(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.
(2) Clean only contaminated areas and items. Before cleaning, make sure that the cleaning materials and methods will not cause more contamination. Make sure cloths used are clean, dry, and lint-free. Connectors should be completely dry before mating. Fluids left on connectors can have a deteriorating effect on the connector or the system or both.
h. Servicing or Repairing Waste/Water Systems. EWIS in areas adjacent to waste/water systems are prone to contamination from those systems. Use care to prevent fluids from reaching EWIS components while servicing or repairing waste/water systems, and cover exposed EWIS components while working. Operator practice may call for a weak acid solution to be periodically flushed through lavatory systems to improve reliability and efficiency of operation.
Because of the effect of acid contamination on systems and structure, confirm that the system is free of leaks before using such solutions.
i. Servicing or Repairing Oil Systems. EWIS in areas adjacent to oil systems are prone to contamination from those systems. Oil and debris in combination with damaged wiring can present a fire hazard. To minimize the attraction and adhesion of foreign material, use care to prevent fluids from reaching EWIS components while servicing or repairing oil systems.
j. Servicing or Repairing Hydraulic Systems. EWIS in areas adjacent to hydraulic systems are prone to contamination from those systems. To minimize the attraction and adhesion of foreign material, use care to prevent fluids from reaching EWIS components while servicing or repairing hydraulic systems.
k. Gaining Access (Entering Zones). When entering the airplane or working on it, use care to prevent damage to adjacent EWIS components, including wiring or other EWIS components that may be hidden from view (for example, covered by insulation blankets). Use protective boards or platforms for adequate support and protection. Avoid using wire bundles as handholds, steps, and supports. Do not use wiring to hang or support work lights. If wiring must be displaced or removed for work area access, it should be adequately released from its clamping or other restraining provisions to allow movement without damage, and it should be returned to position after work is completed.
l. Applying Corrosion Prevention Compounds (CPC). When applying CPC in airplane zones containing EWIS, use care to prevent CPC from contacting it. Dust and lint are more likely to collect on wire that has CPC on it. Apply CPCs according to the airplane manufacturer’s maintenance instructions.
/s/ Ali Bahrami Manager, Transport Airplane Directorate Aircraft Certification Service 31
Appendices Appendices Appendix A. The Enhanced Zonal Analysis Procedure (EZAP)
Appendix B. Evaluating Whether a Design Change Impacts Previously Approved EWIS ICA and Developing any Necessary New or Revised EWIS ICA as Required by § 26.11(c) or § 25.1729 Appendix C. Definitions Appendix D. FAA Oversight Offices for the Purposes of Part 26 Appendix E. Applicable Regulations and Relevant Preamble Discussion Appendix F. Background Appendix G. Related Regulations and Documents Appendix H. EZAP Worksheets for Use by Applicants
Appendix A Appendix A
1. The Enhanced Zonal Analysis Procedure (EZAP). The figures and explanations on the following pages describe the EZAP process. Before you begin using this logic, you should be thoroughly familiar with the contents and philosophy of this AC and the results the AC and the EZAP seek to achieve.
A-1
Appendix A Identify aircraft zones, including boundaries Figure 1 Enhanced Zonal Analysis List details of zone, for example:
Procedure Access Installed equipment Lightning/HIRF protection features EWIS installation Possible combustible materials YES Does the zone contain EWIS?
NO likely to be, combustible Are there, or are there Is wiring or other EWIS materials in the zone? NO close (2 in/50 mm) components -NO→ to both primary and backup hydraulic, mechanical, or electrical flight controls?
No further analysis is required for the zone.
An inspection or restoration task applicable to EWIS is not necessary for the zone.
Is there an effective task to significantly reduce the likelihood of -NO- accumulation of combustible Select EWIS inspection materials? level and interval See figure 2 YES
CONTINUE THE Define the task and ANALYSIS assign an interval for INSPECTION TASK(S) performing it.
• STAND-ALONE GVI GVI CONSOLIDATED
• DET Consider consolidation with existing IN ZONAL
• Cleaning (Restoration) inspection tasks in systems and INSPECTION
• Any other tasks powerplant and/or zonal programs * identified as applicable and effective to maintain EWIS safety * Section 26.11(b) requires Assign task to EWIS ICA EWIS ICA and fuel tank Assign task to EWIS ICA maintenance program systems and system ICA developed to Maintenance program zonal section powerplant section comply with SFAR 88 be Recommend inclusion in ATA 20 compatible and any Airplanes with ZIPs redundancies between them minimized.
A-2
From figure 1, step 8 Figure 2 05/04/10 Using rating tables, assess zone attributes to determine appropriate level of inspection Step 8 - (examples provided in appendix B of this AC) EWIS Inspection Level and Interval Selection
PROGRAMS WITH ZONAL PROGRAMS WITHOUT ZONAL
INSPECTION PROGRAM INSPECTION PROGRAM Is zonal GVI alone effective YES • List zone description and zone at same interval effective Is GVI of all EWIS in the YES • boundaries for GVI of all EWIS List zone description and for all EWIS in the zone? boundaries for zonal GVI for all EWIS in the zone? in the zone NO NO Define specific EWIS in the Define specific EWIS in the zone for which stand-alone zone for which GVI at more GVI is justified frequent interval is justified Zonal GVI must be augmented Some EWIS requires GVI at with stand-alone GVI and/or more frequent interval and/or DET inspection DET inspection Define specific EWIS in the Define specific EWIS in the zone for which DET is justified zone for which DET is justified Using rating tables, assess likelihood of damage to EWIS in the Appendix A AC 25-27A zone to determine an appropriate interval for each inspection task identified (example provided in appendix B of this AC)
Appendix A
2. Explanation for Steps in EZAP Logic Diagrams. The following paragraphs provide further explanation of each step in the enhanced zonal analysis procedure (EZAP) logic (figures 1 and 2 of this appendix). If you are developing EWIS ICA because you are required to do so by § 26.11(b), then you must use the “representative airplane” as required by that section.
(See paragraph 2c of this AC.) All applicants should, whenever possible, verify the results of the analysis using an actual aircraft (typical airplane that has not been cleaned) to ensure that they fully understand the zones being analyzed. Using an actual airplane will help in determining density, size, types and levels of contaminants or combustible materials, and environmental and accidental damage issues for each zone.
STEP 1: Identify aircraft zones, including boundaries.
According to Air Transport Association (ATA) iSpec 2200, Information Standards for Aviation Maintenance, zones are identified by the airplane manufacturer “to facilitate maintenance, planning, preparation of job instructions, location of work areas and components, and a common basis for various maintenance tasks.” ATA iSpec 2200 contains guidelines for determining airplane zones and their numbering. The EZAP process uses these manufacturer-identified zones. The zones are not created uniquely for EZAP.
However, if the design approval holder or operator has not already established aircraft zones, we recommend that this be done. Wherever possible, the definition of zones should follow a consistent method such as ATA iSpec 2200 (formerly ATA Spec 100), varied only to accommodate particular design constructional differences.
Define the zones, wherever possible, by actual physical boundaries such as wing spars, major bulkheads, cabin floor, control surface boundaries, skin, and so forth, and include access provisions for each zone.
STEP 2: List details of zone.
Within the zone, identify system installations, significant components, lightning and high intensity radiated field (L/HIRF) protection features, typical power levels in any installed wiring bundles, combustible materials (present or with the potential for accumulation) and any other features that may affect EWIS integrity or accumulation of combustibles.
With respect to power levels, the person performing the EZAP analysis should know whether the wire bundle consists primarily of main generator feeder cables, low voltage instrumentation wiring, or standard bus wiring. This information will be used in determining potential effects of deterioration.
Identify any locations where both primary and back-up flight controls are routed within 2 inches/50 mm of a wiring harness or other EWIS components. This information is required to answer the question in step 7.
STEP 3: Does zone contain EWIS? This question eliminates from the EZAP those zones that do not contain EWIS.
A-4