Par 603 Page 145 CAUTION: Corrosion Preventive Compound, MIL-DTL-85054, cures to a hard, permanent finish. Once cured, it is difficult to remove with Isopropyl Alcohol, TT-I-735, or other approved solvents. Repeated application of MIL-DTL-85054 should be avoided. For connectors requiring frequent disconnecting and connecting, use Corrosion Preventive Compound, MIL-PRF-81309, Type III, in lieu of MIL-DTL-85054.
l. Coaxial Connectors. Coaxial connectors require special steps in order to avoid water intrusion. In most cases, water intrusion in the fuel/oil quantity indicator and similar capacitance type indicating system connectors will cause erroneous quantity indications on cockpit instruments. Antenna coaxial connectors can generate similar erroneous signals when water intrusion in those connectors occurs. Coaxial connectors should be inspected, cleaned, and treated in accordance with subparagraphs 603k(2), (3), and (5).
m. Wire Harnesses and Cables. When corrosion is found at the pin-to-wire connection on electrical connectors, plugs, and receptacles, the wire harnesses and cables should be inspected for corrosion, cracking, and other damage to the wire insulation. Wire harnesses and cables should be inspected, cleaned, and treated as follows:
(1) If corrosion is apparent at the back of the connector, it may be necessary to remove an inch or two of the wire harness cable cover to inspect for corrosion.
(2) Visually inspect the rear of the connector at the wire-to-pin connection for corrosion damage. Inspect the wire harness cover for tears and separations, and wiring and wiring insulation for cracks, corrosion, and burn indications.
(3) Apply Isopropyl Alcohol, TT-I-735, with a typewriter brush or toothbrush. Scrub the affected area until contaminants are loosened. Reapply Isopropyl Alcohol, TT-I-735, as required, to flush the area of the contaminants.
(4) Shake excess solvent from the wire harness and wipe dry with a clean cloth or cheesecloth.
(5) Where applicable, repair the wire harness and cable covering.
(6) Treat, as required, connecting electrical connectors and plugs in accordance with subparagraph 603k.
n. PCBs. Edge connectors (and mating plugs) used in miniature and microminiature PCBs should be cleaned and preserved in accordance with subparagraph 603h.
o. Filters. The cleaning of air filters is essential to maintaining the cleanliness and reliability of avionics and test equipment. The frequency of cleaning and method used will normally be specified in the OEM’s maintenance instruction manual. The frequency of cleaning may need to be increased if local environmental conditions dictate. Filters may be cleaned as follows:
Par 603 Page 146
(1) Place the filter in a deep sink and flush thoroughly with fresh water.
(2) Scrub the rigid or metal filters with a cleaning brush to remove dirt, grime, and lint.
(3) If oil or grease is present in the filter, clean the filter with a solution of 9 parts fresh water to 1 part Cleaning Compound, conforming to MIL-PRF-85570, Type II. Scrub the rigid or metal filters with a cleaning brush. Rinse thoroughly with fresh water.
(4) Blow off excess water with dry air or dry nitrogen at not more than 10 pounds per square inch (psi) pressure.
(5) Allow filter to air dry.
(6) Do not preserve filters.
p. Sensitive Internal Metal Surfaces. Metal surfaces such as resonant cavities, tube covers, and other delicate metal components should be visually inspected for signs of corrosion.
Remove corrosion, clean, and preserve as follows:
(1) Remove dirt and contaminants with a nonabrasive cleaning cloth. Scrub the affected area until all contaminants are dislodged.
(2) Remove corrosion and tarnish with a typewriter eraser or a pencil eraser. Care should be taken not to remove the thin plating from the surfaces.
(3) Clean the part of residue with Isopropyl Alcohol, TT-I-735. Apply with an acid brush or a typewriter brush.
(4) Remove residue with a clean cloth.
(5) Rinse the affected area with Isopropyl Alcohol, TT-I-735, and wipe dry with a clean cloth. This step will assist in removing any water.
(6) Air dry or dry with a hot air gun as described in Chapter 4, subparagraph 406d.
CAUTION: Exercise care when using a hot air gun near plastic materials.
Excessive heat may decompose the plastic and change its electrical characteristics.
(7) Preserve where circuit function will not be affected as follows:
(a) Spray a thin coating of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type III, on all metal surfaces. Avoid excessive application or overspray of preservative.
(b) Remove excess preservative by wiping with a clean cloth.
q. Static Discharge Wicks. Corrosion, deterioration, or structural damage to the static discharge wicks can result in poor performance from aircraft radios and communication systems,
Par 603 Page 147 erratic operation of instruments, and potential electrical shock to personnel. When damaged or corroded static discharge wicks are found, replace as follows:
(1) Remove and discard old static discharge wicks.
(2) Remove corrosion and contaminants from the mounting area with a nonabrasive pad. Scrub the affected area until all corrosion and contaminants are loosened.
(3) Clean the mounting area with Isopropyl Alcohol, TT-I-735, and an acid brush.
(4) Rinse the mounting area with Isopropyl Alcohol, TT-I-735, to flush out remaining residue.
(5) Wipe dry with a clean cloth. Allow the area to air dry.
(6) Chemically treat the mounting surface as described in Chapter 5, paragraph 503.
(7) Install the replacement static discharge wicks in accordance with the OEM’s maintenance instructions.
(8) Spray a thin coating of Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054, on all metal surfaces and attachment points. Avoid excessive application or overspray of preservative.
604 through 700. RESERVED.
Par 701 Page 148 CHAPTER 7. CORROSION CONTROL MEASURES FOR ELECTRICAL
BONDING/GROUNDING
701. ELECTRICAL BONDING/GROUND CONNECTIONS.
a. General. Electrical bonding provides a low resistance electrical path between two or more conductive units or components. Grounding is a form of bonding that utilizes the primary structure as a portion (return path) of the electrical circuit. Bonding may serve as one or all of the following functions:
(1) Provide a common ground for the proper electrical functioning of the units involved;
(2) Provide a path to minimize lightning strike damage;
(3) Prevent the buildup of static potentials that could result in a spark discharge;
(4) Minimize static and stray currents in units involved;
(5) Prevent a unit from emitting electromagnetic energy that would interfere with itself or other units (see Chapter 8); and
(6) Shield equipment from outside electromagnetic interference (EMI) sources.
b. Bimetallic Junctions. The connection of two or more diverse electrical objects often results in a bimetallic junction that is susceptible to galvanic corrosion. This type of corrosion can rapidly destroy a bonding connection through physical corrosion damage and the loss of the low resistance electrical path if suitable precautions are not observed. Refer to AC 43.13-1, Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair. Aluminum alloy jumpers (bonding straps) are used in many bonding situations. Copper, tin-plated copper, and stainless-steel jumpers are most often used to bond together aircraft and components parts made of stainless steel, cadmium-plated steel, aluminum, brass, or other metals. Where contact between dissimilar metals cannot be avoided, the choice of bonding material and associated attach hardware is important. When selecting materials for the bonding installation, the material(s) that is the most prone to corrosion (anode) should be the easiest and least expensive to replace. At bimetallic junctions, where finishes are removed to provide a good electrical connection, a preservative or sealant should be applied to the completed connection to prevent corrosion. This chapter describes and illustrates the procedures for the assembly and preservation of bonding or grounding connections. This includes special emphasis on techniques to minimize galvanic corrosion.
c. Hardware Selection. When repairing or replacing existing bonding or grounding connections, follow the Original Equipment Manufacturer’s (OEM) parts and maintenance instructions or use the same kind of bonding material and associated attach hardware as the original installation. The bonding material and associated attach hardware have been selected by the OEM for their mechanical strength, electrical requirements, corrosion resistance, and ease of installation. However, when a bonding or grounding connection installation displays evidence of galvanic corrosion after proper assembly, the installation of a sacrificial washer made of an
Par 701 Page 149 anoxic material between the dissimilar materials will allow that anoxic washer to corrode.
Replacement of the corroded washer is easy and the least expensive way of repairing the bonding or grounding connection. Figures 7-1 through 7-6 and their corresponding tables show proper assembly configurations and list hardware and materials in the order of assembly depending on the particular metal(s) of the structural and bonding or grounding connection. For example, a proper installation for the aluminum terminal and jumper configuration in Figure 7-1 shows a bolt secured as a mounting stud for a bonding or grounding connection through a flat structural surface. The structure in this case is an aluminum alloy and the bonding or grounding jumper, as mentioned, is also aluminum. The attaching hardware are cadmium-plated steel bolts or screws, aluminum washers, and cadmium-plated lockwashers and nuts.
702. BONDING/GROUNDING SURFACE PREPARATION.
a. Surface Preparation. Procedures for the preparation of metallic surfaces before mating electrical conductor(s) are as follows:
(1) Remove all dirt, oil, grease, and other contaminants from an area slightly larger than the bonding or grounding connection. The area to be cleaned should be a minimum of 1 1/2 diameters the size of the bonding or grounding connection. Use a clean cloth or cheesecloth dampened with an approved solvent or Dry Cleaning Solvent, MIL-PRF-680, Type II.
NOTE: Local air pollution regulations may restrict the use of this solvent.
Comply with all local air pollution regulations.
(2) If more vigorous contaminant removal is required, scrub with an acid brush and an approved solvent or Dry Cleaning Solvent, MIL-PRF-680, Type II.
(3) Wipe area dry with a clean cloth or cheesecloth.
(4) Remove, as required, paint, anoxic coating or conversion coating film, and any corrosion from the attachment area using an abrasive nylon mat, conforming to A-A-58054, Type I. Do not exceed the maximum depth allowed by the OEM maintenance instructions.
(5) Wipe area clean with a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow area to air dry.
(6) Apply chemical conversion coat to aluminum or magnesium as described in Chapter 5, paragraph 503.
(7) Remove all dirt, oil, grease, and other contaminants from the bonding cable terminal with a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735.
(8) If more vigorous contaminant removal is required, scrub with an acid brush and Isopropyl Alcohol, TT-I-735.
(9) Assemble bonding or grounding connection(s) and torque in accordance with the OEM’s maintenance instructions, or use Figures 7-1 through 7-6 as a guide.
Par 702 Page 150
(10) Perform an electrical resistance test as described in Chapter 6, subparagraph 603a(12).
FIGURE 7-1. STUD BONDING OR GROUNDING TO FLAT SURFACE Notes:
*See Table 7-1 for specific materials.
†Limited to a quantity of four (4).
Par 702 Page 151 TABLE 7-1. HARDWARE FOR STUD BONDING OR GROUNDING TO FLAT
SURFACE Structure Screw or Bolt and Lock Nut Plain Nut Washer A Washer B Washer C Lockwasher E Lockwasher F
ALUMINUM TERMINALS AND JUMPER Aluminum Alloys Cadmium- Plated Steel Cadmium- Plated Steel Aluminum Alloy Aluminum Alloy Cadmium- Plated Steel or Aluminum Cadmium- Plated Steel Cadmium- Plated Steel Magnesium Alloys Cadmium- Plated Steel Cadmium- Plated Steel Magnesium Alloy* Magnesium Alloy* Cadmium- Plated Steel or Aluminum Cadmium- Plated Steel Cadmium- Plated Steel Steel, Cadmium- Plated Cadmium- Plated Steel Cadmium- Plated Steel None None Cadmium- Plated Steel or Aluminum Cadmium- Plated Steel Cadmium- Plated Steel Steel, Corrosion- Resistant Corrosion- Resistant Steel Cadmium- Plated Steel None None Cadmium- Plated Steel or Aluminum Corrosion- Resistant Steel Cadmium- Plated Steel
TINNED COPPER TERMINALS AND JUMPER Aluminum Alloys Cadmium- Plated Steel Cadmium- Plated Steel Aluminum Alloy Aluminum Alloy Cadmium- Plated Steel Cadmium- Plated Steel Cadmium- Plated Steel or Aluminum Magnesium Alloys Caution: Do not connect copper to magnesium Steel, Cadmium- Plated Cadmium- Plated Steel Cadmium- Plated Steel None None Cadmium- Plated Steel Cadmium- Plated Steel Cadmium- Plated Steel Steel, Corrosion- Resistant Corrosion- Resistant Steel Cadmium- Plated Steel None None Cadmium- Plated Steel Corrosion- Resistant Steel Corrosion- Resistant Steel *When not available, use aluminum alloy.
Par 702 Page 152 FIGURE 7-2. NUT PLATE BONDING OR GROUNDING TO FLAT SURFACE Notes:
*See Table 7-2 for specific materials.
†Limited to a quantity of four (4).
Par 702 Page 153 TABLE 7-2. HARDWARE FOR NUT PLATE BONDING OR GROUNDING TO FLAT
SURFACE Structure Screw or Bolt and Nut Plate Rivet Lockwasher Washer A Washer B
ALUMINUM TERMINALS AND JUMPER Aluminum Alloys Cadmium-Plated Steel Aluminum Alloy Cadmium- Plated Steel Cadmium-Plated Steel Aluminum Alloy Magnesium Alloys Cadmium-Plated Steel Aluminum Alloy Cadmium- Plated Steel Cadmium-Plated Steel Magnesium* Alloy Steel, Cadmium-Plated Cadmium-Plated Steel Corrosion- Resistant Steel Cadmium- Plated Steel Cadmium-Plated Steel Aluminum Alloy Steel, Corrosion- Resistant Corrosion- Resistant Steel Corrosion- Resistant Steel Cadmium- Plated Steel Cadmium-Plated Steel or Aluminum Alloy Cadmium-Plated Steel
TINNED COPPER TERMINALS AND JUMPER Aluminum Alloys Cadmium-Plated Steel Aluminum Alloy Cadmium- Plated Steel Cadmium-Plated Steel Aluminum Alloy Magnesium Alloys Caution: Do not connect copper to magnesium Steel, Cadmium-Plated Cadmium-Plated Steel Corrosion- Resistant Steel Cadmium- Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Steel, Corrosion- Resistant Corrosion- Resistant Steel Corrosion- Resistant Steel Cadmium- Plated Steel Cadmium-Plated Steel Corrosion- Plated Steel or Corrosion- Resistant Steel *When not available, use aluminum alloy.
Par 702 Page 154 FIGURE 7-3. BOLT AND NUT BONDING OR GROUNDING No tes:
*See Table 7-3 for specific materials.
†Limited to a quantity of four (4).
Par 702 Page 155 FIGURE 7-4. COPPER JUMPER CONNECTOR TO TUBULAR STRUCTURE Notes:
*Inside surface of clamp (conduit) is cylindrical.
Par 702 Page 156 TABLE 7-3. HARDWARE FOR BOLT-AND-NUT Structure Screw or Bolt and Nut Plate Rivet Lockwasher Washer A Washer B
ALUMINUM TERMINALS AND JUMPER Aluminum Alloys Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel or Aluminum Alloy None Cadmium-Plated Steel or Aluminum Alloy Magnesium Alloys Cadmium-Plated Steel Chromium- Plated Steel Magnesium Alloys Magnesium* Alloys Cadmium-Plated Steel or Aluminum Alloy Steel, Cadmium-Plated Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel* Steel, Corrosion- Resistant Corrosion- Resistant Steel Corrosion- Resistant Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel
TINNED COPPER TERMINALS AND JUMPER Aluminum Alloys Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Aluminum Alloy Cadmium-Plated Steel Magnesium Alloys Caution: Do not connect copper to magnesium Steel, Cadmium-Plated Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Steel, Corrosion- Resistant Corrosion- Resistant Steel or Cadmium- Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel Cadmium-Plated Steel or Corrosion- Resistant Steel *When not available, use aluminum alloy.