Par 905 Page 177 FIGURE 9-1. TYPICAL ESD WORKSTATION
1. Wrist Strap with Resistor
2. Heel Straps/Grounders
3. Static-Dissipative Work Surface
4. Ionizer/Monitor
5. Bench
6. Ground Cords
7. Lined Antistatic Tote with Cover
8. Materials Drawers Labels, Pouches, Bags, Accessories
9. ESD- Protective Roll Materials
10. Static-Dissipative Floor Mat *Special chairs/stools and garments are not shown.
b. Packaging. Circuit cards and components should be packaged in ESD-protective packaging prior to leaving the ESD workstation. Static shielding bags which have a static-dissipative inner layer and a conductive outer layer are used for this purpose. They should be noncorrosive and should zip-lock or heat seal closed. All static shielding bags are identified with an ESD caution sticker over the closed seals, so that broken stickers will become indicators of opened bags. Figure 9-2 shows typical ESD caution labels. Cushion wrap (bubble wrap) used
Par 905 Page 178 around circuit cards should also be made of static-dissipative material. Circuit cards may be packaged in reusable ESD fast pack containers. At the equipment level, conductive connector receptacle dust caps are used to prevent ESD from entering the equipment through the connector receptacle and damaging sensitive components. In cases where conductive dust caps are unavailable, a conductive grid tape may be used to cover connector receptacles.
c. ESD Protection Guidelines. Procedures to prevent ESD damage should start at the time electronic equipment is removed from the aircraft and continue through the packaging, shipping, inspection, repair, testing, storage, and eventual reinstallation to the aircraft.
(1) When removing ESD-sensitive equipment from the aircraft, the aircraft should be grounded and power removed. Prior to disconnecting the cables from the equipment, personnel should touch the metal case of the equipment to equalize any electrostatic potentials. Once the cables are disconnected, conductive dust caps or conductive grid tape should be placed on the connector receptacles. The conductive dust caps or grid tape should not be removed until the equipment is at an ESD workstation or test station where ESD protection is in place. When installing ESD-sensitive equipment on the aircraft, the outer shell of the cable connector should be touched to the outer shell of the equipment mating connector to equalize electrostatic potentials. ESD-sensitive equipment should not be opened to expose circuit cards anywhere other than an ESD workstation.
(2) Testing and repair of ESD-sensitive circuit cards and equipment at an ESD workstation should include the following ESD protection procedures:
(a) Ensure work areas, equipment, and wrist strap assembly are grounded.
(b) Attach wrist strap and place metal tools and accessories on grounded bench surface.
(c) Place conductive container on bench. Remove components and circuit cards from ESD protective packaging by unzipping or heating to open. Remove shorting device if present. Avoid touching leads on components. Place components and circuit cards on conductive work surface/test fixture.
(d) Compressed gases will not be used to cool fixtures.
(e) Test through connectors or tabs only.
(f) After testing, replace shorting packages and protective packaging.
(g) Only high input impedance multimeters and test instruments should be used (to avoid sharp current transients).
(h) Dielectric strength tests are prohibited.
Par 905 Page 179 FIGURE 9-2. TYPICAL ESD CAUTION LABELS
(i) U se only static-dissipative type solvents.
(j) Heat guns for test or curing are prohibited.
(k) Drying lamps, photo spots, and thermal probes are allowed.
(l) Do not remove components or assemblies from their sockets with power applied.
(m) The use of air to clean equipment or circuit cards is prohibited unless a filtered ionizing air gun is used.
Par 905 Page 180
(n) Do not use a solvent ultrasonic cleaning bath for component assemblies.
(o) Cure conformal coating materials in accordance with OEM instructions either by normal ambient curing or in an oven that contains grounding provisions to prevent static charge buildup. Oven temperature adjustments should be precise and accurate to prevent needless eddy flow of coating during curing.
(p) Compressed carbon dioxide or nitrogen should not be used to cool the test chamber or oven without grounding provisions.
(3) ESD Packaging Guidelines. Correct packaging for shipment or storage of ESD-sensitive components and circuit card assemblies should be accomplished at the ESD workstation. A conductive tote may be used to carry ESD-sensitive components and assemblies from the repair workstation to the packaging workstation if required. At no time during shipment or storage should packaging identified by an ESD symbol be opened unless at an ESD workstation. ESD-sensitive equipment should be shipped or stored with conductive dust caps or conductive grid tape over connector receptacles.
(4) ESD Repair Personnel Guidelines. All personnel who repair, package or handle ESD-sensitive components, circuit card assemblies or equipment should have formal ESD training. The most extensive and costly ESD workstations will not provide protection if people are not properly trained in correct practices. Manufacturers and repair station facilities should require some type of ESD training certification for their personnel.
906. CORROSION CONTROL PRACTICES FOR ESD-SENSITIVE DEVICES.
a. General. Some types of ESD packaging can be corrosive and should be avoided. ESD dustcaps for connector receptacles made from carbon should be avoided due to corrosive tendencies. To identify these dustcaps, rub the dustcap on a piece of paper. If a mark is made on the paper, the dustcap contains carbon and should not be used.
b. Corrosion Inspection and Repair. Corrosion inspection and repair of circuit card assemblies and ESD-sensitive equipment should be conducted at an ESD workstation where proper ESD precautions may be taken. Corrective action depends on the size, the degree, and type of corrosion, in the damaged area. Maintenance personnel should refer to the applicable Original Equipment Manufacturer’s (OEM) service directives for specific repair procedures or the treatment of specific avionics equipment identified in Chapters 6 and 8.
907 through 1000. RESERVED.
Par 1001 Page 181 CHAPTER 10. EMERGENCY ACTION FOR SERIOUS CORROSION OF AVIONICS
EQUIPMENT 1001. GENERAL.
a. This chapter describes emergency corrosion cleaning and treatment procedures to be followed after aircraft or equipment accidents and incidents, particularly those involving exposure to large amounts of saltwater, fire extinguishing agents, industrial pollutants, soot, etc.
Immediate action must be taken to remove, clean, dry, and preserve all affected avionics equipment to reduce corrosion damage. When removal of avionics equipment is impractical, in-place cleaning, drying, and preserving should be accomplished.
b. The emergency action procedures outlined in the beginning of this chapter are normally used by the operator only to prevent further corrosion damage. Equipment that has received initial emergency treatment should be forwarded to an avionics repair station for cleaning, drying, inspection, operational checks, and preservation, or returned to the Original Equipment Manufacturer (OEM) for disposition as described later in this chapter.
1002. EMERGENCY RECLAMATION TEAM.
NOTE: In cases involving aircraft accidents, permission to remove equipment must be obtained from the senior Department of Transportation (DOT) member of the accident investigation team prior to the start of emergency reclamation procedures.
a. Goal of an Emergency Reclamation Team. Each organization that operates, stores, maintains, or repairs avionics equipment should have a team identified to handle emergency reclamation situations. The primary goal of the emergency reclamation team is to accomplish those tasks that are necessary to salvage the affected equipment and perform appropriate corrosion control efforts to minimize damage.
b. Emergency Reclamation Team Organization. An emergency reclamation team should consist of a senior team member whose responsibilities include directing the salvage, removal priority, and corrosion control efforts for the equipment involved. The size and composition of the remainder of the emergency reclamation team will depend upon the urgency of the situation, type of reclamation effort, and the size of the reclamation task.
1003. EMERGENCY PREPARATIONS.
a. Removal Priority. Each organization that operates, stores, maintains, or repairs avionics equipment should publish an instruction that defines the role and purpose of the emergency reclamation team. The instruction should provide general guidelines for the team to accomplish their task in a safe and efficient manner. It should be reviewed by the emergency reclamation team members on a regular basis, and should include a priority list for the removal and reclamation of equipment and a list of all anticipated tools and materials necessary to accomplish the reclamation task. Table 10-1 provides a recommended guide for a priority removal list.
Par 1003 Page 182 TABLE 10-1. PRIORITY GUIDE FOR EMERGENCY REMOVAL OF AVIONICS
EQUIPMENT Priority Type Equipment
1. Avionics Equipment (radios, computers, radar equipment, etc.)
2. Instruments (aircraft instruments, meters, etc.)
3. Electrical Equipment (switches, wiring, indicator light panels, etc.)
4. Miscellaneous Equipment (mounting racks, etc.)
b. Required Tools, Materials, and Equipment. Immediate availability of the necessary corrosion control tools, materials, and equipment will help to significantly reduce additional damage to the affected equipment. In addition to the corrosion control products listed in Appendix 1, other special support equipment that will be useful and should be readily available are:
(1) Dry nitrogen source,
(2) Dry air source,
(3) Vented drying oven (forced air),
(4) Vented drying oven (bulb-type),
(5) Hot air blowers,
(6) Pump, backpack-style, and
(7) Clean empty 55-gallon drums (removable lid).
c. Production Planning. Whenever possible, all salvaged components of the aircraft or equipment should be treated simultaneously. The most experienced personnel on the emergency reclamation team should be assigned to disassemble and process the affected equipment. This effort will reduce the corrosion potential and other damage to the equipment and ensure that the work is accomplished in a thorough and competent manner. Whenever possible, personnel that normally examine and evaluate this type of equipment should work closely with the disassembly and preservation personnel. This enables non-reclaimable items to be scrapped immediately and only usable components that were exposed to corrosive agents to be disassembled and treated.
The time saved by this procedure may be used in preserving salvageable components.
1004. EMERGENCY CLEANING PROCEDURES.
CAUTION: Cleaning compounds and solvents identified in Appendix 1 may react with some encapsulants or plastics used to form wire harness tubing, wire coatings, conformal coatings, gaskets, seals, etc. Test these compounds and solvents on a small area for softening or other adverse reactions prior to
Par 1004 Page 183 general application. See Chapter 4, Table 4-3, for further restrictions on these materials.
a. General. Where possible, the primary method of emergency cleaning described in subparagraph 1004b should be used. When a sufficient quantity of fresh water is not available, use one of the alternate emergency cleaning methods described in subparagraphs 1004c(1) through (3).
b. Primary Method. The primary method for the removal of saltwater, fire extinguishing agents, etc., should be used when a sufficient quantity of fresh water is available. The primary method procedures are:
(1) Flush all internal and external areas with clean fresh water. Whenever possible, units or subcomponents that have been removed should be immersed and flushed thoroughly in clean fresh water. A 55-gallon drum may be used for this purpose. Tilt the unit or subcomponent back and forth to aid in draining off the excess water.
(2) Blow off excess water with not more than 10 pounds per square inch (psi) air pressure or dry nitrogen. Deflect jet of air off interior, back, and sides of enclosure to diffuse.
(3) If there is any evidence of salt or fire extinguishing agents, a second cleaning action should be initiated using a solution of 1 part Aircraft Cleaning Compound to 10 parts of fresh water, conforming to MIL-PRF-85570, Type II. Scrub the affected areas with the cleaning solution using a brush. Flush thoroughly with fresh water and drain excess. The equipment may be immersed in fresh water to aid in removing hidden contaminants. Tilt the unit or equipment back and forth to aid in draining off the excess water.
(4) Blow off excess water as specified in subparagraph 1004b(2).
c. Alternate Methods. The following describes alternate cleaning methods when sufficient fresh water is not available.
(1) Solvent Method.
NOTE: Local air pollution regulations may restrict the use of this and other solvents. Comply with all local air pollution regulations.
(a) Clean exterior of equipment using a brush and dry cleaning solvent, MIL-PRF-680, Type II.
(b) Collect waste solvent from exterior cleaning and dispose of by recycling or as a hazardous waste.
CAUTION: Properly dispose of all hazardous waste in accordance with local regulations.
(c) Disassemble equipment as required. Clean and dry interior surfaces in accordance with instructions of subparagraphs 1004b(3) and (4).
Par 1004 Page 184
(2) Aircraft Cleaning Compound Method.
(a) Apply a solution of 1 part Aircraft Cleaning Compound to 9 parts of fresh water, conforming to MIL-PRF-85570, Type I. Scrub or wipe interior and exterior surfaces of equipment using a brush or clean cloth until contaminants become intermixed or emulsified.
Wipe off all surfaces thoroughly with a clean cloth removing contaminants and cleaner.
(b) Blow off excess solution with not more than 10 psi dry air pressure or dry nitrogen. Deflect the jet of air off interior, back, and sides of enclosure to diffuse.
(3) Water-Displacing Method. The water-displacing method should be used as the last choice of the alternate cleaning methods. Additionally, the water-displacing method is considered only temporary preservation until proper cleaning methods can be accomplished.
After application of the water-displacing compound, tag equipment with an appropriate marking indicating the component has been temporarily preserved with Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type II, but still requires cleaning.
(a) Blow off excess water and other contaminants from component with not more than 10 psi dry air pressure or dry nitrogen. Deflect the jet of air off interior, back, and sides of enclosure to diffuse.
(b) Totally immerse equipment in a 55-gallon drum of Water-Displacing Corrosion Preventive Compound, conforming to MIL-PRF-81309, Type II. Tilt the unit or equipment back and forth to aid in removing any water. Immerse the equipment a second time, repeating the tilting to thoroughly coat all surfaces. If total immersion is not practical, spray, brush, or wipe the interior and exterior of equipment with Water-Displacing Corrosion Preventive Compound.
(c) Blow off excess Water-Displacing Corrosion Preventive Compound from component with not more than 10 psi dry air pressure or dry nitrogen. Deflect the jet of air off interior, back, and sides of enclosure to diffuse.
1005. EMERGENCY DRYING AND PRESERVATION.
a. General. Drying and preservation are essential to eliminate any traces of water and to control corrosion until the equipment can be disassembled, inspected, and repaired at an authorized repair station.
b. Drying and Preservation Procedures. The following drying and preservation procedures should be used with the listed drying equipment after cleaning in accordance with subparagraph 1004b.
(1) Vented Drying Oven (Forced Air).
(a) Blow off excess liquid from component with not more than 10 psi dry air pressure or dry nitrogen. Deflect the jet of air off interior, back, and sides of enclosure to diffuse.
(b) Dry the equipment in a vented forced air oven at a temperature of not more than 130 °F (54 °C) for 1 to 2 hours.
Par 1005 Page 185
(c) For all avionics components and electrical connectors, apply (by spraying) a coating of Water-Displacing Corrosion Preventive Compound, Ultra-Thin Film, conforming to MIL-PRF-81309, Type III.
(2) Vacuum Oven Drying.
(a) Blow off excess liquid from component with not more than 10 psi dry air pressure or dry nitrogen. Deflect the jet of air off interior, back, and sides of enclosure to diffuse.
(b) Dry the equipment in a vacuum oven with a temperature of not more than 130 °F (54 °C) and a minimum pressure of 25 inches of Hg (inHg) for 1 to 2 hours.
(c) For all avionics components and electrical connectors, apply (by spraying) a coating of Water-Displacing Corrosion Preventive Compound, Ultra-Thin Film, conforming to MIL-PRF-81309, Type III.
(3) Vented Drying Oven (Bulb-Type).
(a) Blow off excess liquid from component with not more than 10 psi dry air pressure or dry nitrogen. Deflect the jet of air off interior, back, and sides of enclosure to diffuse.
(b) Dry the equipment in a vented bulb-type drying oven at not more than 130 °F (54 °C) for 4 to 6 hours.
(c) For all avionics components and electrical connectors, apply (by spraying) a coating of Water-Displacing Corrosion Preventive Compound, Ultra-Thin Film, conforming to MIL-PRF-81309, Type III.
(4) Hot Air Blower.
(a) Blow off excess liquid from component with not more than 10 psi dry air pressure or dry nitrogen. Deflect the jet of air off interior, back, and sides of enclosure to diffuse.
(b) Dry the equipment with a hot air blower until dry.
(c) For all avionics components and electrical connectors, apply (by spraying) a coating of Water-Displacing Corrosion Preventive Compound, Ultra-Thin Film, conforming to MIL-PRF-81309, Type III.
(5) Heated Compartment.
(a) Blow off excess liquid from component with not more than 10 psi dry air pressure or dry nitrogen. Deflect the jet of air off interior, back, and sides of enclosure to diffuse.
(b) Dry the equipment in a heated compartment with proper air circulation at a temperature between 100 °F (38 °C) and 130 °F (54 °C) until dry.
Par 1005 Page 186
(c) For all avionics components and electrical connectors, apply (by spraying) a coating of Water-Displacing Corrosion Preventive Compound, Ultra-Thin Film, conforming to MIL-PRF-81309, Type III.
1006. OPERATOR LEVEL EMERGENCY CLEANING PROCEDURES.
WARNING: Ensure that all electrical power internal and external to the aircraft or equipment is disconnected. Disconnect all batteries. Ensure that all safety devices are installed.
a. Removable Avionics Equipment. Equipment or components that are removed at the operator’s facility should be inspected for smoke, heat, fire damage, or damaged seals.
Equipment and components that are forwarded to the operator’s facility should have their background researched to determine the extent, cause of damage, and previous cleaning and preservation procedures that may have been accomplished. Most avionics equipment contain dissimilar metals and particular attention should be paid to these areas for evidence of corrosion during the inspection. If contaminated avionics equipment can be forwarded immediately and inducted into an avionics repair station for expeditious cleaning, inspection, and repair of damage, then the drying and preservation identified in paragraph 1005 is not necessary. When immediate induction into the avionics repair station is not possible, proceed with the drying and preservation procedures of paragraph 1005. When the aircraft or equipment has been exposed to saltwater intrusion, fire extinguishing agents, or water immersion, the aircraft or equipment should be cleaned, dried, and preserved as follows:
(1) Electrically ground the aircraft or equipment.
WARNING: Ensure that all electrical power sources, including batteries, are disconnected from the aircraft or equipment and all other powered systems (hydraulic, pneumatic, and mechanical) are deactivated.
(2) Ensure all external electrical power and batteries are disconnected. Remove hydraulic and pneumatic power and install safety struts in hydraulic, pneumatic, and mechanic actuated devices.
(3) Remove installed avionics equipment. Removal priority should be determined from the developed priority list for emergency reclamation of equipment or as directed by the emergency reclamation team leader. See paragraph 1003 and Table 10-1.
(4) Remove all covers, modules, and components authorized at this level.
(5) Tilt the equipment back and forth to allow accumulated water or other liquids to drain off.
(6) Examine the individual items thoroughly for evidence of saltwater, fire extinguishing agents, smoke, oily films, corrosion, etc.
(7) Items that are contaminated should be cleaned using the primary cleaning method described in subparagraph 1004b.
Par 1006 Page 187
(8) If the primary method cannot be performed for lack of available fresh water, use one of the alternate cleaning methods described in subparagraph 1004c.
(9) Tag all components, identifying date, cleaning and drying method, and type of preservation applied.
b. Removal and Cleaning of Identification and Modification Plates. Identification and modification plates can trap contaminants, allowing corrosion to start. The following procedures are applicable for the cleaning of identification and modification plates:
(1) Visually examine for the presence and the condition of a fillet seal along the edge of the identification and modification plates. Identification and modification plates with sealed edges that appear intact and undamaged do not have to be removed at this maintenance level.
Identification and modification plates with missing or damaged edge seals should be removed.
(2) Remove the affected identification and modification plate as required.
(3) Thoroughly clean both sides of the identification and modification plate and the adjacent mounting areas on the equipment using the primary cleaning method described in subparagraph 1004b.
(4) Installation of the identification and modification plates will depend on any additional processing of the avionics component at another level of maintenance. To maintain correct identity and configuration control, reinstall the identification and modification plates. If the avionics component will be repaired at the operator level and returned to service, proceed as follows:
(a) Visually examine the identification and modification plate and the adjacent mounting areas for evidence of corrosion. Clean, treat, and reapply any protective finish in accordance with Chapter 4, paragraph 405, and Chapter 5, paragraphs 502, 503, and 504, as required.
(b) After cleaning and surface treatment, lightly coat the seal by applying a coating of Sealing Compound to the underside of the identification and modification plate and the adjacent mounting areas, conforming to SAE-AMS-S-8802. Install identification and modification plate within the working time of the sealant. Ensure sealant squeezes out around the periphery of the plate.
c. Hermetically Sealed Avionics Equipment. When removing hermetically sealed units, pay particular attention to cable clamp areas, bindings securing wire harnesses, and cable connectors. These are areas where salt and fire extinguishing agents can become entrapped.
Immerse the unit in a container of fresh water to test for airtight integrity of the seal. The presence of air bubbles will indicate a faulty seal. Clean hermetically sealed avionics equipment as follows:
Par 1006 Page 188
(1) Clean the equipment in accordance with subparagraph 1004b or c.
(2) Dry and preserve the equipment in accordance with one of the methods described in subparagraph 1005b.
(3) Units that indicate a faulty seal should be forwarded to an avionics repair station for disposition.
d. Electric Motors and Generators. Cleaning is an essential preliminary procedure in salvaging electric motors, generators, inverters, and miniature synchro transmitters and receivers.
(1) Clean the equipment in accordance with subparagraph 1004b or c.
(2) Dry and preserve the equipment in accordance with one of the methods described in subparagraph 1005b.
(3) Thoroughly inspect the equipment to determine whether it may be returned to serviceable condition or must be forwarded to an avionics repair station. Equipment with sealed bearings should be forwarded to an avionics repair station for replacement.
(4) Equipment that is determined serviceable should have the Corrosion Preventive Compound removed using Dry Cleaning Solvent, MIL-PRF-680, Type II.
(5) Blow off excess liquid from component with not more than 10 psi dry air pressure or dry nitrogen. Deflect the jet of air off interior, back and sides of enclosure to disuse.
e. Cockpit Area Components. The cockpit area contains various types of components.
Non-removable components and equipment should be cleaned, dried, and preserved in accordance with subparagraphs 1006i through 1006k. Removable components should be cleaned and preserved as follows:
(1) Remove all removable components, control boxes, equipment, relay boxes, indicators, etc., in accordance with the OEM maintenance instructions.
(2) Visually examine all removed components for evidence of saltwater, fire extinguishing agents, smoke, oily films, etc.
(3) Clean contaminated equipment in accordance with subparagraph 1004b.
(4) Dry and preserved the equipment in accordance with subparagraph 1005b.
(5) Special attention should be given to cockpit electrical connectors. Clean and preserve in accordance with subparagraph 1006m.
(6) Cockpit circuit breakers, toggle, rotary, interlock, and push-button switches should be cleaned and preserved in accordance with subparagraph 1006f.
f. Switches and Circuit Breakers. Most aircraft and aircraft-related test equipment switches are enclosed in a sealed case. Cleaning of internal parts is generally not possible.