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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
Par 603 Page 115 FIGURE 6-9. NONMETALLIC SEALANT REMOVAL TOOLS NO TE: 1. All dimensions are in inches unless otherwise specified.
2. Material: Micarta suggested.
Par 603 Page 116 FIGURE 6-10. CORRODED ANTENNA MOUNTING AREA (
3) Rigid Antenna Mounting (without gasket). The mounting bases of rigid antennas vary in shape and size. The following installation procedures are typical and may be used for mast-type antennas (blade, spike, whip base, or long wire mast base) not requiring a gasket.
Figures 6-11 and 6-12 show typical blade mounted antennas. The recommended procedures for the application of corrosion prevention measures and attachment of the antenna to the aircraft structure/skin are as follows:
(a) Clean and remove any corrosion from the antenna base and aircraft structure/skin as described in subparagraph 603a(2).
(b) Remove corrosion from screw fastener countersinks and fastener bore areas on the antenna base in order to provide good electrical conductivity from the base to the screw fasteners. 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.