Appendix C inspections, processes, procedures, and airworthiness limitations required to keep the airplane airworthy throughout its operational life.
22. Lightning/High Intensity Radiated Field (L/HIRF) Protection—The protection of airplane electrical systems and structure from induced voltages or currents by means of shielded wires, raceways, bonding jumpers, connectors, composite fairings with conductive mesh, static dischargers, and the inherent conductivity of the structure; may include airplane specific devices, for example, radio frequency (RF) gaskets.
23. Maintenance—As defined in 14 CFR 1.1, “maintenance means inspection, overhaul, repair, preservation, and the replacement of parts, but excludes preventive maintenance.” For the purposes of this advisory circular, maintenance also includes preventive maintenance, as described in both § 1.1 and paragraph (c) of appendix C to 14 CFR part 43. Section 1.1 of 14 CFR provides the following definition: “Preventive maintenance means simple or minor preservation operations and the replacement of small standard parts not involving complex assembly operations.” Paragraph (c) of appendix A to 14 CFR part 43 lists the tasks that are considered preventive maintenance.
24. Maintenance Instructions—Information that provides recommended periods for cleaning, inspection, adjustment, testing, lubrication, degree of inspection, applicable wear tolerances, and recommended work necessary for each part of the airplane and its engine auxiliary power units, propellers, accessories, instruments, and equipment to provide for continued airworthiness of the airplane. Recommended overhaul periods and necessary cross-references to the Airworthiness Limitations section of the maintenance manual are also included.
25. Maintenance Significant Item (MSI)—Items (system or component) identified by the manufacturer whose failure could have one or more of the following results or characteristics:
• Could affect safety (on ground or in flight).
• Is undetectable during operations (on ground or in flight).
• Could have significant operational impact.
• Could have significant economic impact.
26. Maintenance Review Board Report (MRBR)—A report intended for use by air carriers that contains the initial minimum scheduled maintenance and inspection requirements for a particular transport category airplane maintenance program. Air carriers use the MRBR and its associated requirements to develop maintenance programs. See AC 121-22A, Maintenance Review Board Procedures, for more information.
27. Maintenance Steering Group 3 (MSG-3)—MSG-3 is a document issued by the ATA that addresses the development of scheduled maintenance using an analytical procedure contained within the document. As stated in the document, its objective is “. . . to present a means for developing the scheduled maintenance tasks and intervals which will be acceptable to the regulatory authorities, the operators, and the manufacturers. The scheduled maintenance task and interval details will be developed by coordination with specialists from the operators, C-4
Appendix C manufacturers, and the regulatory authority of the country of manufacture. Specifically, this document outlines the general organization and decision processes for determining scheduled maintenance requirements initially projected for the life of the aircraft and/or powerplant.”
28. Needling—The puncturing of a wire’s insulation to make contact with the core to test the continuity and presence of voltage in the wire segment.
29. Special Federal Aviation Regulation No. 88 (SFAR 88)—SFAR 88 was issued in 2001 as part of FAA final rule “Transport Airplane Fuel Tank System Design Review, Flammability Reduction, and Maintenance and Inspection Requirements,” Docket No. FAA-1999-6411.
SFAR 88 requires the design approval holder to perform a safety review of the fuel tank system to show that fuel tank fires or explosions will not occur on airplanes of the approved design. In conducting the review, the design approval holder must demonstrate compliance with the new standards adopted for § 25.981(a) and (b) and the existing standards of § 25.901.
30. Source Document (SD)—A single document required by paragraph H25.5(b) to appendix H of 14 CFR part 25, which identifies all of the components comprising the EWIS ICA. The SD must either contain all of the required EWIS ICA, or reference other documents that contain that information.
31. Stand-Alone GVI—A general visual inspection that is not performed as part of a zonal inspection. Even in cases where the interval coincides with the zonal inspection, the stand-alone GVI remains an independent step on the work card.
32. Structural Significant Item (SSI)—Any detail, element, or assembly that contributes significantly to carrying flight, ground, pressure, or control loads and whose failure could affect the structural integrity necessary for the safety of the airplane.
33. Swarf—British term used to describe the metal particles generated from drilling and machining operations. Such particles may accumulate on and between wires within a wire bundle.
34. Standard Wiring Practices Manual (SWPM) (may also be known as the Electrical Standards Practice Manual (ESPM))—A manual (either in book or electronic form) produced by an airplane manufacturer containing information detailing procedures and practices for the universal repair and maintenance of electrical wire, cable bundles, and coaxial cables. Standard practices include procedures and practices for the inspection, installation, and removal of electrical systems components or other EWIS components, including methods of bundle attachment, wire splices, connectors and electrical terminal connections, and bonding/grounding.
35. Transport Airplane Directorate (TAD)—The FAA’s directorates (Engines and Propellers, Rotorcraft, Small Airplanes, and Transport Airplane) develop and implement national regulatory requirements, policy and procedures for continued operational safety, and type, production, and airworthiness certifications for their designated products. Each directorate also has responsibility for overseeing certification activities (field office operations, certification programs, and projects) within its geographic area. TAD has oversight responsibility for transport category airplane design approvals and modifications worldwide, as well as oversight responsibility for C-5
Appendix C over 900 production approval holders. TAD works closely with other FAA offices throughout the country and with foreign regulatory authorities to accomplish this mission.
36. Zonal Inspection—A collective term comprising selected general visual inspections and visual checks that are applied to each airplane zone, defined by access and area, to check system and power plant installations and structure for security and general condition. Zonal inspections are discussed in greater detail in section 10 of this AC.
37. Zonal Inspection Program (ZIP)—A part of an airplane model’s overall maintenance program where the whole of the airplane is divided into zones. For each zone of the airplane, applicable maintenance instructions are identified.
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Appendix D Appendix D
1. FAA Oversight Offices for the Purposes of Part 26. Table 1 lists the FAA oversight offices, as currently determined by the Administrator, that oversee issuance of type certificates and amended type certificates for manufacturers of transport category airplanes with a passenger capacity of 30 passengers or a payload capacity of 7,500 pounds or greater.
Table 1. FAA Oversight Offices for Issuance of TCs and Amended TCs Airplane Manufacturer FAA Oversight Office Aerospatiale Transport Airplane Directorate, International Branch, ANM-116 Airbus Transport Airplane Directorate, International Branch, ANM-116 BAE Transport Airplane Directorate, International Branch, ANM-116 Boeing Puget Sound Seattle Aircraft Certification Office Boeing Long Beach Los Angeles Aircraft Certification Office Bombardier New York Aircraft Certification Office CASA Transport Airplane Directorate, International Branch, ANM-116 deHavilland New York Aircraft Certification Office Dornier Transport Airplane Directorate, International Branch, ANM-116 Embraer Transport Airplane Directorate, International Branch, ANM-116 Fokker Transport Airplane Directorate, International Branch, ANM-116 Lockheed Atlanta Aircraft Certification Office McDonnell-Douglas Los Angeles Aircraft Certification Office SAAB Transport Airplane Directorate, International Branch, ANM-116 D-1
Appendix E Appendix E
1. Applicable Regulations and Relevant Preamble Discussion.
a. The text of the regulations referred to in this AC is reproduced here for easy reference.
This information is provided as reference only. If any deviation exists between the reference material provided here and the regulations contained in the Code of Federal Regulations (CFR), it is the regulations in the CFR that must be complied with. We have also included here the applicable preamble discussions from the EAPAS/FTS Notice of Proposed Rulemaking (NPRM) issued on October 5, 2005 (70 FR 58508). The preamble discussion for a particular regulation follows the text of that regulation. You should refer to the NPRM and the final rule for a complete discussion of the requirements. Only the most relevant text from those discussions has been reproduced here.
b. Comments received about the NPRM are summarized and discussed in the final rule.
You can download a copy of the Final Rule from the Internet at http://www.gpoaccess.gov/cfr/.
Mail, telephone, and fax request information is given in appendix G.
2. Part 25
a. Section 25.1701.
Ҥ 25.1701 Definition.
(a) As used in this chapter, electrical wiring interconnection system (EWIS) means any wire, wiring device, or combination of these, including termination devices, installed in any area of the airplane for the purpose of transmitting electrical energy, including data and signals, between two or more intended termination points. This includes:
(1) Wires and cables.
(2) Bus bars.
(3) The termination point on electrical devices, including those on relays, interrupters, switches, contactors, terminal blocks and circuit breakers, and other circuit protection devices.
(4) Connectors, including feed-through connectors.
(5) Connector accessories.
(6) Electrical grounding and bonding devices and their associated connections.
(7) Electrical splices.
(8) Materials used to provide additional protection for wires, including wire insulation, wire sleeving, and conduits that have electrical termination for the purpose of bonding.
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Appendix E
(9) Shields or braids.
(10) Clamps and other devices used to route and support the wire bundle.
(11) Cable tie devices.
(12) Labels or other means of identification.
(13) Pressure seals.
(14) EWIS components inside shelves, panels, racks, junction boxes, distribution panels, and back-planes of equipment racks, including, but not limited to, circuit board back-planes, wire integration units, and external wiring of equipment.
(b) Except for the equipment indicated in paragraph (a)(14) of this section, EWIS components inside the following equipment, and the external connectors that are part of that equipment, are excluded from the definition in paragraph (a) of this section:
(1) Electrical equipment or avionics that are qualified to environmental conditions and testing procedures when those conditions and procedures are—
(i) Appropriate for the intended function and operating environment, and
(ii) Acceptable to the FAA.
(2) Portable electrical devices that are not part of the type design of the airplane. This includes personal entertainment devices and laptop computers.
(3) Fiber optics.”
b. Section 25.1729.
(1) Regulation.
Ҥ 25.1729 Instructions for Continued Airworthiness: EWIS.
The applicant must prepare Instructions for Continued Airworthiness applicable to EWIS in accordance with Appendix H sections H25.4 and H25.5 to this part that are approved by the FAA.”
(2) NPRM Preamble Discussion (70 FR 58526, October 6, 2005). (§ 25.1729 was proposed as § 25.1739).
“Section 25.1739 Instructions for Continued Airworthiness: EWIS.
Proposed § 25.1739 would require that applicants prepare EWIS ICA in accordance with the requirements of Appendix H to part 25. The proposed EWIS ICA requirements are discussed in the next section of this document.”
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Appendix E
c. Part 25, Appendix H, Section H25.5.
(1) Regulation.
“H25.5 Electrical Wiring Interconnection System (EWIS) Instructions for Continued Airworthiness.
(a) The applicant must prepare Instructions for Continued Airworthiness (ICA) applicable to EWIS as defined by § 25.1701 that are approved by the FAA and include the following:
(1) Maintenance and inspection requirements for the EWIS developed with the use of an enhanced zonal analysis procedure that includes:
(i) Identification of each zone of the airplane.
(ii) Identification of each zone that contains EWIS.
(iii) Identification of each zone containing EWIS that also contains combustible materials.
(iv) Identification of each zone in which EWIS is in close proximity to both primary and back-up hydraulic, mechanical, or electrical flight controls and lines.
(v) Identification of— (A) tasks, and the intervals for performing those tasks, that will reduce the likelihood of ignition sources and accumulation of combustible material, and (B) procedures, and the intervals for performing those procedures, that will effectively clean the EWIS components of combustible material if there is not an effective task to reduce the likelihood of combustible material accumulation.
(vi) Instructions for protections and caution information that will minimize contamination and accidental damage to EWIS, as applicable, during performance of maintenance, alteration, or repairs.
(2) Acceptable EWIS maintenance practices in a standard format.
(3) Wire separation requirements as determined under § 25.1707.
(4) Information explaining the EWIS identification method and requirements for identifying any changes to EWIS under § 25.1711.
(5) Electrical load data and instructions for updating that data.
(b) The EWIS ICA developed in accordance with the requirements of H25.5(a)(1) must be in the form of a document appropriate for the information to be provided, and they must E-3
Appendix E be easily recognizable as EWIS ICA. This document must either contain the required EWIS ICA or specifically reference other portions of the ICA that contain this information.”
(2) NPRM Preamble Discussion for Section H25.5 (70 FR 58532, October 6, 2005).
“Appendix H to Part 25—Instructions for Continued Airworthiness As previously noted, improper maintenance, repair, and modifications often hasten the “aging” of EWIS. To properly maintain, repair, and modify airplane EWIS, certain information must be available to the designer, modifier, and installer. This information should be part of the ICA as required by current § 25.1529 and the proposed § 25.1739.
This proposal would amend Appendix H by adding a new section, H25.5, to require TC applicants to develop maintenance information for EWIS as part of the ICA as a requirement for getting a design approval. The proposed rule would also apply to applicants for design change approvals (supplemental TCs and amended TCs).
The proposal would require applicants for TCs to prepare ICA for EWIS that are approved by the FAA Oversight Office, in the form of a document that is easily recognizable as an EWIS ICA. To prepare these instructions, they must use an EZAP such as the one described in AC120-XX, “Program to Enhance Aircraft Electrical Wiring Interconnection System Maintenance” to perform a review of their representative airplane covering all areas, including the flightdeck (also known as the cockpit), electrical power center, fuel tank wiring and powerfeeder cables, as well as the engine. Applicants for design change approvals would have to perform a similar review for their proposed design changes.
A zonal analysis procedure is an assessment of the structures and systems within each physical zone of the airplane. It is used to develop an inspection program to assess the general condition and security of attachment of all system components and structures items contained in the zone, using general visual inspections (GVI). An enhanced zonal analysis procedure (EZAP) is an enhanced version of the zonal analysis procedure. It focuses on EWIS components. An EZAP-generated inspection program might call for the use of stand-alone GVI and detailed inspections (DET). A stand-alone GVI is one that is performed separately from the regularly scheduled GVI (typically more frequently) and is focused on a particular area or component. In this case, the focus would be wiring. So while the zonal analysis procedure would result in a regularly scheduled GVI for the entire zone, in which each of its systems and structures are inspected at the same time, the EZAP could result in additional GVIs or DETs for the EWIS in that zone, which occur more frequently. These inspection techniques are discussed later in this section.
An EZAP identifies the physical and environmental conditions contained in each zone of an airplane, analyzes their effects on electrical wiring, and assesses the possibilities for smoke and fire. From such an analysis, maintenance tasks can be developed to prevent ignition sources and to minimize the possibilities for combustion by minimizing the accumulation of combustible materials. Such a procedure would involve dividing the airplane into physical areas, or zones, including actual physical boundaries such as wing spars, bulkheads, and cabin floor, and access provisions for the zone, and identifying which of those zones contain EWIS components. For E-4
Appendix E those zones with EWIS components, characteristics and components of all systems installed in the zone would be listed. The EWIS in the zone would be described, including information on the full range of power levels carried in the zone. And the presence or possibilities for ignition sources or accumulation of combustibles would be noted.
Combustibles are any materials that could cause a fire to be sustained in the event of an ignition source. Examples of combustible materials would be dust or lint accumulation, contaminated insulation blankets, and fuel or other combustible liquids or vapors. Wire contaminants are foreign materials that are likely to cause degradation of wiring. Wire contaminants can also be combustibles. Some commonly used airplane liquids, like engine oils, hydraulic fluids, and corrosion prevention compounds, might be readily combustible, but only in vapor or mist form. In that case, an assessment must be made of conditions that could exist within the zone that would convert the liquid to that form. Combustibles appearing as a result of any single failure must be considered. An example would be leaks from connection sites of unshrouded pipes. For the purposes of this new requirement, the term combustible does not refer to material that will burn when subjected to a continuous source of heat as occurs when a fire develops. Combustibles, as used here, will sustain a fire without a continuous ignition source.
An EZAP must address:
• Ventilation conditions in the zone and the density of the installations that would affect the presence and build-up of combustibles and the possibilities for combustion. Avionics and instruments located in the flightdeck and equipment bays, which generate heat and have relatively tightly packed installations, require cooling air flow. The air blown into the area for that cooling tends to deposit dust and lint on the equipment and EWIS components.
• Liquid contamination on wiring. Most synthetic oils and hydraulic fluids, while they might not be combustibles by themselves, could be an aggravating factor for accumulation of dust or lint. This accumulation could then present fuel for fire. Moisture on wiring may increase the probability of arcing from small breaches in the insulation, which could cause a fire.
Moisture on wires that contain insulation breaches can also lead to “arc tracking.” As discussed previously, arc tracking is a phenomenon in which an electrical arc forms a conductive carbon path across an insulating surface. The carbon path then provides a short circuit path through which current can flow. Short circuit current flow from arc tracking can lead to loss of multiple airplane systems, structural damage, and fire.
• EWIS in close proximity to both primary and back-up hydraulic, mechanical, or electrical flight controls.
• The type of wiring discrepancies that must be addressed if they are identified by general visual or detailed inspections. A listing of typical wiring discrepancies that should be detectable during EZAP-derived EWIS inspections is given in AC120-XXX, Section B “Guidance for Zonal Inspections.”
• Proper cleaning methods for EWIS components.
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Appendix E Once information about such contaminants and combustibles within an airplane zone is collected, each identified possibility for combustion would then be addressed to determine whether a specific task could be performed to reduce that possibility. An example of a specific task to reduce build-up of combustibles on EWIS components is the use of temporary protective covers (such as plastic sheeting) over EWIS components in a zone where corrosion prevention fluids are being used. This would minimize the amount of fluid contamination of the EWIS components. Preventing fluid contamination reduces the probability of other contaminants, like dust and dirt, accumulating on the EWIS components. If no task can be developed to prevent accumulation of combustibles in a zone, such as the dust blown through the air by cooler fans, then tasks must be developed to minimize their buildup, such as scheduled cleaning.
Developing an ICA to define such tasks would include assessing whether particular methods of cleaning would actually damage the EWIS components. Although regular cleaning to prevent potential combustible build-up would be the most obvious task for an EWIS ICA, other procedures might also be called for. A detailed inspection of a hydraulic pipe might be appropriate, for instance, if high-pressure mist from a pinhole caused by corrosion could accumulate on a wire bundle in a low ventilation area, creating a possibility for electrical arcing.
Proximity of EWIS to both primary and back-up hydraulic, mechanical, or electrical flight controls within a zone would affect the criticality of inspections needed, their level of detail, and their frequency. Even in the absence of combustible material, wire arcing could adversely affect continued safe flight and landing if hydraulic pipes, mechanical cables, or wiring for fly-by-wire controls are routed close to other wiring.
The EZAP-generated ICA must be produced in the form of a single document, easily recognizable as EWIS ICA for that specific airplane model. The single document is relevant to the maintenance and inspection aspects of the ICA, and not the standard wiring practices manual or electrical load analysis, etc.
The ICA must define applicable and effective tasks, and the intervals for performing them, to:
• Minimize accumulation of combustible materials.
• Detect wire contaminants
• Detect wiring discrepancies that may not otherwise be reliably detected by inspections contained in existing maintenance programs.
As noted earlier, among the types of tasks to be developed from an EZAP are general visual inspections (GVI) and detailed inspections (DET). A GVI is defined as 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 of the inspected object unless otherwise specified. It 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. It may be necessary to use a mirror to improve visual access to all exposed surfaces in the inspection area. Stands, ladders, or platforms may be required to E-6
Appendix E gain proximity to the area being checked. It is expected that the area to be inspected is clean enough to minimize the possibility that accumulated dirt, grease, or other contaminants might hide unsatisfactory conditions that would otherwise be obvious. It is also expected, as an outcome of the EZAP applied to EWIS, that any cleaning considered necessary would be performed in accordance with procedures that minimize the possibility of the cleaning process itself introducing anomalies. The EZAP must identify guidelines to assist personnel performing a GVI in identifying wiring discrepancies and in assessing what effect such discrepancies, if found, could have on adjacent systems, particularly if these include wiring. As discussed previously, a list of typical wiring discrepancies that should be addressed is contained in proposed AC120-XX, Section B, “Guidance for Zonal Inspections.”
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 considered 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. It may include tactile assessment to check a component or assembly for tightness and security. Such an inspection may be needed to ensure the continued integrity of installations such as bonding jumpers, terminal connectors, etc.
A DET would be required when the developer of the EZAP determines that a GVI is inadequate to reliably detect anomalies or degradation of EWIS components. Any detected discrepancies must be corrected according to the operator’s approved maintenance procedures.
It is not intended that the EZAP ICA identify how to correct detected discrepancies.
To prevent improper modification and repair of existing EWIS or the improper installation of a new EWIS, modification designers and modification personnel must know the applicable standard wiring practices, EWIS identification requirements, and electrical load data for the airplane undergoing modification. The proposed Appendix H25.5 would also require that the following information be included in ICA applicable to EWIS:
• Standard wiring practices data.
• Wire separation design guidelines.
• Information to explain the airplane’s EWIS identification method required by the proposed § 25.1711.
• Electrical load data and instructions for updating that data. Such information will help ensure that those modifying, repairing, or installing new EWIS will not perform any action that will adversely affect previously certified systems and unintentionally introduce potential hazards.
Standard wiring practices are defined as standards developed by the specific airplane manufacturer or industry-wide standards for the repair and maintenance of EWIS. They include procedures and practices for the installation, repair, and removal of EWIS components, including information about wire splices, methods of bundle attachment, connectors and electrical terminal E-7
Appendix E connections, bonding, and grounding. Although a standard wiring practices manual is not a design manual, and those designing a new EWIS modification for a specific model airplane should not use it as such, it does provide the designer with insight into the types of EWIS components used by the TC holder and the procedures recommended by the manufacturer for maintenance or repair that supports continued airworthiness of the components.
EWIS separation guidelines are important for maintaining the safe operation of the airplane. Maintenance and repair personnel need to be aware of the type certificate holders’ separation requirements so they do not compromise separation in previously certified systems.
In fuel tank systems, the separation of certain wires may be critical design configuration control items and therefore qualify as an airworthiness limitation. Maintenance personnel need to be aware of these guidelines and limitations because many times wire bundles must be moved or removed to perform necessary maintenance. They must be able to readily identify EWIS associated with systems essential to the safe operation of the airplane.
Similarly, those who design and install new EWIS need to be aware of separation requirements so they can use the same methods to develop the required separation for the EWIS they are adding to the airplane. This would help to ensure both that newly added EWIS is adequately separated from other EWIS, airplane system components, and structure so they do not damage the added EWIS, and that the addition of the new EWIS does not invalidate separation for previously certified EWIS.
Electrical load data and the instructions for updating that data are necessary to help ensure that future modifications or additions of equipment that consume electrical power do not exceed the generating capacity of the onboard electrical generation and distribution system. The existing § 25.1351(a)(1) mandates that the required generating capacity, and the number and kinds of power sources, must be determined by an electrical load analysis. Typically, after an airplane is delivered and enters service, it is modified numerous times throughout its service life.
Each addition or deletion of an electrical-power-consuming system changes the electrical load requirements. The only way to ensure that the capacity of the overall generating and distribution system, as well as individual electrical buses, is not exceeded is to have an up-to-date electrical load analysis. The best way to ensure that an up-to-date electrical load analysis is maintained is for the type certificate holder to include such data in the ICA provided with the airplane when it is first delivered to a customer, along with recommended practices for keeping it updated as electrical loads are deleted and added.”
3. Part 26
a. Section 26.3.
Ҥ 26.3 Definitions For the purposes of this part:
FAA Oversight Office is the aircraft certification office or office of the Transport Airplane Directorate with oversight responsibility for the relevant type certificate, supplemental type certificate, or manufacturer, as determined by the Administrator.”
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