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(2) Visually inspect the wave guide for evidence of corrosion.
NOTE: Wave guides are normally replaced if there is evidence of corrosion, either internally or on the mating surfaces.
(3) Remove corrosion on the exterior of wave guides using an abrasive nylon mat, conforming to A-A-58054, Type I.
(4) Remove protective caps or pressure-sensitive tape from mating flange surfaces.
(5) Wipe clean exterior surfaces and mating flange surfaces with a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow the surfaces to air dry.
(6) If the wave guide is not going to be installed immediately, install protective caps or apply pressure-sensitive tape to mating flange surfaces.
(7) If the wave guide is to be installed, connect in accordance with the OEM’s maintenance instructions.
(8) Preserve wave guides as follows:
(a) For wave guides that are not to be installed, spray a thin coating of Corrosion Preventive Compound, MIL-DTL-85054, on the exterior surfaces.
(b) For wave guides that will be installed, spray a thin coating of Corrosion Preventive Compound, MIL-DTL-85054, on the exterior surfaces and hardware after installation.
d. Wave Guide Feed Horns. Wave guide feed horns attached to some antenna dishes are subject to corrosive attack at the open end of the wave guide. To protect this open end area from corrosion, clean and preserve as follows:
(1) Wipe feed horn surfaces with a clean cloth or cheesecloth dampened with Isopropyl Alcohol, TT-I-735. Allow the surfaces to air dry.
(2) Spray the inner and outer throat area of the wave guide opening with an ultra-thin coat of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type III. Apply to exterior surfaces of the feed horn. For interior surfaces, direct the spray across the throat so that the spray is deposited on the opposite side (inner) of the feed horn and does not enter the wave guide past the flared throat area.
e. Lighting Systems and Assemblies. External formation lights, wing tip lights, rotating beacons, and anticollision lights are highly susceptible to corrosion. The corrosive attack is usually caused by poor seals which allow moisture intrusion from aircraft wash or from the environment in flight. Interior lights and equipment-mounted bulbs are also susceptible to corrosive attack. In most cases, corrosion will be heaviest at the base of the bulb because of the dissimilar metal contact between the bulb and the bulb socket. Clean and treat as follows:
Par 603 Page 134 WARNING: Ensure that electrical power is disconnected from the light assembly prior to corrosion removal and preservation procedures.
(1) Exterior Mounted Light Assemblies.
(a) Remove the light cover assembly and bulb from the socket in accordance with the OEM’s maintenance instructions.
(b) Remove corrosion using an abrasive nylon mat, conforming to A-A-58054, Type I. Scrub the affected area to loosen corrosion and contaminants.
(c) Clean the affected area with Isopropyl Alcohol, TT-I-735. Use an acid brush with the bristles trimmed back to assist in cleaning the base of the light socket.
(d) After cleaning, re-apply Isopropyl Alcohol, TT-I-735, to the light socket using a squeeze spray bottle to flush out any remaining residue.
(e) Wipe the light socket with a clean cloth or cheesecloth. Allow the area to air dry.
NOTE: The following procedures are applicable only to bulbs that are installed in their sockets with a turning, twisting, or scraping motion (screw base, bayonet base, or fuse-type clip). This scraping metal-to-metal contact is needed to ensure local displacement of the thin, soft film formed by Water-Displacing Corrosion Preventive Compound, MIL-PRF-81309, Type III.
(f) Preserve light assemblies as follows:
1. Apply a thin film of Water-Displacing Corrosion Preventive Compound, MIL-PRF-81309, Type III, to the metal base of the bulb and bulb socket.
2. Wipe to remove excess Corrosion Preventive Compound from the metal base of bulb using a clean cloth or cheesecloth.
3. Install the bulb in the bulb socket.
4. Preserve the outside area of the socket, light assembly, bare metal, and hardware by applying a thin film of Corrosion Preventive Compound, MIL-DTL-85054.
CAUTION: Allow the solvents in the Corrosion Preventive Compound to outgas prior to installing the light lens.
5. Assemble the light assembly. Touch up exterior paint finish as required and in accordance with Chapter 5, subparagraphs 504e and 504f.
(g) On lower fuselage light assemblies, water intrusion and entrapment is a problem during the aircraft wash; clean and preserve after each aircraft wash.
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(2) Interior Lights and Small Equipment Light Assemblies.
(a) Interior lights and small equipment assemblies should be cleaned and preserved in accordance with subparagraphs 603e(1)(a) through 603e(1)(f)3.
(b) Preserve the exterior of the light assembly using Water-Displacing Corrosion Preventive Compound, MIL-PRF-81309, Type II. Assemble the light assembly in accordance with the OEM’s maintenance instructions.
CAUTION: Allow the solvents in the Corrosion Preventive Compound to outgas prior to installing the light assembly.
f. Relay and Circuit Breakers. Remove corrosion and preserve as follows:
NOTE: Corrosion (tarnish) removal is required on most types of contacts.
Tarnish acts as an insulator on contacts. Sliding-type contacts have a self-cleaning action, and tarnish removal is not required if a bright surface area is visible. Relay and circuit breaker contact areas are usually plated with a highly conductive metal. Care should be taken to avoid removing this plating. If the plating is removed during cleaning, replace the relay or circuit breaker.
(1) Heavy corrosion and tarnish may be removed by rubbing with a typewriter eraser.
Medium corrosion and tarnish may be removed by rubbing with a pencil eraser.
(2) Rinse contacts with cotton swabs moistened with Isopropyl Alcohol, TT-I-735.
Clean the remainder of the relay or circuit breaker with an acid brush wet with Isopropyl Alcohol, TT-I-735. Pipe cleaners may be used in hard-to-reach areas to assist in swabbing residue.
(3) Remove Isopropyl Alcohol, TT-I-735, from relays or circuit breakers using a clean cloth or cheesecloth. Allow to air dry.
(4) Preserve relays and circuit breakers as follows:
(a) Apply a thin film of Water-Displacing Corrosion Preventive Compound, MIL-PRF-81309, Type III, to all areas of the relay or circuit breaker, avoiding contact and mating areas.
NOTE: After the application of preservative to relays and circuit breakers, it is necessary to ensure removal of the preservative material from all contact points and mating surfaces. Local air pollution regulations may restrict the use of this solvent. Comply with all local air pollution regulations.
CAUTION: Perform a final wipe of the contacts with Isopropyl Alcohol, TT-I-735, or the contacts will not function electrically.
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(b) Wipe the contact points and mating surfaces with a clean cloth, cotton swabs, or pipe cleaners (as applicable), dampened with an approved solvent or Dry Cleaning Solvent, MIL-PRF-680, Type II, to remove Corrosion Preventive Compounds. Perform a final cleaning wipe using a clean cloth, cotton swabs, or pipe cleaners (as applicable), dampened with Isopropyl Alcohol, TT-I-735.
g. Switches. Switches should include all cam-operated toggle, rotary, interlock, and push-button types. Remove corrosion and treat as follows:
NOTE: Local air pollution regulations may restrict the use of this solvent.
Comply with all local air pollution regulations.
CAUTION: Cleaning compounds and solvents may react with some encapsulants or plastics used to form wire harness tubing, wiring coating, conformal coatings, gaskets, seals, etc. Test on a small area for softening or other adverse reactions prior to general application (see Chapter 4, paragraph 405, and Table 4-3).
(1) Apply an approved solvent or Dry Cleaning Solvent, MIL-PRF-680, with an acid brush to remove contaminants.
(2) Wipe with a clean cloth or cheesecloth to remove excess solvent. Allow the switch to air dry.
(3) Switches should be preserved as follows:
NOTE: After the application of preservative to open switch assemblies, remove from the sliding contacts, cams, and contacts.
(a) Apply a thin film of Water-Displacing Corrosion Preventive Compound, MIL-PRF-81309, Type III, to the switch assembly. The cockpit and control box mounted switches should not be preserved on the exposed actuating arm or toggle. This area should be left clear of preservative so as not to hinder flight crew operation.
NOTE: After application of preservative to switches, it is necessary to ensure removal of the preservative material from the contact points and mating surfaces. Local air pollution regulations may restrict the use of this solvent.
Comply with all local air pollution regulations.
CAUTION: Perform a final wipe of the contacts with Isopropyl Alcohol, TT-I-735, or the contacts will not function electrically.
(b) Wipe sliding contacts, cams, and contact points of open switches with a clean cloth, cotton swabs, or pipe cleaners (as applicable), dampened with an approved solvent or Dry Cleaning Solvent, MIL-PRF-680, Type II, to remove Corrosion Preventive Compounds. Perform a final cleaning wipe with a clean cloth, cotton swabs, or pipe cleaners, as applicable, dampened with Isopropyl Alcohol, TT-I-735.
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h. Edge Connectors and Mating Plugs. Edge connectors on PCBs pose a particular corrosion problem because of the thinly plated surfaces. Most plugs and connectors used in microminiature circuit boards are plated with thin layers of gold. This gold is porous, and moisture will penetrate to the base metal, causing corrosion. In addition, the very function of cleaning may create scratches in the plated surfaces which will accelerate the problem. Remove corrosion and preserve as follows:
(1) Remove corrosion and tarnish by rubbing the affected area with a pencil eraser.
Care should be taken not to remove thinly plated surfaces.
NOTE: Local air pollution regulations may restrict the use of this solvent.
Comply with all local air pollution regulations.
(2) Clean the contact areas with an approved solvent or Dry Cleaning Solvent, MIL-PRF-680, using an acid brush. Rinse the affected area with Isopropyl Alcohol, TT-I-735, and wipe with a clean cloth or cheesecloth. Allow the component to air dry.
(3) Edge connectors should be preserved as follows:
(a) Spray a thin coating of Water-Displacing Corrosion Preventive Compound on both male and female sections of the connector, conforming to MIL-PRF-81309, Type III.
(b) Wipe off excess preservative with a clean cloth or cheesecloth.
i. Wet-Slug Tantalum Capacitors. Wet-slug tantalum capacitors can be internally damaged in service or during repair by the application of a reverse voltage. Such damage will often result in acid leakage which may cause corrosion in areas adjacent to the damaged capacitor. Capacitors having evidence of leakage should be replaced and all adjacent areas cleaned to prevent further corrosion. The following procedures should apply for the inspection of wet-slug tantalum capacitors:
(1) Inspect the seam between the slug and the case of each tantalum capacitor for evidence of small deposits of silver. The color of the silver deposit may be black or gray. When silver deposits are discovered, determine which capacitor is leaking, and then place one drop of the following solution on the suspected capacitor at the seam between the slug and the case and on the silver deposit.
(a) Dissolve 1/4 teaspoon of Thymol Blue Reagent indicator crystals in 3 cups (24 ounces) of deionized or distilled water, conforming to A-A-59282.
NOTE: Verify the color of the Thymol Blue Reagent indicator solution on a piece of white paper prior to use. The color of the solution should be amber or blue. If a reddish-purple color is indicated, the solution is contaminated and should be disposed of properly.
(b) Add 8 drops of ammonium hydroxide, conforming to O-A-451, to the Thymol Blue Reagent indicator and water solution. The ammonium hydroxide will aid in dissolving the Thymol Blue Reagent indicator crystals.
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(2) If no color change is observed at the wet-slug tantalum capacitor, remove the indicator solution and any residue with Isopropyl Alcohol, TT-I-735, and an acid brush or a dampened clean cloth. Dry and preserve in accordance with subparagraphs 603i(5) and (7).
(3) If an acid leak has occurred from a wet-slug tantalum capacitor, the solution will change from an amber or blue color to a reddish-purple color. Remove the damaged capacitor and neutralize the contaminated area by applying the following solution:
(a) Dissolve 8 ounces (1 cup) of sodium bicarbonate, conforming to O-S-576, in 1 gallon of fresh water.
(b) Apply the sodium bicarbonate solution to the affected area using an acid brush.
(c) Thoroughly rinse the affected area with deionized or distilled water. Ensure that the rinse water does not contaminate other areas.
(d) Apply another drop of the Thymol Blue Reagent indicator solution to the affected area. Inspect for the reddish-purple color. Repeat steps (b) and (c) above until no color change occurs.
(4) Clean the affected area by scrubbing with a nonabrasive pad. Thoroughly rinse the area with Isopropyl Alcohol, TT-I-735. Wipe the area with a clean cloth or cheesecloth.
(5) Air dry the component.
(6) Install the replacement capacitor.
(7) Preserve the area as follows:
(a) Spray a thin coating of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type III, on the capacitor and affected area.
(b) Wipe off excess preservative with a clean cloth or cheesecloth.
(8) Replace the conformal coating in accordance with the OEM’s maintenance instructions or Chapter 5, subparagraph 505e.
j. Aluminum Electrolytic Capacitors. Aluminum electrolytic capacitors that utilize synthetic rubber seals or rubber/plastic combination seals are susceptible to damage from cleaning solutions and processes. Such damage will often result in an acid leak which may cause corrosion in areas adjacent to the damaged capacitor. Capacitors having evidence of leakage should be replaced and all adjacent areas cleaned to prevent further corrosion. The following procedures should apply for the inspection and replacement of aluminum electrolytic capacitors:
(1) Inspect the end seals for deterioration. If the seal looks bulged or uneven, the capacitor should be replaced and all adjacent areas cleaned.
Par 603 Page 139
(2) Clean the affected area by scrubbing with a nonabrasive pad. Thoroughly rinse the area with Isopropyl Alcohol, TT-I-735. Wipe the area with a clean cloth or cheesecloth.
(3) Air dry the component.
(4) Install the replacement capacitor.
(5) Preserve the area as follows:
(a) Spray a thin coating of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type III, on the capacitor and affected area.
(b) Wipe off excess preservative with a clean cloth or cheesecloth.
(6) Replace the conformal coating in accordance with the OEM’s maintenance instructions or Chapter 5, subparagraph 505e.
k. Multipin Electrical Connectors Cleaning and Preservation.
(1) General. Multipin electrical connectors require special attention to prevent corrosion and electrical failures, especially when the connectors are in areas that are exposed to harsh environments. The following techniques and associated warnings, cautions, and notes will assist in limiting the corrosion attack.
WARNING: Ensure that all electrical and hydraulic power is removed from the aircraft or component. Install the applicable safety devices. Disconnect all batteries.
CAUTION: Cleaning compounds and solvents identified in Chapter 4 and Appendix 1 may react with some encapsulants or plastics used to form wire harness tubing, wire coatings, conformal coating, gaskets, seals, etc. Test on a small area for softening or other adverse reaction prior to general application. See Chapter 4, Table 4-3 for further restrictions on these materials.
NOTE: Local air pollution regulations may restrict the use of these solvents.
Comply with all local air pollution regulations. A continuity test does not preclude a visual inspection of connectors, because corrosion can still occur outside of pin areas.
(a) Protect open connectors with conductive plastic or metal caps.
Pressure-sensitive tape, conforming to MIL-T-22085, Type II, and as specified in Chapter 4, subparagraph 409e, is an alternate method of sealing connectors if proper caps are not available.
Par 603 Page 140 FIGURE 6-14. MULTIPIN CONNECTOR WITH “DOG BONES” INSTALLED (
b) If connector boots are installed and water intrusion cannot be prevented due to design, a small drain hole (1/4 inch minimum, 3/8 inch maximum) may be incorporated at the lowest point on the connector boot to allow water to drain. This action requires approval of the OEM.
(c) Special attention should be given to connectors using replaceable pins. These connectors use a self-sealing gasket that seals the connector against water intrusion. “Dog bones” (plastic inserts) are used to fill unused connector (pin) cavities. Figure 6-14 shows “dog bones” installed in a multipin connector. The self-sealing gasket may lose its effectiveness to seal against water intrusion with repeated removal and replacement of connector pins or omission of the “dog bones.” The use of potting compounds mentioned in Chapter 5, subparagraph 505b may be required to prevent water intrusion in extreme cases where the connector cannot be replaced.
(d) Connectors that are susceptible to the same environment as the aircraft wire harness connectors should be treated with the same corrosion removal and preservation techniques. Mounting plates normally contain a gasket that acts as a watertight seal. These gaskets should be inspected each time a connector is dismantled for cleaning or repair.
(2) External Corrosion Inspection, Removal, and Cleaning. Inspection, removal, and cleaning of corrosion on the exterior of electrical connectors (see Figures 6-15 and 6-16) should be performed as follows:
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(a) Disassemble the connector backshell, if possible, and visually inspect all parts for evidence of corrosion. Extensive corrosion damage may require the replacement of the connector.
(b) Remove corrosion by scrubbing with a nonabrasive pad or an abrasive nylon mat, conforming to A-A-58054, Type I, as appropriate. Ensure connector mating surface threads, shell, and mounting plate (if used) are cleaned.
(c) Wipe off residue with a clean cloth or cheesecloth.
(d) Apply Isopropyl Alcohol, TT-I-735, with a typewriter brush or toothbrush.
Scrub connector mating areas, threads, shell, and mounting plates.
(e) Remove solvent and residue with a clean cloth or cheesecloth. Allow all parts to air dry.
FIGURE 6-15. EXTERNAL MULTIPIN CONNECTOR CORROSION
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(3) Internal Corrosion Inspection, Removal, and Cleaning. Inspection, removal, and cleaning of corrosion on the interior of electrical connectors should be as follows:
NOTE: On most connectors it is difficult to clean and remove corrosion from the receptacle (female) contacts. If corrosion is noted, the most practical solution is to replace the pin.
(a) Visually inspect all areas of the connector for evidence of corrosion. Extensive corrosion damage may require the replacement of the pin(s) or the connector.
(b) Clean internal areas of the connector, wiring, and pins with Isopropyl Alcohol, TT-I-735, and an acid brush.
(c) Wipe excess solvent and residue with a clean cloth or cheesecloth. Use a pipe cleaner, as required, to remove solvent from the pin area.
FIGURE 6-16. EXTERNAL MULTIPIN CONNECTOR CORROSION
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(4) Sealing Connector Backshell. Moisture intrusion into a connector often occurs by way of the backshell. This problem is particularly acute after damage to the seal occurs during pin replacement. The backshell may be sealed as follows:
(a) Verify that sealing plugs (“dog bones”) are installed in unused contact cavities.
(b) Remove the retainer ring and Mylar tape (if present) from the back of the electrical connector. Slide the backshell and retainer ring in back of the electrical connector up the electrical wire bundle (see Figure 6-17).
(c) Tie back shielded wire pigtails, where applicable.
(d) Apply RTV sealing compound, conforming to MIL-A-46146, by inserting the sealant applicator nozzle approximately halfway into the wire bundle at the back of the connector (see Figure 6-17). Inject RTV sealing compound by squeezing the applicator tube while slowly withdrawing the nozzle from the wire bundle at the back of the connector. Repeat as many times as necessary at different locations around the connector to achieve a sealing compound thickness of 1/16 inch across the entire rear face of the connector. Position the connector in the vertical position until the sealing compound sets. The sealing compound will self-level in approximately 15 minutes.
FIGURE 6-17. CONNECTOR SEALING PROCEDURE Procedures:
1. Remove retainer ring.
2. Remove Mylar tape.
3. Peel back the shielded pigtails.
4. Remove the backshell to expose wiring.
5. Seal between wires.
Par 603 Page 144 NOTE: For those connectors exposed to fluids (dielectric, coolant, turbine oil, etc.) that adversely affect RTV sealant, conforming to MIL-A-46146, apply Sealing Compound, Synthetic Rubber, Accelerated, conforming to MIL-PRF-8516, to the connector backshell and wire bundle where temperatures will not exceed 250 °F (121 °C).
(e) After the connector has self-leveled for the required time, visually inspect the rear of the connector to ensure a complete seal. If areas are void of sealing compound, add additional sealing compound to entirely seal the back of the connector. The maximum depth of the sealing compound should not exceed 1/8 inch. The connector should be kept in the vertical position for a minimum of 30 minutes as the sealing compound cures to the tack-free condition.
After the initial 30-minute curing time, the connector may be moved around as required. Curing of the sealing compound will continue for approximately 24 hours.
(f) If a subsequent repair action requires the replacement of a contact (pin), inject a small amount of sealing compound around the replacement contact to restore the watertight seal.
Position the electrical connector in the vertical position for 30 minutes to allow the sealing compound to self-level and cure to a stable condition.
(g) Connectors that are exposed to severe environmental conditions, such as externally mounted connectors and those in wheel wells, bilges, etc., should be taped using an electrical insulating tape. After wrapping the connector and wire bundle with electrical tape, RTV sealing compound, conforming to MIL-A-46146, should be brushed over the tape.
(5) Water-Displacement and Treatment. After corrosion removal and cleaning, or any time connectors, plugs, or receptacles are disconnected for maintenance, treat as follows:
(a) Apply Isopropyl Alcohol, TT-I-735, liberally to internal and external sections of male and female connectors using an acid brush. Mate and unmate connectors several times to clean. Thoroughly rinse the connector with Isopropyl Alcohol, TT-I-735. Shake out excess solvent and wipe the connector with a clean cloth or cheesecloth. Allow the connector to air dry.
(b) Spray a thin coating of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type III, on the internal sections of the connectors, plugs, and receptacles. Avoid excessive application or overspray of preservative.
(c) If possible, tilt or rotate the connector down and around to drain excess preservative. Wipe off any additional preservative with a clean cloth or cheesecloth.
(d) Prior to connecting the threaded sections of the connector, plug, or receptacle backshell, treat threaded areas with Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type III.
(e) Mate connector sections. Wipe off excessive preservative with a clean cloth or cheesecloth.
(f) Apply a film of Water-Displacing Corrosion Preventive Compound, conforming to MIL-DTL-85054, to the exterior surfaces of connector plugs and receptacles.