Note: The MRB chairperson’s signature does not indicate approval of compliance with the requirements of §§ 26.11 and 25.1729. Those compliance findings must be issued by the FAA oversight office.
(i) The DAH prepares instructions for continued airworthiness, which include EZAP-derived EWIS ICA based upon the content of the approved MRBR.
(j) The DAH produces the SD (required by paragraph H25.5(b)), which either contains or identifies the location of the EWIS ICA. (The SD can either contain the EWIS ICA or reference its location in other documents—it is the DAH’s choice.)
(k) The DAH submits the SD and any referenced ICA documents to the FAA oversight office for approval.
(l) The FAA oversight office, in conjunction with the applicable AEG office, reviews and approves the SD, which indicates approval of the EWIS ICA referenced or contained in that document.
(2) Following are the typical steps that DAHs or applicants will need to go through in determining whether the design change for which they seek approval requires revisions to previously approved EWIS ICA or the development of new EWIS ICA, or both. A design change can be accomplished through an amended TC (including service bulletins describing design changes), an STC, or changes to an existing STC. These actions apply to applicants who must comply with § 25.1729 (in other words, paragraphs H25.5(a)(1) and (b) of appendix H) or § 26.11(c), or both.
Note: The steps below are focused on the development, review, and approval of the EZAP-derived EWIS ICA. Other EWIS ICA tasks and non-EWIS ICA may also be addressed during the review process, but, for clarity, they are purposely left out of the following sequence of events.
(a) The applicant determines whether the proposed design change requires a revision to the existing EWIS ICA or development of new EWIS ICA, or both. Guidance on making this determination is contained in appendix B of this AC. If required, the applicant develops a new or revised EWIS ICA.
(b) If new or revised EWIS ICA are required, the applicant produces a SD (required by paragraph H25.5(b)) containing the EWIS ICA (developed using the procedure outlined in appendix B of this AC) or identifying their location in other documents. (Whether the SD contains the EWIS ICA or references their location in other documents is the applicant’s choice).
(c) The DAH submits the SD, any referenced ICA documents, and any supporting documentation to the FAA oversight office for approval.
Note: Supporting documentation may be the result of the procedure as outlined in appendix B, previously approved EWIS ICA applicable to the airplane zone(s) 16
being modified, or other documentation that supports the applicant’s position as to the necessity of creating new or revised EWIS ICA.
(d) The FAA oversight office, in conjunction with the applicable AEG office, reviews and approves the SD, which indicates approval of the EWIS ICA referenced or contained in that document.
11. Making EWIS ICA Available to Operators and Other Persons. Section 26.11(e)(4) requires that the compliance plan submitted by the DAH or applicant contains a proposal for how the approved EWIS ICA will be made available to affected persons. Section 26.11(f) requires that the compliance plan be implemented in accordance with § 26.11(e). The rule does not specify the manner in which the DAH must make the EWIS ICA available. It simply requires the DAH to make them available. The “affected persons” that the rule refers to are operators and others required to comply with the requirements of §§ 26.11, 25.1729, 121.1111, and 129.111.
12. Operator Changes to EWIS ICA. Sections 121.1111 and 129.111 require that the EWIS maintenance program be based on EWIS ICA that have been developed in accordance with provisions of appendix H and approved by the FAA oversight office. Guidance for air carriers and air operators on how to make changes to FAA-approved EWIS ICA is contained in AC 120-99, Incorporation of Electrical Wiring Interconnection System (EWIS) Instructions for Continued Airworthiness into an Operator’s Maintenance Program.
13. Causes of Wire and Other EWIS Component Degradation. The following are considered principal causes of wiring degradation and should be used to help focus maintenance programs.
a. Vibration. High vibration areas tend to accelerate degradation over time, resulting in “chattering” contacts and intermittent symptoms. High vibration of tie-wraps or string-ties can cause damage to insulation. In addition, high vibration will exacerbate any existing wire insulation cracking.
b. Moisture. High moisture areas generally accelerate corrosion of terminals, pins, sockets, and conductors. It should be noted that wiring installed in clean, dry areas with moderate temperatures appears to hold up well.
c. Maintenance. Scheduled and unscheduled maintenance activities, if done improperly, may contribute to long-term problems and degradation of EWIS. Certain repairs may have limited durability and should be evaluated to ascertain if rework is necessary. Repairs that conform to manufacturers’ recommended maintenance practices are generally considered permanent and should not require rework. Care should be taken to prevent undue collateral damage to EWIS while performing maintenance on other systems.
(1) Metal shavings and debris have been discovered on wire bundles after maintenance, repairs, modifications, or STC work has been performed. Take care to protect wire bundles, connectors, and all other EWIS components during maintenance, repairs, or modification work.
Work areas should be cleaned while the work progresses to ensure that all shavings and debris are removed. The work area should be thoroughly cleaned after work is complete, and the area should be inspected after the final cleaning.
(2) Repairs should be performed using the most effective methods available. Since wire splices are more susceptible to degradation, arcing, and overheating, the recommended method of repairing a wire is with an environmentally sealed splice.
d. Indirect Damage. Events such as pneumatic duct ruptures or duct clamp leakage can cause damage that, while not initially evident, can later cause wiring problems. When events such as these occur, surrounding EWIS should be carefully inspected to ensure that there is no damage or potential for damage evident. Indirect damage caused by these types of events could be broken clamps or ties, broken wire insulation, or even broken conductor strands. In some cases, the pressure of the duct rupture could cause wire separation from the connector or terminal strip.
e. Contamination. EWIS contamination refers to either of the following situations:
(1) presence of a foreign material that is likely to cause degradation of EWIS or (2) presence of a foreign material that is combustible or capable of sustaining a fire after removal of the ignition source. An EWIS contaminant may be in solid or liquid form.
(1) Solid contaminants. Solid contaminants such as the following can accumulate on wiring and other EWIS components and could degrade or penetrate wiring or other EWIS components.
• Metal shavings/swarf
• Debris
• Livestock waste
• Lint
• Dust
(2) Fluid contaminants. Chemicals in fluids such as the following can contribute to degradation of wiring and other EWIS components.
• Hydraulic fluid
• Battery electrolytes
• Fuel
• Corrosion inhibiting compounds
• Waste system chemicals 18
• 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.