• Cleaning agents
• De-icing fluids
• Paint
• Soft drinks
• Coffee
(3) Contaminants requiring special consideration.
(a) Special consideration is required for the following:
• Hydraulic fluids
• De-icing fluids
• Battery electrolyte
(b) These fluids, although essential for airplane operation, can damage EWIS components, such as connector grommets, wire bundle clamps, wire ties, and wire lacing, causing chafing and arcing. EWIS components exposed to these fluids should be given special attention during inspection. Contaminated wire insulation that has visible cracking or breaches to the core conductor can eventually arc and cause a fire. Wiring and other EWIS components exposed to, or in close proximity to, any of the above chemicals may need to be inspected more frequently for damage or degradation.
(c) When cleaning areas or zones of the airplane that contain both wiring and chemical contaminants, special cleaning procedures and precautions may be needed. Such procedures may include wrapping wire connectors and other EWIS components with a protective covering prior to cleaning. This would be especially true if pressure washing equipment is used.
In all cases, the airplane manufacturer’s recommended procedures should be followed.
(4) Waste system contamination. Waste system spills also require special attention.
Service history has shown that these spills can have detrimental effects on airplane EWIS and have resulted in smoke and fire events. When this type of contamination is found, all affected components in the EWIS should be thoroughly cleaned, inspected, and repaired, or replaced if necessary. The source of the spill or leakage should be located and corrected.
f. Heat. Exposure to high heat can accelerate degradation of EWIS by causing wire insulation dryness and cracking. Direct contact with a high heat source can quickly damage insulation. Burned, charred, or even melted insulation are the most likely indicators of this type of damage. Low levels of heat can also degrade wiring over a longer period of time. This type of degradation is sometimes seen on engines, in galley wiring such as in coffee makers and ovens, and behind fluorescent lights, especially ballasts.
g. Cold. Exposure to extremely cold temperatures, such as those found at a transport category airplane’s typical cruising altitude, or wires exposed to cold temperatures while the airplane is parked in a cold environment, increases the rigidity of wire insulation in those wires that have little or no current flow. Vibration or other types of movement of EWIS during this time could lead to wire faults. This is important to remember when performing maintenance to, or around, these wires in a cold environment. EWIS located outside of the pressurized fuselage, such as those located in landing gear wheel wells, wing leading and trailing edges, and in the horizontal and vertical stabilizers are routinely subjected to these extreme cold temperatures.
14. General EWIS Maintenance Guidance. Areas to be inspected should be clean enough to minimize the possibility that collected dirt, grease, or other contaminants might hide unsatisfactory conditions that would otherwise be detected during inspection. For any cleaning considered necessary, you should use the airplane manufacturer’s procedures or other methods, techniques, and practices acceptable to the FAA. The cleaning process itself should not compromise the integrity of EWIS.
a. Preventing Accumulation of Combustibles. Some applicants may set a numerical limit on the amount of contamination that may accumulate in a zone in order to avoid combustion of the contaminants. Other applicants may choose not to set a numerical limit, but rather give instructions that EWIS be cleaned to significantly remove the amount of combustible material.
If an applicant has set a limit, EWIS should be cleaned at frequent enough intervals that the accumulation of combustibles never exceeds this limit. If no limit has been set, EWIS should be cleaned at frequent enough intervals that accumulation of combustibles never reaches unacceptable levels. Determining the interval would involve making an estimate of the rate at which combustible material will accumulate in that particular zone and setting intervals to occur with enough frequency so that unacceptable levels are not reached. If at an inspection the contaminants in a zone have not yet accumulated to the level considered excessive, or to the set level that triggers the need for cleaning, a determination must be made about whether the contaminant accumulation will have exceeded the limit or reached excessive levels before the next inspection. If that is expected to be the case, then the EWIS should be cleaned during the current inspection even though the contaminants have not yet exceeded the accumulation limit or reached excessive levels.
b. Levels of Inspection Applicable to EWIS. Though the term “detailed visual inspection” remains valid for a detailed inspection using only eyesight, this may represent only part of the inspection called for in EWIS ICA used to establish an operator’s maintenance program. We recommend that the acronym “DVI” not be used because that term may exclude tactile examination, which is sometimes needed. Instead, we provide the following definitions.
See figures 1 and 2 for examples of EWIS that are contaminated. Such contamination could cause EWIS component degradation and also prevent an effective GVI or DET inspection if it were not cleaned. Additionally, depending on the type and amount present, contaminants may also be combustible and sustain a fire should electrical arcing occur.
Figure 1: EWIS Contaminated with Dust and Dirt
Figure 2: EWIS Contaminated with Grease
(1) Detailed inspection (DET). A DET is an intensive examination of a specific item, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at an intensity deemed appropriate.
Inspection aids such as mirrors, magnifying lenses, or other means may be necessary. Surface cleaning and elaborate access procedures may be required. A DET can be more than just a visual inspection, since it may include tactile assessment in which a component or assembly is checked for tightness/security. It may require the removal of items such as access panels and drip shields, or the moving of components.
Note: Tactile assessment as used in the context of an EWIS DET does not require the disassembly of wire bundles to inspect individual wires within the bundle.
(2) General visual inspection (GVI). A visual examination of an interior or exterior area, installation, or assembly to detect obvious damage, failure, or irregularity. This level of inspection is made from within touching distance unless otherwise specified. A mirror may be necessary to enhance visual access to all exposed surfaces in the inspection area. This level of inspection is made under normally available lighting conditions such as daylight, hangar lighting, flashlight, or droplight and may require removal or opening of access panels or doors. Stands, ladders, or platforms may be required to gain proximity to the area being checked.
(a) Recent changes to this definition have added proximity guidance (within touching distance) and the allowance of a mirror and flashlight to improve visual access to exposed surfaces when performing a GVI. These changes should result in more consistent application of the GVI. They also support expectations of the types of EWIS discrepancies that should be detected by a GVI.
(b) When performing a GVI, there is usually no need to remove equipment or displace EWIS unless the access instructions specifically call for it.
(c) The area to be inspected should be clean enough to minimize the possibility that collected dirt or grease, or other contaminants, might hide unsatisfactory conditions that would otherwise be obvious. For any cleaning considered necessary, you should use the airplane manufacturer’s procedures or other methods, techniques, and practices acceptable to the FAA.
The cleaning process itself should not compromise the integrity of EWIS. Avoid using high pressure cleaning and abrasive materials that could damage wire insulation and other EWIS components.
(d) In general, the person performing a GVI is expected to identify degradation from wear, vibration, moisture, contamination, excessive heat, aging, and so forth, and assess what actions are appropriate to address the discrepancy. This assessment should consider potential effects on adjacent system installations, particularly if those systems include wiring.
You should address any observed discrepancies, such as chafing, broken clamps, sagging, interference, contamination, and so forth.
(e) An EWIS stand-alone GVI applies the above inspection techniques to wires, cables, and other EWIS components identified in the inspection procedure.
(3) Zonal inspection. This is a collective term comprising selected GVIs and visual checks that are applied to each zone of the airplane, defined by access and area, to check system and powerplant installations and structure for security and general condition. A zonal inspection is essentially a GVI of an area or zone to detect obvious unsatisfactory conditions and 22
discrepancies. Unlike a stand-alone GVI, it is not directed to any specified component or assembly.
c. EWIS-Related Guidance for Zonal Inspections. The following EWIS degradation conditions are typical of what should be detectable and addressed as a result of a zonal inspection (as well as a stand-alone GVI). Maintenance and training documentation should include these items. This list is not intended to be all-inclusive and may be expanded as appropriate.
(1) Wire/wire harnesses.
• Wire bundle/wire bundle or wire bundle/structure contact/chafing
• Wire bundles sagging or improperly secured
• Wires damaged (obvious damage because of mechanical impact, overheat, localized chafing, and so forth)
• Lacing tape and/or ties missing/incorrectly installed
• Wiring protection sheath/conduit deformed or incorrectly installed
• End of sheath rubbing on end attachment device
• Grommet missing or damaged
• Dust and lint accumulation
• Surface contamination by metal shavings/swarf
• Contamination by liquids
• Deterioration of previous repairs (for example, splices)
• Deterioration of production splices
• Inappropriate repairs (for example, an incorrect splice)
• Inappropriate attachments to or separation from fluid lines
(2) Connectors.
• External corrosion on receptacles
• Backshell tail broken
• Rubber pad or packing on backshell missing
• No backshell wire securing device 23
• Foolproofing chain broken
• Safety wire missing or broken
• Discoloration/evidence of overheat on terminal lugs/blocks
• Torque stripe misaligned
(3) Switches.
• Rear protection cap damaged
• Missing hardware (screws, washers, and so forth)
• Loose hardware
• Improper hardware
(4) Ground points.
• Corrosion
• Loose hardware
(5) Bonding braid/bonding jumper.
• Braid broken or disconnected
• Multiple strands corroded
• Multiple strands broken
(6) Wiring clamps or brackets.
• Corroded
• Broken/missing
• Bent or twisted
• Unstuck/detached
• Attachment faulty (bad attachment or fastener missing)
• Protection/cushion damaged 24
(7) Supports (rails or tubes/conduit).
• Broken
• Deformed
• Fastener missing
• Edge protection on rims of feed-through holes missing
• Racetrack cushion damaged
• Drainage holes (in conduits) obstructed
(8) Circuit breakers, contactors, or relays.
• Signs of overheating
• Signs of arcing
• Missing hardware (screws, washers, and so forth)
• Loose hardware
• Improper hardware
d. Wiring Installations and Areas of Concern. Maintenance material should address the following installations and areas.
(1) Wiring installations.
(a) Clamping points. Damaged clamps, migration of clamp cushions, or improper clamp installations aggravate wire chafing. Airplane manufacturers specify clamp type and part number for EWIS throughout the airplane. When replacing clamps, use those specified by the airplane manufacturer. Tie wraps provide a rapid method of clamping, especially during line maintenance operations. But improperly installed tie wraps can have a detrimental effect on wire insulation. When new wiring is installed as part of an STC or other modification, the drawings will provide wire routing, clamp type and size, and proper location. Examples of significant wiring alterations are the installation of new avionics systems, new galley equipment, and new instrumentation. Wire routing, type of clamp, and clamping location should conform to the approved drawings. Adding new wire to existing wire bundles may overload clamps, causing wire bundles to sag and wires to chafe. Raceway clamp foam cushions may deteriorate with age, fall apart, and thus fail to provide proper clamping.
(b) Connectors. Worn environmental seals, loose connectors, missing seal plugs, missing dummy contacts, or lack of strain relief on connector grommets can compromise connector integrity and allow contamination to enter the connector, leading to corrosion or grommet degradation. Connector pin corrosion can cause overheating, arcing, and pin-to-pin 25
shorting. Drip loops should be maintained when connectors are below the level of the harness, and tight bends at connectors should be avoided or corrected.
(c) Terminations. Terminations, such as terminal lugs and terminal blocks, are susceptible to mechanical damage, corrosion, heat damage, and contamination from chemicals, dust, and dirt. Over time, vibration can cause high-current-carrying feeder cable terminal lugs to lose their original torque value, resulting in arcing. One sign of this is heat discoloration at the terminal end. Proper build-up and nut torque is especially critical on high-current-carrying feeder cable lugs. Corrosion on terminal lugs and blocks can cause high resistance and overheating. Dust, dirt, and other debris are combustible and could sustain a fire if ignited from an overheated or arcing terminal lug. Terminal blocks and terminal strips located in equipment power centers (EPC), avionics compartments, and throughout the airplane need to be kept clean and free of combustibles.
(d) Backshells. Wires may break at backshells from excessive flexing, lack of strain relief, or improper build-up. Loss of backshell bonding may also occur because of these and other factors.
(e) Sleeving and conduits. Damage to sleeving and conduits, if not corrected, may lead to wire damage. So damage such as cuts, dents, and creases on conduits may require further investigation for condition of wiring within.
(f) Grounding points. You should check grounding points for security (in other words, finger tightness), condition of the termination, presence of corrosion, and cleanliness.
Grounding points that are corroded or have lost their protective coating should be repaired.
(g) Splices. Both sealed and non-sealed splices are susceptible to vibration, mechanical damage, corrosion, heat damage, chemical contamination, and environmental deterioration. Power feeder cables normally carry high current levels and are very susceptible to installation error and splice degradation. All splices should conform to the TC or STC holder’s published recommendations. In the absence of published recommendations, we recommend use of environmentally sealed splices.
(2) Areas of concern.
(a) Wire raceways and bundles. Adding wires to existing wire raceways may cause undue wear and chafing of the wire installation and inability to maintain the wire in the raceway. Adding wire to existing bundles may cause wire to sag against the structure, which can cause chafing.
(b) Wings. Wing leading and trailing edges are difficult environments for wiring installations. On some airplane models, wing leading and trailing edge wiring is exposed whenever the flaps or slats are extended. Slat torque shafts and bleed air ducts in these areas are other potential damage sources.
(c) Engine, pylon, and nacelle area. These areas experience high vibration, heat, and frequent maintenance, and they are susceptible to chemical contamination.
(d) Accessory compartment and equipment bays. These areas typically contain items such as electrical components, pneumatic components and ducting, and hydraulic components and plumbing. They may be susceptible to vibration, heat, and liquid contamination.
(e) Auxiliary power unit (APU). Like the engine/nacelle area, the APU is susceptible to high vibration, heat, frequent maintenance, and chemical contamination.
(f) Landing gear and wheel wells. This area is exposed to severe external environmental conditions in addition to vibration and chemical contamination.
(g) Electrical panels and line replaceable units (LRUs). Electrical panel wiring is particularly prone to broken wires and damaged insulation when these high density areas are disturbed during troubleshooting activities, alterations, and refurbishments. Tying wiring to wooden dowels to reduce its disturbance during modification can minimize wire damage. For some configurations, use of connector support brackets would be more desirable and cause less wire disturbance than removal of individual connectors from the supports.
(h) Batteries. Wires and other EWIS components in the vicinity of all airplane batteries are susceptible to corrosion and discoloration and should be inspected for those problems. You should inspect discolored wires and other EWIS components for serviceability.
(i) Power feeders. High-current wiring and associated connections have the potential to generate intense heat. Vibration may cause degradation or loosening of power feeder cables, terminals, and splices. If signs of overheating are seen, splices or termination should be replaced. For both galley and engine/APU generator power feeders, depending on the design, service experience may indicate a need for periodic checks of proper torque on power feeder cable terminal ends, especially in high vibration areas.
(j) Under galleys, lavatories, and cockpit. Areas under the galleys, lavatories, and cockpit are particularly susceptible to contamination from such things as coffee, food, water, soft drinks, lavatory fluids, dust, and lint. Proper floor panel sealing procedures can minimize such contamination in these areas.
(k) Fluid drain plumbing. Leaks from fluid drain plumbing could lead to liquid contamination of EWIS. Service experience may show a need for periodic leak checks or cleaning, in addition to routine visual inspections.
(l) Fuselage drain provisions. Some installations include plumbing features designed to catch leakage and drain it to an appropriate exit. Blockage of the drain path can result in liquid contamination of EWIS. In addition to routine visual inspections, service experience may signal a need to check these installations and associated plumbing periodically to ensure the drain path is free of obstructions.
(m) Cargo bay underfloor. Damage to EWIS in the cargo bay underfloor can occur from maintenance activities in the area.
(n) EWIS subject to movement. Wiring and other EWIS components that are subject to movement or bending during normal operation or maintenance access, at locations such as doors, actuators, landing gear mechanisms, and electrical access panels, should be inspected at those areas where movement occurs.
(o) Access panels. EWIS near access panels could be accidentally damaged from repetitive maintenance access and may warrant special attention.
(p) Under doors. Areas under cargo, passenger, and service entry doors are susceptible to fluid entering from rain, snow, and liquid spills. Fluid drain provisions and floor panel sealing in these areas should be periodically inspected and repaired as necessary.
(q) Under cockpit sliding windows. Areas under cockpit sliding windows are susceptible to water entering from rain and snow. Fluid drain provisions in these areas should be periodically inspected and repaired as necessary.
(r) Areas where EWIS is difficult to access. Areas difficult to access, such as flight deck instrument panels and the cockpit pedestal area, could accumulate excessive dust and other contaminants because of infrequent cleaning. In these areas, it may be necessary to remove components and disassemble other systems to facilitate access to the area.
15. Protection and Caution Recommendations. Section 43.13(b) requires anyone performing maintenance or alteration to do the work “. . . in such a manner and use materials of such a quality that the condition of the aircraft, airframe, aircraft engine, propeller, or appliance worked on will be at least equal to its original or properly altered condition (with regard to aerodynamic function, structural strength, resistance to vibration and deterioration, and other qualities affecting airworthiness).” Anyone performing maintenance must use methods, techniques, and practices prescribed in the manufacturer’s current maintenance manual or in ICA prepared by the manufacturer, or methods, techniques, and practices referred to in § 43.13(a) as acceptable to the FAA Administrator. Protection and caution recommendations, while not required as part of the EZAP process discussed in this AC, are required by paragraph H25.5(a)(1)(vi) of appendix H to part 25. They are an important part of the “protect and clean as you go” philosophy, which contributes to preserving the integrity of EWIS. Some practices in use today may actually compromise the integrity of EWIS, albeit inadvertently. Therefore, we have identified some specific maintenance and servicing tasks and recommend that air carriers and air operators adopt these more robust practices. Such information may be provided in manufacturer and operator training programs, on job/task cards, or any other documents that the manufacturer or operator use in the administration of their maintenance programs. These maintenance practices will help prevent inadvertent contamination of EWIS with harmful solids (such as metal shavings) or fluids during maintenance, alteration, and repair of airplane structures and components. Training of maintenance and servicing personnel should address potential consequences of their actions to wiring in the work area. AC 120-94, Aircraft Electrical Wiring Interconnection Systems Training Program, provides details of EWIS training that could be adopted by air carriers and air operators.
a. Installation, Repair, or Modification of EWIS. Wiring and other EWIS components (for example, protective coverings, connectors, clamping provisions, and conduits) often comprise the most vulnerable and maintenance-sensitive portions of an installation or system.
Extreme care and proper procedures should be used during installation, repair, or modification of EWIS components to ensure safe and reliable performance of the EWIS function.
(1) Proper EWIS component selection, routing/separation, clamping configurations, use of splices, repair or replacement of protective coverings, pinning/de-pinning of connections, and so forth, should be performed in accordance with the applicable sections of the AMM, SWPM/ESPM, or other manufacturer’s maintenance documents or in accordance with the operator’s approved maintenance program.
(2) You should take special care to minimize disturbance of existing adjacent wiring and other EWIS components during maintenance activities. When EWIS is displaced during a maintenance activity, special attention should be given to returning it to its normal configuration in accordance with the applicable maintenance instructions.
b. Structural Repairs and STCs. Structural repairs and STC installations inevitably introduce tooling and residual debris that is harmful to airplane wiring and other EWIS components. They often require displacement or removal of EWIS to provide access to the work area. Even minor displacement of wiring, especially while clamped, can damage its insulation and result in degraded performance, leading to subsequent arcing or circuit failure.
(1) Use extreme care to protect EWIS from mechanical damage by tools or other equipment during structural repairs, installation of STCs, and repairs or alterations. Avoid drilling blindly into the airplane structure. Damage to wire insulation could cause arcing, fire, and smoke. Carefully cover or displace EWIS located adjacent to drilling or riveting operations to reduce the possibility of mechanical damage.
(2) Do not allow debris such as drill shavings, liberated fastener pieces, broken drill bits, and so forth, to contaminate or penetrate wiring, other EWIS components, or electrical components. This can cause damage to insulation and potential arcing by providing a conductive path to ground or a conductive path between two or more wires of different loads. Once wire bundles and other EWIS components are contaminated with this type of debris, it is extremely difficult to remove it. So take precautions to prevent contamination of any kind from entering the wire bundle.
(3) Before beginning structural repair work and STC installation, survey the work area carefully to identify all EWIS and electrical components that may be subject to contamination.
EWIS and electrical components in the debris field should be covered or removed. Drills equipped with vacuum aspiration can be used to minimize risk of metallic debris contaminating wire bundles or other EWIS components. When work is completed, clean electrical components, wiring, and other EWIS components in accordance with the applicable maintenance instructions.
c. Airplane De-Icing or Anti-Icing. Exercise care when spraying de-/anti-icing fluids to prevent damage to exposed electrical components and EWIS in areas such as wing leading and 29
trailing edges, wheel wells, and landing gear. Direct pressure spray onto electrical and EWIS components can lead to contamination or degradation, and it should be avoided.
d. Inclement Weather. EWIS in areas below doorways, floors, access panels, and servicing bays are prone to corrosion or contamination from exposure to the elements. Snow, slush, or excessive moisture should be removed from these areas before closing doors or panels.
Before loading items into the airplane (for example, cargo containers), remove deposits of snow or slush. Keep doors/panels closed as much as possible during inclement weather to prevent ingress of snow, slush, or excessive moisture.
e. Component Removal/Installation (Relating to Attached EWIS).
(1) Excessive component handling and movement during installation and removal may harm EWIS. Use appropriate connector pliers (for example, soft jawed) to loosen coupling rings that are too tight to be loosened by hand. Alternately pull on the plug body and unscrew the coupling ring until the connector is separated. Do not use excessive force and do not pull on attached wires. When reconnecting, take special care to ensure the connector body is fully seated, the jam nut is fully secured, and no tension is on the wires.
(2) When equipment is disconnected, use protective caps on all connectors (plug or receptacle) to prevent contamination or damage of the contacts. Sleeves or plastic bags may be used if protective caps are not available. Use of sleeves or plastic bags should be temporary because of the risk of condensation. Use of a humidity absorber is recommended with sleeves or plastic bags.
f. Pressure Washing. Exercise care when spraying water or cleaning fluids to prevent damage to exposed electrical components and EWIS in areas such as wing leading and trailing edges, wheel wells, and landing gear. Avoid direct high-pressure spray onto electrical components and EWIS. It can lead to contamination or degradation. When practical, protect EWIS components (for example, wiring and connectors) before pressure washing. Use water rinse to remove cleaning solution residue after washing. Breakdown of wire insulation or material used in other EWIS components may occur with long-term exposure of EWIS components to cleaning solutions. Although these recommendations are good practice and technique, consult the AMM or STC holder’s instructions for additional detailed instructions about pressure washing.
g. Cleaning of EWIS (In Situ). Exercise extreme care and use proper procedures when cleaning to ensure safe and reliable performance of the function supplied by EWIS. Although these recommendations for cleaning of EWIS are considered good practice and technique, consult the AMM or STC holder’s instructions for additional detailed instructions.
(1) Avoid displacing or disturbing EWIS during cleaning of non-aggressive contamination, such as dust, dirt, or swarf. Displacement may be necessary for aggressive contaminants (for example, livestock waste, salt water, battery electrolyte). In those cases, release wiring from its installation in a way that avoids placing undue stress on the wiring connectors and wire bundle support devices. If liquid contamination enters the bundle, remove ties before separating wires.