b(6).
(6) Sealed components (other than hermetically sealed) should be treated as described in subparagraph 404b(7). The sealed component should be opened and inspected for trapped solvent.
e. Abrasive Cleaning Tools. Abrasive cleaning tools such as portable mini-abrasive units and blast cleaning cabinets are used to remove corrosion and corrosive products.
(1) The abrasive blast medium used in abrasive cleaning tools can easily be trapped in miniature and micro miniature female edge connectors. When working on components where these connectors are installed, the connectors should be sealed with pressure-sensitive tape. Upon completion of the cleaning process, ensure the tape is removed.
(2) Delicate metal surfaces, such as metal plating, are susceptible to damage from indiscriminate, unauthorized use of abrasive cleaning tools. Only properly trained personnel are authorized to use abrasive cleaning tools on avionics equipment.
(3) Some miniature/micro miniature PCBs contain electrostatic discharge (ESD)-sensitive devices (Chapter 9). These ESD sensitive devices may be destroyed by the static charge created in the rapid movement of air and abrasive agents in the abrasive cleaning tools.
Therefore, abrasive cleaning tools are not authorized on components where ESD-sensitive devices are installed.
Par 405 Page 54
405. AVIONICS CLEANING PROCEDURES.
a. General. Corrosion products and contamination by other sources previously described in Chapter 2 and this chapter are responsible for numerous problems and failures in avionics equipment. Proper cleaning can prevent many of these problems and is the next logical step after the initial inspection. Cleanliness is very important in maintaining the functional integrity and reliability of the avionics system and components. Corrosion products and contaminants can be either conductive or insulating. As a conductor they may provide undesirable electrical paths, and as an insulator they may interfere with the avionics equipment or systems operation. The following paragraphs contain information and suggested procedures for the cleaning of avionics equipment.
b. Cleaning Method Selection Criteria. The best technique for selecting a cleaning method is to select the mildest cleaning method that will accomplish the task. The selection of the cleaning method is a decision that may be outlined in an OEM’s maintenance manual or made by authorized personnel at the avionics equipment repair station. The decision on the mildest cleaning method should consider the following:
(1) Certain circuit components can be damaged by support equipment and cleaning solutions and solvents;
(2) Type and extent of the corrosion damage or contamination;
(3) Accessibility to the corrosion damage or contamination; and
(4) Type of avionics equipment.
c. Hazards of Cleaning. As previously mentioned, it is a good maintenance practice to use the mildest cleaning method that will ensure the removal of the corrosion or the contamination. It is also important that the correct cleaning solutions and cleaning materials be used to avoid further damaging the avionics equipment. The following items are offered to emphasize some of the hazards that can occur during cleaning of avionics equipment:
(1) Cleaning solvents or other cleaning materials can become trapped in crevices or seams of components or chassis. These trapped cleaning materials could then interfere with the application of protective coatings and result in the initiation of corrosion.
(2) Vigorous or prolonged scrubbing of laminated circuit boards can cause damage to the boards.
(3) Certain cleaning solvents can soften conformal coatings, wire insulation, acrylic panels, and PCBs.
d. When to Clean. The immediate removal of corrosion or contaminants on avionics equipment and the surrounding structure is always a high priority in a good Corrosion Prevention and Control Program (CPCP). Therefore, immediate cleaning should be accomplished on avionics equipment and components if they have been exposed to adverse weather, saltwater