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1. For lead acid battery spills, use the litmus solution, which will change in color from deep blue to red in any area that is contaminated with battery acid.
2. For nickel-cadmium battery spills, use the Bromothymol Blue Indicating Solution, which will change in color from amber or gold to a deep blue in any area that is contaminated with potassium hydroxide.
(c) Using a pump spray bottle with the proper neutralizing solution, spray the entire area where the indicating solution showed a change in color. Ensure the area is well saturated and that the stream is directed into all seams and crevices where the battery electrolyte could collect. Use care to prevent liquids from spreading to adjacent areas and ensure that bilge area drains are open to allow fluids to flow overboard. Allow the neutralizing solution to remain on the surface for at least 5 minutes or until all bubbling action ceases.
(d) Rinse the area thoroughly with a liberal amount of clean water and remove any standing liquid or puddles, as in subparagraph (a).
(e) Reapply the indicating solution as in subparagraph (b). If the solution does not change color, rinse the area as in subparagraph (d) and dry the area with a clean cloth or rags. If the solution changes color, repeat subparagraphs (c), (d), and (e).
(f) Corrosion Preventive Compound, as discussed in Chapter 4, paragraph 407, may be used to displace any moisture or temporarily preserve any bare metal until the area is properly protected.
(g) Repair or apply, as required, prepaint treatment, paint coatings, and sealant per Chapters 4 and 5. Special acid and/or alkali resistant coatings are usually required for battery compartments, boxes, and surrounding areas. Refer to the OEM’s maintenance instruction manual.
e. Frames, Mounting Racks, and Shock Mounts. Shock mounts and associated hardware on pod or airframe mounted equipment are usually the last items to be inspected for corrosion damage. Figure 6-3 shows evidence of a moisture entrapment area on the avionics shelf and corrosion on equipment racks and shock mounts. These inspections normally require the removal of shock mounts to facilitate a thorough examination. For this reason, shock mounts, their associated racks, and hardware should be preserved after inspection to ensure protection from the elements. For frames, mounting racks, and shock mounts that are not normally painted, remove corrosion and preserve as follows:
(1) Remove corrosion with 320-grit abrasive cloth, conforming to A-A-1048, or abrasive nylon mat, conforming to A-A-58054, Type I. Pay particular attention to dissimilar metal couples.
NOTE: The use of dissimilar metals in the selection of screws, washers, and nuts should be minimized wherever possible. See Chapter 7 for information on bonding and grounding hardware.
Par 602 Page 104
(2) Clean the affected area with Isopropyl Alcohol, TT-I-735. Apply with a clean cloth or cheesecloth. Pay particular attention to the rubber shock absorbers of the shock mounts. The rubber may swell if saturated with Isopropyl Alcohol, TT-I-735. If the rubber shock mounts do swell, they should return to normal size in a short time after the Isopropyl Alcohol, TT-I-735, evaporates.
(3) For frames, mounting racks, and shock mounts that are normally painted, remove corrosion and clean as indicated in steps (1) and (2). Conversion coat, prime, and paint in accordance with the OEM’s maintenance instructions and the procedures of Chapter 5, paragraphs 503 and 504.
(4) Frames, mounting racks, shock mounts, and associated hardware should be preserved with a thin film of Water-Displacing Corrosion Preventive Compound, identified in Chapter 4, paragraph 407, and Table 4-4. Corrosion Preventive Compound, conforming to MIL-DTL-85054, is recommended for lasting protection.
FIGURE 6-3. MOISTURE ENTRAPMENT AREA AND CORRODED FRAME,
MOUNTING RACKS, AND SHOCK MOUNTS
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f. External Mounted Equipment. External mounted equipment is susceptible to the same corrosive environment as the airframe. Internal and external cleaning techniques are the same as for the airframe except for electromagnetic gaskets, shields, electrical connectors, and mating surfaces. Treat these areas as follows:
NOTE: See Chapter 8 and the OEM’s maintenance manual for information on electromagnetic gaskets and mating plating where the plating surfaces may have been removed.
(1) Remove corrosion and clean in accordance with subparagraph 602g.
(2) Conversion coat, prime, and paint in accordance with the OEM’s maintenance manual and the procedures of Chapter 5, paragraphs 503 and 504.
(3) Clean and preserve electrical connectors in accordance with subparagraph 603k.
(4) If the application of conversion coating, primer, and paint cannot be accomplished, temporarily preserve the external surfaces with a thin film of Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054. For internal surfaces, apply a thin film of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type II.
g. Cockpit and Control Boxes. Cockpits are susceptible to dirt, grime, and corrosive attack from cooling air and general human occupancy. The following inspection, cleaning, and treatment procedures should apply to the cockpit and avionics components.
(1) Use a vacuum cleaner to clean the cockpit area of dirt and dust. Pay particular attention to the areas under and behind control boxes.
(2) Inspect control box units for corrosion and contaminants. Pay particular attention to switches, dials, knobs, electrical connectors, control box and instrument panel mating surfaces, and attaching fasteners.
(3) Remove corrosion products from metal surfaces using an abrasive nylon mat, conforming to A-A-58054, Type I, or an appropriate cleaning and polishing pad.
(4) Clean the affected area with an approved solvent or Dry Cleaning Solvent, MIL-PRF-680, Type II, and a clean cloth or cheesecloth.
NOTE: Local air pollution regulations may restrict the use of this solvent.
Comply with all local air pollution regulations.
WARNING: Dry Cleaning Solvent, MIL-PRF-680, is flammable and toxic to the eyes, skin, and respiratory tract. Skin and eye protection is required.
Avoid repeated or prolonged contact. Use only in well-ventilated areas. Keep away from open flames or other sources of ignition.
(5) Following solvent cleaning, perform a final wipe using a clean cloth or cheesecloth and Isopropyl Alcohol, TT-I-735.
Par 602 Page 106
(6) Repaint or touch-up existing paint as required in accordance with the OEM’s maintenance instructions manual or the procedures of Chapter 5, paragraphs 503 and 504.
(7) Apply a thin film of Water-Displacing Corrosion Preventive Compound, MIL-PRF-81309, Type II, on exterior metal surfaces and wipe off any excess with a clean cloth or cheesecloth. Do not get preservative on the acrylic plastic faceplates of instruments.
(8) Clean and preserve toggle, rotary, and push-button switches in accordance with subparagraph 603k.
(9) Clean control box faceplates with a solution of 1 ounce nonionic liquid detergent, conforming to MIL-D-16791, Type I, and 1 gallon of clean water. Wipe faceplates with a clean, soft flannel cloth or cheesecloth and the nonionic liquid detergent solution. Dry and polish the glass faceplate with a clean, soft flannel cloth or cheesecloth.
(10) Clean and preserve cockpit and control box electrical connectors in accordance with subparagraphs 603k(2) through (5).
(11) Hardware (panel fasteners, clamps, etc.) is generally replaced if found corroded.
FIGURE 6-4. TERMINAL BOARD INSTALLATION
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h. Terminal Boards, Junction Boxes, Relay Boxes, and Circuit Breaker Panels.
Remove covers and access panels, as required. Figure 6-4 shows a typical terminal board installation. Treat corrosion and preserve as follows:
WARNING: Ensure that all electrical power is disconnected from the aircraft and all electrical systems in the aircraft are deactivated. Disconnect all batteries.
(1) External Surfaces:
(a) Inspect, clean, and treat in accordance with subparagraph 602k.
(b) If the application of conversion coating, primer, and paint cannot be accomplished, temporarily preserve the external surfaces with a thin film of Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054.
(2) Internal Surfaces and Components:
(a) Remove corrosion with an abrasive nylon mat, conforming to A-A-58054, Type I.
(b) Clean the affected area by wiping or brushing with Isopropyl Alcohol, TT-I-735. While the surface is still wet, perform a final wipe with a clean cloth or cheesecloth and allow the surface to air dry.
(c) Clean and preserve electrical connectors in accordance with subparagraphs 603k(2) through (5).
(d) Preserve internal surfaces of terminal boards, junction boxes, relay boxes, and circuit breaker panels by applying a thin film of Water-Displacing Corrosion Preventive Compound conforming to MIL-PRF-81309, Type III. Avoid applying preservative to relays and circuit breaker contact points.
i. Metallic Equipment Covers and Housings. Avionics equipment cases, covers, housings, and associated hardware can also be exposed to harsh environmental elements. Inspect, clean, treat, and preserve in accordance with subparagraph 602b, except for the following:
(1) Hardware (fasteners, clamps, etc.) is generally replaced if found corroded.
(2) Hinges and latches on equipment covers should be preserved and lubricated in accordance with subparagraphs 602k(6) and (7).
j. Nonmetallic Covers and Housings. In some cases, avionics equipment, support equipment, and general test equipment use nonmetallic high-impact plastic, fiberglass, Kevlar, or graphite/carbon epoxy covers and housings. These should be inspected and cleaned, and the paint touched-up as follows:
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(1) Inspect nonmetallic covers and housings for structural damage (cracks and delaminations), corrosion around metallic hardware, hinges, latches, and damaged paint.
(2) Repair any structural damage per the OEM’s maintenance instructions.
(3) Inspect hardware, hinges, and other metal attachments for signs of corrosion.
Remove any corrosion with 320-grit abrasive cloth, conforming to A-A-1048, or an abrasive nylon mat, conforming to A-A-58054, Type I.
(4) Clean nonmetallic covers and housings with a solution of 9 parts fresh water and 1 part Aircraft Cleaning Compound, conforming to MIL-PRF-85570, Type II. Apply with a brush or clean cloth.
(5) Rinse with fresh water and wipe dry with a cleaning cloth.
(6) Touch-up paint finish in accordance with Chapter 5, paragraph 504.
(7) Lubricate and preserve hinges and latches per subparagraph 602k.
(8) Preserve unpainted metallic hardware, hinges, and latches in accordance with Chapter 4, paragraph 407.
k. Equipment Hinges and Latches. Inspect hinges and latches on equipment boxes, doors, and covers for corrosion and proper operation. Treat as follows:
(1) Clean hinges and latches with a cleaning cloth dampened with an approved solvent.
(2) Remove corrosion with 320-grit abrasive cloth, conforming to A-A-1048, or an abrasive nylon mat, conforming to A-A-58054, Type I.
(3) Wipe residue with a clean cloth dampened with Isopropyl Alcohol, TT-I-735, and allow to air dry.
(4) Clean and treat bare aluminum and magnesium hinges and latches in accordance with Chapter 4, subparagraph 405m, and Chapter 5, paragraph 503.
WARNING: Chemical conversion material is flammable and toxic to the eyes, skin, and respiratory tract. Skin and eye protection is required. Avoid repeated or prolonged contact. Use only in well-ventilated areas. Keep away from open flames or other sources of ignition.
CAUTION: Exercise care when using chemical conversion materials near electronic hardware. The solutions can cause corrosion of delicate electronic devices not suitably protected.
(5) Touch up paint finish in accordance with Chapter 5, paragraph 504.
(6) Lubricate hinges and rotating latches as follows:
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(a) Spray hinges and latches at pivot points with Water-Displacing Corrosion Preventive Compound, MIL-PRF-81309, Type II.
NOTE: The purpose of Water-Displacing Corrosion Preventive Compound is to displace any entrapped water between hinge and latch components. The subsequent application of a lubricating oil may then fill the void areas and provide lubrication. Without the Water-Displacing Corrosion Preventive Compound, the lubricating oil will not displace the entrapped water because it is less dense than the water.
(b) Apply Lubricating Oil, General Purpose Preservation, conforming to MIL-PRF-32033, to all moving parts.
(7) Preserve unpainted metallic hardware, hinges, and latches not requiring lubrication per Chapter 4, paragraph 407.
l. Shelves, Bulkheads, and Crevices. Inspect shelves, bulkheads, crevices, and corners for signs of dust, lint, debris, and corrosion. Figures 6-5 and 6-6 show lint and debris accumulation on a shelf. Pay particular attention to cracked, chipped, peeling, or deteriorating paint and sealant. Treat in accordance with subparagraph 602b.
m. Moisture Traps and Cavity Areas. Inspect for moisture traps and cavities at the rear of equipment shelves. Figure 6-3 shows evidence of a moisture entrapment area on the avionics shelf. Treat in accordance with subparagraph 602b.
(1) Moisture traps and cavities may be filled with Sealing Compound, conforming to MIL-PRF-81733, when authorized.
(2) Apply sealant and finish in accordance with Chapter 5, paragraphs 504 and 505.
n. Electrical Bonding and Grounding Straps. Bonding and grounding straps used on aircraft and avionics equipment may exhibit galvanic corrosion when not protected. Figure 3-8 and Figure 6-7 show examples of a corroded bonding strap and attach hardware. In most cases the material used for bonding and grounding straps is different than the mating surfaces of the aircraft and avionics equipment. Treat these areas in accordance with Chapter 7, paragraph 702.
Par 602 Page 110 FIGURE 6-5. LINT ACCUMULATION ON A SHELF
Par 602 Page 111 FIGURE 6-6. LINT AND DEBRIS ACCUMULATION ON A SHELF
603.
REPAIR OF AVIONICS SYSTEMS, EQUIPMENT, AND COMPONENTS.
a. Antenna Systems. Antenna systems are normally exposed to fairly severe environments. Without adequate corrosion protection, these systems can fail via shorts, open circuits, loss of dielectric strength, signal attenuation, poor bonding, or electromagnetic interference (EMI). Structural damage to the aircraft can also result. Antennas mounted on the fuselage require openings in the aircraft structural skin to route the various cables to the antenna.
The area around the antenna mounting is susceptible to moisture intrusion from rain, runway deicing fluids/materials, condensation, aircraft wash, and internal fluids (i.e., fuel, oil, lavatory and galley products, etc.). Antennas mounted on the lower fuselage are particularly susceptible to corrosion. The inspection and treatment process is outlined in the following paragraphs.
(1) Visual Corrosion Inspection. A visual examination of installed antennas and mounting areas can reveal evidence of a corrosion attack. Cracks, splits, and peeling of the exterior paint finish and sealant are a good indicator of possible corrosion damage. Evidence of corrosion deposits at the antenna mounting areas is the most obvious indication that an attack has taken place. Examine for a grayish-white to white powdery deposit (aluminum oxide). Figure 6-8 shows a corroded antenna mounting area and electrical plug.
(2) Antenna Mounting Area Preparation Procedures. When corrosion is visually evident or highly suspected, corrective action, including further inspection by disassembly, is
Par 603 Page 112 necessary to determine the full extent of any damage and prevent further deterioration. Corrosion treatment includes stripping exterior finishes in the affected area, removing corrosion products, cleaning, and applying surface treatment for avionics bonding. The recommended procedures that may be used on the antenna base and mating aircraft structure for corrosion removal, cleaning, and mounting preparation are as follows:
(a) Remove dirt, grime, oil, and grease from antenna mating surfaces using a cleaning cloth or cheesecloth dampened with an approved solvent. A clean surface will allow proper evaluation of the extent of corrosion damage. Figure 6-10 shows a corroded antenna mounting area on a removed lower fuselage skin.
(b) Remove existing fillet sealant from the mating surface of the antenna and aircraft structure/skin with a nonmetallic scraper (see Figure 6-9).
(c) Remove paint as required from the area surrounding the antenna mounting with an epoxy paint remover as described in Chapter 5, paragraph 502.
(d) Thoroughly clean the stripped area with a water-moistened cleaning cloth or cheesecloth.
(e) 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. Ensure complete corrosion removal from the antenna base and mating aircraft surface.
(f) Wipe off corrosion removal products using a cleaning cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow the surface to air dry.
(g) If bare metal was exposed on the antenna base or aircraft structure/skin, treat the cleaned surface with an avionics grade Chemical Conversion Coating conforming to MIL-DTL-81706, Class 3, in accordance with Chapter 5, paragraph 503.
Par 603 Page 113 FIGURE 6-7. CORRODED BONDING STRAP AND ATTACH HARDWARE
Par 603 Page 114 FIGURE 6-8. CORRODED ANTENNA MOUNTING AREA AND ELECTRICAL PLUG