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(6) Radar Dish Antenna Corrosion Prevention Procedure. One of the primary problems related to dish antennas is the integrity of the protective finish. The protective finish is subject to scratches and chipping from normal maintenance and handling. The metal used in antenna construction is usually aluminum or magnesium. Both metals are anoxic to the attached hardware and subject to galvanic corrosive around the hardware. The dish and remainder of the mount are subject to surface corrosion when the finish is damaged. Spot touch up, as required, the paint finish in accordance with the instructions of Chapter 5, paragraphs 502 and 503.
Complete paint stripping, cleaning, and refinishing is normally justified if 20 percent of the paint finish is damaged. There are some radar antennas that have a protective finish or covering of Mylar over the base aluminum or magnesium. For these types of antenna dishes, refer to the OEM’s maintenance instructions.
(7) Temporary Dish Protection. This procedure is appropriate for line maintenance personnel to repair limited, minor surface damage of the finish to the dish. The procedure is also appropriate as an alternate procedure to paint touch-up until paint can be applied.
(a) Remove surface corrosion to the limits of the OEM’s maintenance instructions with 320-grit abrasive cloth, conforming to A-A-1048, or an abrasive nylon mat, conforming to A-A-58054, Type I.
(b) Wipe off corrosion products using a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow the surface to air dry.
(c) Spray a coat of Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054, on the affected area(s).
NOTE: Unless the area is subject to a significant amount of abrasion from operation or handling, MIL-DTL-85054 can provide up to a year of protection.
(8) Radar Antenna Hardware. For protection of the radar antenna hardware, such as nuts, bolts, screws, washers, and clamps, utilize the following procedure:
(a) Clean hardware with a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow surfaces to air dry.
NOTE: Replace nuts, bolts, screws, washers, and clamps which have worn off their protective coatings (normally cadmium).
(b) If corrosion is present but replacement is not practical, the corrosion may be removed using 320-grit abrasive cloth, conforming to A-A-1048, or an abrasive nylon mat, conforming to A-A-58054, Type I. Repeat step (a) following corrosion removal.
(c) Spray a coat of Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054, on the affected hardware after installation.
(9) Antenna Connectors. Antenna connectors require special procedures to avoid moisture entry and corrosion damage. Corrosion is by far the principal cause of antenna
Par 603 Page 122 performance deterioration. Clean and preserve antenna connectors, both multipin and coaxial, in accordance with subparagraphs 603k(2) through (5).
(10) Ultrahigh Frequency (UHF)/Very High Frequency (VHF)/Automatic Direction Finder (ADF) Antenna Sealing. The location of UHF/VHF/ADF antennas is normally on the lower fuselage. Figure 6-10 shows a corroded antenna mounting area on a removed lower fuselage skin. These mounting locations are particularly susceptible to corrosion because of fluid entrapment in bilge areas. This fluid entrapment is the principal reason for additional maintenance requirements for these types of antennas. The following preventive measures should be utilized to minimize this problem.
(a) With the antenna removed, clean the antenna and the mounting location on the aircraft of grease, oil, and dirt using a clean cloth or cheesecloth dampened with an approved solvent or the cleaning procedures described in Chapter 4, paragraph 405.
(b) Remove corrosion deposits to the limits of the OEM’s maintenance instructions with 320-grit abrasive cloth, conforming to A-A-1048, or an abrasive nylon mat, conforming to A-A-58054, Type I.
(c) Wipe clean corrosion removal areas on the antenna and aircraft skin/structure with a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow surfaces to air dry.
(d) Install the UHF/VHF/ADF antennas per the OEM’s maintenance instructions.
The following procedures may be used as an alternative.
(e) (Alternate installation procedures.) Normally, antennas are assembled with the dustcover mated to the bottom of the antenna casting. A plate called the antenna element mates to the antenna cavity flange under a plastic plate. During reassembly of the antenna components, discard the extruded rubber dust cover channel which fits between the dustcover edge and the antenna casting (this area will be sealed with sealant). Wipe the circumference of the mated dustcover and antenna casting clean, using a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Additionally, clean around the circumference of the plastic plate which mates to the antenna cavity and the attached fastener heads. Allow all surfaces to air dry.
(f) Mask as required, using pressure-sensitive tape.
(g) Seal the junction of the dustcover, antenna cavity, and antenna casting outer edge with Polysulfide Sealing Compound, conforming to MIL-PRF-81733, Type II. Mix sealant in accordance with the manufacturer’s instructions (see Chapter 6, subparagraph 603a(6)). Apply sealant with a spatula or extrude a bead of sealant using a sealant gun. Additionally, seal around the circumference of the plastic plate, antenna cavity, and the attach fastener heads for the dustcover. Remove any masking tape within the working time of the sealant.
(h) Allow the sealant to cure (tack-free) as stated in the manufacturer’s instructions.
Install the antenna in accordance with the OEM’s maintenance instructions.
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(i) Spray a coat of Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054, on the antenna mount.
(j) Clean and preserve the electrical connectors in accordance with the instructions of subparagraphs 603k(2) through (5).
(k) Mask as required the antenna and aircraft surfaces using pressure-sensitive tape.
(l) Mix sealant in accordance with the manufacturer’s instructions. Apply sealant to the circumference of the antenna and aircraft skin/structure with a spatula or extrude a bead of sealant from a sealant gun (see Chapter 6, subparagraph 603a(6)). Smooth sealant using a spatula. Within the working time of the sealant, remove any masking tape. Allow the sealant to cure prior to flight. Figures 6-11 and 6-12 show examples of properly mounted and sealed blade mounted antennas.
(11) Long Wire and Direction Finder (DF) Sense Antenna Corrosion Prevention Procedures. The cleaning and preservation procedures for this type of antenna are as follows:
NOTE: If the long wire is the stranded type, and the corrosion is more extensive than light surface corrosion, it is normal practice to replace the wire. Stranded wire has the propensity of wicking corrosives through capillary action, causing extensive damage that may not be readily apparent.
(a) Cleaning and corrosion procedures for individual parts prior to mounting the antenna are described in subparagraph 603a(2), while antenna mounting procedures are described in subparagraph 603a(3).
(b) Wipe clean all antenna parts with a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow surfaces to air dry.
(c) Assemble long wire or DF antenna parts and install in accordance with the OEM’s maintenance instructions.
(d) After installing and tensioning the antenna, spray a coating of Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054, over the attached hardware.
If a new bare wire (no nylon sleeve) was installed, wipe the wire with a clean cloth or cheesecloth soaked with Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054. This will allow the Corrosion Preventive Compound to penetrate around the individual wire strands.
NOTE: It is preferable to apply Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054, to a new bare wire after the antenna is installed and tensioned. If access to the wire is impractical after installation, wet-wipe the wire with MIL-DTL-85054 prior to installation. In such cases, minimize flexing, coiling, or abrading the wire after the Corrosion Preventive Compound has been applied and before the wire is installed and tensioned.
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(e) To prevent moisture intrusion into the insulator, fill the space around the wire where it enters the insulator with room temperature vulcanizing (RTV) sealant, conforming to MIL-A-46146, Type I; RTV 3140 (clear) is recommended. Use the cleaning and application procedures of Chapter 5, subparagraphs 505d(8) and (9). Seal both ends of the insulator in this manner.
(12) Bonding/Ground Connection Electrical Resistance Test.
NOTE: Select a scale on the milliohm meter that will allow a reading of
2.5 milliohms around mid-scale. This will ensure maximum instrument accuracy. Proper torque on the connections, good resistance readings, and complete sealing of the antenna installation are all essential to ensure the antenna will function properly in service.
(a) The electrical resistance test is performed after an antenna base is mounted or ground installation is assembled. The test should take place prior to the application of sealant.
The test uses a milliohm meter to obtain resistance readings between the antenna base or grounded portion of the antenna and the aircraft skin/structure. It is essential that the test probe be placed against bare metal when taking the readings.
(b) The maximum allowable resistance reading between the antenna base or grounded portion of the antenna and the aircraft skin/structure is 2.5 milliohms.
b. Avionics Test Equipment. Precision measurement and test equipment is required for testing, troubleshooting, and repairing avionics components and systems. This makes the reliability of this equipment in any environment critical to safe aircraft flight and system functions. Aircraft operational requirements often result in short troubleshooting and repair times for malfunctioning avionics systems. Valuable maintenance time is lost if this equipment is not functioning properly. A major source of test equipment malfunction is corrosion on contacts.
Corrosion sources that are particularly detrimental to avionics test equipment include moisture and fluid intrusion (rain, condensation, fuel, hydraulic fluid, etc.), corrosive elements in the surrounding atmosphere, malfunctioning or inadequate shop environmental control systems, and malfunctioning or inadequate built-in filter systems.
NOTE: In this section, use of the term “avionics test equipment” shall refer to all aircraft electrical and electronic system test equipment. This includes support equipment, oscilloscopes, signal generators, meters, Automatic Test Equipment (ATE), and any other equipment used to perform measurements on test, or troubleshoot avionics equipment.
(1) Cleaning Versus Calibration. A problem common to all automatic/manual test equipment is the effect of dirt, dust, lint, etc., on equipment calibration. A large quantity of test equipment, particularly older equipment, is possibly not maintained (cleaned, calibrated, etc.) on a scheduled basis. This lack of maintenance allows contaminants to collect on the components and become an integral part of the circuit, thus altering circuit parameters. These contaminant-induced changes are compensated for during each re-calibration process and can limit the equipment’s peak operating efficiency over time. Additionally, the calibration of
Par 603 Page 125 equipment can shift in service if some of the contaminants become dislodged. Because of the effect that contaminants have on electrical characteristics, immediate cleaning and preservation is mandatory after exposure of the equipment to any of the following conditions:
(a) External exposure to wet weather conditions.
(b) Internal exposure to water or any other fluids.
(c) Internal or external exposure to fire extinguishing agents.
(d) Internal or external exposure to electrolytes or corrosive deposits from batteries.
(2) Support Equipment and General Purpose Test Equipment Covers and Housings. The inspection, cleaning, corrosion removal, and preservation of support equipment and general purpose test equipment covers and housings should be performed as follows:
NOTE: Prior to cleaning covers and housings, remove the operator’s panel, electrical and electronic components, harnesses, and connectors.
(a) Inspect, remove corrosion, clean, treat, paint, and preserve in accordance with subparagraph 602b.
(b) Hardware associated with test equipment housings and covers that are not normally painted should be preserved in accordance with subparagraph 602e(4).
(c) Equipment covers with hinges and latches should be lubricated and preserved in accordance with subparagraphs 602k(6) and (7).
(3) ATE Cabinets, Doors, and Panels. Inspection, cleaning, corrosion removal, and preservation of ATE cabinets, doors, and panels should be performed as follows:
NOTE: The use of dissimilar metals in the selection of screws, washers, and nuts should be eliminated whenever possible. See Chapter 7 for information on bonding and grounding hardware.
(a) Inspect hardware and electrical bonding locations for signs of galvanic corrosion. Pay particular attention to dissimilar metal couples.
(b) Remove corrosion, clean, treat, and paint in accordance with subparagraph 602b.
(c) Hardware associated with ATE cabinets, doors, and panels that are not normally painted should be preserved as often as required in accordance with subparagraph 602e(4). Do not preserve water seal gaskets.
(d) Equipment covers with hinges and latches should be lubricated and preserved in accordance with subparagraphs 602k(6) and (7).
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(4) Battery Compartments. Some support equipment and general purpose test equipment contain internal batteries. Clean, neutralize, and preserve the battery compartment as follows:
(a) Clean and neutralize electrolyte spills in accordance with subparagraphs 602d(1) through (6).
(b) Inspect, clean, treat, and paint the battery compartment in accordance with Chapter 5, subparagraphs 504a through 504f.
(c) When painting of the battery compartment is not practical, temporarily preserve the area in accordance with subparagraph 602e(4).
(5) Meters. Voltmeters, ammeters, and multimeters are usually constructed of high-impact plastic or acrylic. Normally these meters are not disassembled for cleaning. Clean the exterior surfaces as follows:
(a) Clean metal hardware and metal surfaces with cotton swabs and a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow the surface to air dry.
(b) Apply a coating of Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054, on metal hardware. Take the necessary steps to avoid getting preservative on acrylic plastic face plates.
(c) Clean toggle, rotary, and push-button switches in accordance with subparagraph 603g.
(d) Clean meter face plates in accordance with subparagraph 602g(9).
(e) Clean high-impact plastic or acrylic housings with a 1 ounce solution of nonionic liquid detergent, conforming to MIL-D-16791, Type I, in 1 gallon of water. Clean the surface with a clean cloth or cheesecloth wet with the detergent solution. When the surface is clean, remove the detergent solution by wiping the surface with a clean cloth or cheesecloth that has been dampened with clean water. Rinse the cloth frequently.
(6) Operator and Instrument Panels. Support equipment, general purpose test equipment, and ATE operator instrument panels should be inspected, cleaned, treated, painted, and preserved as follows:
(a) Visually inspect operator and instrument panels for corrosion and contaminants.
Pay particular attention to switches, dials, knobs, and hardware.
(b) Remove corrosion using an abrasive nylon mat, conforming to A-A-58054, Type I.
(c) Clean metal surfaces with cotton swabs and a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow the surface to air dry.
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(d) Apply a coating of Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054, on metal hardware. Take the necessary steps to avoid getting preservative on acrylic plastic face plates.
(e) Treat and paint operator and instrument panels in accordance with Chapter 5, subparagraphs 504a through f.
(f) Clean toggle, rotary, and push-button switches in accordance with subparagraph 603g.
(g) Clean meter face plates in accordance with subparagraph 602g(9).
(h) Clean and treat light bulb assemblies in accordance with subparagraph 603e.
(7) Internal Cleaning of Support Equipment. With the exception of emergency procedures described in Chapter 10, the internal cleaning of support equipment is normally a function of a repair activity or the OEM. The recommended cleaning and preservation techniques for support equipment are as follows:
(a) Remove covers and housing.
(b) Inspect for oil, grease, hydraulic fluids, and corrosion. Additionally, inspect for components that can act as water and solvent traps. Chapter 4, Table 4-3, lists components that may pose a problem with water and solvent entrapment.
(c) Seal, bag, or remove potential components that may entrap water and solvent.
Chapter 4, subparagraph 405f, describes sealing methods.
(d) Remove oil, grease, and hydraulic fluids using a solvent ultrasonic cleaner. See the ultrasonic cleaning instructions in Chapter 4, subparagraph 404d, and Table 4-2. Solvent ultrasonic clean for 15 seconds and solvent dry for 3 minutes.
(e) Remove corrosion with a mini-abrasive cleaning tool in an approved cleaning booth using technical grade sodium bicarbonate (see Chapter 4, subparagraph 404e).
(f) If no corrosion, oils, greases, or hydraulic fluid were noted in the inspection, clean the internal areas of the support equipment with a water detergent solution as described in Chapter 4, subparagraph 404b.
(g) Treat and paint internal areas of the support equipment in accordance with Chapter 5, subparagraphs 504a through f.
(h) On areas that are not painted but require preservation, apply a thin coat of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type III.
Take necessary steps to avoid getting preservative on components that should not be preserved.
(See Chapter 4, subparagraphs 407d and 407e, and Table 4-4.)
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(8) Internal Cleaning of General Purpose Test Equipment. Oscilloscopes, signal generators, frequency counters, etc., usually accumulate more dust and dirt than other contaminants. Internal cleaning and preservation of general purpose test equipment should be accomplished as follows:
(a) Remove covers and housing.
(b) Inspect for oils, grease, dust, dirt, and corrosion. Additionally, inspect for components that can act as water and solvent traps. Chapter 4, Table 4-3, lists components that may pose a problem with water and solvent entrapment.
(c) Seal, bag, or remove potential components that may entrap water and solvent.
Chapter 4, subparagraph 405f, describes sealing methods.
(d) Use a vacuum cleaner to remove loose dust, dirt, and lint from the internal chassis and circuit components.
(e) Remove corrosion with a mini-abrasive cleaning tool in an approved cleaning booth using technical grade sodium bicarbonate (see Chapter 4, subparagraph 404e).
(f) If no corrosion, oils, or greases were noted in the inspection, clean the internal areas of the general purpose test equipment with a water detergent solution as described in Chapter 4, subparagraph 404b.
(g) Treat and paint internal areas of the support equipment in accordance with Chapter 5, subparagraphs 504a through f.
(h) On areas that are not painted but require preservation, apply a thin coat of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type III.
Take necessary steps to avoid getting preservative on components that should not be preserved.
(See Chapter 4, subparagraphs 407d and 407e, and Table 4-4.)
(9) Internal Cleaning of ATE. ATE is usually constructed so that circuits are installed in drawers or cabinet-type racks. Attempting to clean the entire drawer or cabinet could prove difficult because of the size and weight of the assembly. Where the assemblies can be moved and mechanically cleaned, use the procedures of subparagraph 603b(8). Those assemblies that cannot be moved and mechanically cleaned should be cleaned and preserved as follows:
(a) Open cabinet doors, remove the cover, and slide drawers to the fully extended position.
(b) Inspect for oil, grease, dust, dirt, and corrosion. Additionally, inspect for components that can act as water and solvent traps. Chapter 4, Table 4-3, lists components that may pose a problem with water and solvent entrapment.
(c) Seal, bag, or remove potential components that may entrap water and solvent.
Chapter 4, subparagraph 405f, describes sealing methods.
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(d) Use a vacuum cleaner to remove loose dust, dirt, and lint from the internal chassis, wiring, and circuit components. Avoid direct contact between the vacuum cleaner hose wand and any delicate circuit components.
(e) Hand clean in accordance with Chapter 4, subparagraph 405g, using a water detergent solution as described in subparagraph 404b(5), or Isopropyl Alcohol, TT-I-735.
CAUTION: If wire wrap circuit board construction is used in ATE, do not apply water detergent solutions or solvents. In wire wrap installations only vacuuming of dirt, dust, and lint is authorized. Do not apply preservation materials to wire wrap circuit boards.
(f) On areas that are not painted but require preservation, apply a thin coat of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type III.
Take necessary steps to avoid getting preservative on components that should not be preserved (see Chapter 4, subparagraphs 407d and 407e, Table 4-4, and the caution statement for the preceding, subparagraph 603b(9)(e)).
(10) Internal Cleaning of Microwave Test Equipment. Microwave equipment contains many potential water and solvent entrapment areas. In addition, microwave equipment makes use of many acrylic vanes and lenses in wave guides and cavities, variable attenuators, etc. Generally, these components can be sealed or removed from the chassis prior to cleaning and drying. Internal cleaning and preservation of microwave test equipment should be performed as follows:
(a) Clean the external surface in accordance with subparagraph 603c.
(b) Clean the internal surface in accordance with subparagraph 603c.
(c) Inspect the wave guide for corrosion.
(d) Remove corrosion from external surfaces using an abrasive nylon mat, conforming to A-A-58054, Type I. Wipe off residue with a clean cloth or cheesecloth. Do not disturb the center connector with a cleaning tool or brush.
(e) Clean connector sections by spraying internal and external areas with Isopropyl Alcohol, TT-I-735. Do not disturb the center connector with a cleaning tool or brush. Wipe excess solvent dry with a clean cloth. Allow the section to air dry.
(f) If the wave guide will not be installed immediately, seal the ends of the section with OEM protective caps or pressure-sensitive tape, conforming to MIL-T-22085.
(g) Preserve external areas of the wave guide section with a thin coat of Corrosion Preventive Compound, conforming to MIL-DTL-85054.
CAUTION: Do not apply preservative materials to internal surfaces or areas of wave guide sections or angled physical contact (APC) connectors.
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(11) Special Cleaning Procedures. The following test equipment circuit components should be cleaned, lubricated, and preserved as follows:
(a) Bonding and Grounding Straps. Clean and preserve electrical bonding and grounding straps in accordance with Chapter 7, paragraph 702.
(b) Relays and Circuit Breakers. Clean and preserve relays and circuit breakers in accordance with subparagraph 603f.
(c) Rotary Switches, Trim Potentiometers, and Sliding Cam Switches. Clean, lubricate, and preserve rotary switches, trim potentiometers, and sliding cam switches in accordance with subparagraph 603g, and as follows:
1. Apply Spray Cleaning and Lubricating Compound, conforming to MIL-PRF-29608, Type I, to the internal portion of the switch.
CAUTION: Do not apply Spray Cleaning and Lubricating Compound, MIL-PRF-29608, to printed circuit boards (PCB) or other areas where soldering may be required. This material contains silicone which is difficult to remove and prevents proper adhesion of any material applied to the sprayed area.
2. While the surface is still wet, wipe sliding contacts, cams, and contact points with a clean cotton swab or pipe cleaner as required, to remove dirt, dust, and other residue.
3. Spray cleaned areas that require lubrication with Spray Cleaning and Lubricating Compound, conforming to MIL-PRF-29608, Type I. A silicone lubricant residue will remain. Do not apply preservative materials.
(d) Microminiature PCBs. Clean microminiature PCBs as follows:
1. Hand clean microminiature PCBs of dirt, dust, and other residue with a clean cotton swab or a soft bristle brush wet with Isopropyl Alcohol, TT-I-735, in accordance with Chapter 4, subparagraph 405g.
2. Rinse the microminiature PCBs with deionized water.
3. Dry the microminiature PCBs in accordance with Chapter 4, subparagraph 406e.
(e) Multipin Electrical Connectors and PCB Edge Connectors. Clean, treat, and preserve multipin electrical connectors and PCB edge connectors in accordance with subparagraph 603h, and subparagraphs 603k(1) through (4).
(f) Sliding Attenuators, Variable Attenuators, and Tunable Cavities. Clean, treat, and preserve as follows:
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1. Remove corrosion and tarnish by lightly rubbing with Magic Rub Plastic or a wooden pencil eraser. Care should be taken not to remove the thin plating on the surface.
2. Clean the area by applying Isopropyl Alcohol, TT-I-735, with an acid brush. Rinse the area with Isopropyl Alcohol, TT-I-735, and wipe dry with a clean cloth or cheesecloth. Allow the component to air dry.
CAUTION: Sliding and variable attenuators and tunable cavities are natural water and solvent traps. Do not leave these components exposed during internal equipment cleaning. Clean the exterior of sliding and variable attenuators and tunable cavities by hand where the cleaning solution, rinse water, or solvent can be properly dried.
3. Lubricate sliding components with an application of Spray Cleaning and Lubricating Compound, conforming to MIL-PRF-29608, Type I. Mask any nearby areas where the presence of the silicone lubricant is not desired. Silicone is very difficult to remove and prevents proper adhesion of any material applied to the sprayed area (use Chapter 4, subparagraph 405j).
4. Spray a thin coating of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type III, on external metal surfaces. Avoid placing preservative material on sliding components.
(g) Internal Surfaces of Sliding Attenuators, Variable Attenuators, and Tunable Cavities. Clean internal surfaces of sliding attenuators, variable attenuators, and tunable cavities as follows:
1. Hand clean the slide area(s) by applying Isopropyl Alcohol, TT-I-735, with an acid brush.
CAUTION: Sliding and variable attenuators and tunable cavities are natural water and solvent traps. Do not leave these components exposed during internal equipment cleaning. Clean the interior surfaces of sliding and variable attenuators and tunable cavities by hand only where the cleaning solution, rinse water, or solvent can be properly dried. Do not apply preservative material to internal slide surfaces.
2. Rinse the area with Isopropyl Alcohol, TT-I-735, and wipe dry with a clean cloth or cheesecloth. Allow the component to air dry.
(12) Painting Systems. It is important that the metallic housings of avionics test equipment be protected from the environment. A properly applied paint system provides effective long-term protection. These paint systems can be degraded by abrasion, chipping, scratching, and other forms of in-service damage. When damage to the paint finish occurs, immediate action should be taken to restore protection to the base metal. Restore corrosion protection as follows:
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(a) Temporary Protection.
1. Clean the bare area with a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow the surface to air dry.
2. Spray a thin coating of Corrosion Preventive Compound, MIL-DTL-85054, to the clean, bare area.
(b) Paint Finish Restoration. Inspect, clean, treat, and apply protective paint finish in accordance with subparagraph 602b. The paint color selection should be in accordance with the OEM’s maintenance instructions.
NOTE: Paint color matching is a difficult process. Paint from the same manufacturer, color number, and batch number will not match the same paint applied earlier that has been allowed to age and weather.
(13) Packaging, Handling, and Storage. The packaging, handling, and storage procedures of Chapter 4, paragraph 409, should apply to test equipment. The following additional requirements should also apply.
(a) Wipe down test equipment on a regular basis using a clean, dry, soft cloth. This will prevent accumulation of soils and potentially corrosive materials on the equipment.
Additionally, clean equipment generally receives better handling treatment from the user.
(b) Ensure all appropriate caps are installed on equipment cavities and connections.
(c) Ensure all decals, calibration stickers, part numbers, and serial numbers are kept legible and up to date.
(d) Test equipment should be stored and shipped in the appropriate carrying case in accordance with Chapter 4, subparagraph 409d.
c. Wave Guides. Wave guides are only effective if the internal surfaces are clean and free of damage (dents) and corrosion (surface or pitting). Wave guide mounting and flange seal integrity must be maintained; otherwise, the electrical characteristic of the wave guide will be adversely affected. Currently, there is no method of preserving the internal surface of the wave guide except by plating another metal, such as gold or silver, during the manufacture of the wave guide. This plating process is expensive. Wave guides used in aircraft are generally not plated.
The method of protecting the internal finish on a wave guide is to prevent moisture intrusion.
Moisture intrusion can occur any time the wave guide seal is broken and opened for maintenance. Wave guides that must be opened should be sealed at the flanged ends with an appropriate cap or pressure-sensitive tape. Prior to assembly, all residue from the pressure-sensitive tape should be removed. The following describes methods for cleaning, removing corrosion, and preserving external wave guide surfaces.
(1) Ensure the ends of the wave guide are sealed using an appropriate cap or pressure-sensitive tape.