attachment, connectors and electrical terminal connections, bonding, and grounding. A SWPM is not a design manual, and designers of EWIS modifications for specific airplane models should not use it as such. But 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.
Advisory Circular 25-26, Development of Standard Wiring Practices Documentation, provides guidance on how to comply with the requirements of paragraph H25.5(a)(2) of Appendix H to part 25.
(5) H25.5(a)(3). This section requires applicants to include EWIS separation requirements in the ICA. EWIS separation requirements are important for maintaining the safe operation of the airplane. Maintenance and repair personnel need to be aware of the type certificate holder’s separation requirements so they do not compromise separation in previously certified systems. This requirement will help maintenance, repair, and modification personnel easily determine EWIS separation requirements.
(a) Determination of EWIS separation requirements is required by § 25.1707. To comply with H25.5(a)(3), the applicant needs to develop a way to convey these separation requirements and place them in the ICA.
For example, if an airplane has a fly-by-wire flight control system and a minimum of 2 inches of physical separation is needed between the EWIS associated with the flight control system and other EWIS, this information must to be available in the ICA. Similarly, the separation of certain wires in fuel tank systems may be critical design configuration control items and therefore qualify as an airworthiness limitation. Maintenance personnel need these separation requirements and limitations because many times wire bundles must be moved or removed to perform maintenance.
(b) The separation data included in the ICA can take many forms. If a particular airplane model has fly-by-wire flight controls, the manufacturer may designate the EWIS associated with the flight control systems by a certain identification scheme (as required by § 25.1711), and in the ICA state that EWIS so designated must be maintained with XX amount of separation from all other EWIS and YY amount of separation from other airplane systems and structure. The manufacturer can then repeat this information for other EWIS associated with other airplane systems. The ICA could indicate how EWIS associated with IFE and other passenger convenience systems is identified, and that this EWIS must be maintained XX inches from other categories of EWIS or structure.
(c) It is not the intent of the regulation to require a design approval holder or an applicant to divulge proprietary information in order to comply.
Certain information, however, needs to be made available to modifiers and 45
maintainers to ensure that future modifications and repairs do not invalidate previously certified designs.
(6) H25.5(a)(4). This paragraph requires that the ICA contain information explaining the EWIS identification method and requirements for identifying any changes to EWIS. This requirement is intended to ensure that future modifications adding EWIS identify those added EWIS with the same type of identification scheme used by the original airplane manufacturer. This information will help modification designers and modification personnel avoid improper modification and repair of existing EWIS or improper installation of new EWIS. These personnel need to review the applicable standard wiring practices, EWIS identification requirements, and electrical load data for the airplane they are modifying.
(7) H25.5(a)(5).
(a) This paragraph requires that the ICA contain electrical load data and instructions for updating that data. Electrical load data and the instructions for updating it 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. Maintaining a record of actual airplane electrical loads is important to ensure that modifications to the original design do not impose electrical loads on the electrical generating system in excess of the system’s capability to provide the necessary power and maintain necessary margins.
To comply with the requirements of this paragraph applicants need to provide:
1 Electrical generating capacity of each source of normal electrical power generation.
2 Electrical generating capacity of each source of emergency power generation.
3 Electrical load capacity of each electrical bus.
4 Actual electrical loading of each electrical bus.
(b) The airplane manufacturer is responsible for preparing, and including in the ICA, the electrical load data as required by this section for the “asdelivered” airplane. It is then the responsibility of subsequent modifiers to update the electrical load data when the proposed modification requires the data to be revised (i.e., when required by § 25.1351(a)).
The airplane manufacturer is responsible for preparing, and including in the ICA, the electrical load data as required by this section for the “as-delivered” airplane. It is then the responsibility of subsequent modifiers to update the electrical load data when the proposed modification requires the data to be revised (i.e., when required by § 25.1351(a)).
Appendix A
APPENDIX A
RELATED REGULATIONS AND DOCUMENTS
REGULATIONS. You can download an electronic copy of 14 CFR from the Internet at http://www.gpoaccess.gov/cfr/. A paper copy can be ordered by sending a request to the U.S. Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402-0001, or by calling telephone number (202) 512-1800; or by sending a request by facsimile to (202) 512-2250.
• § 25.773 Pilot compartment view.
• § 25.831 Ventilation.
• § 25.863 Flammable fluid fire protection.
• § 25.869 Fire protection: systems.
• § 25.899 Electrical bonding and protection against static electricity.
• § 25.903 Engines.
• § 25.981 Fuel tank ignition prevention.
• § 25.1165 Engine ignition systems.
• § 25.1189 Shutoff means.
• § 25.1203 Fire detector system.
• § 25.1301 Function and installation.
• § 25.1303 Flight and navigation instruments.
• § 25.1309 Equipment, systems, and installations.
• § 25.1310 Power source capacity and distribution.
• § 25.1316 System lightning protection.
• § 25.1331 Instruments using a power supply.
• § 25.1351 General.
• § 25.1353 Electrical equipment and installations.
• § 25.1355 Distribution system.
• § 25.1357 Circuit protective devices.
• § 25.1360 Precautions against injury.
• § 25.1362 Electrical supplies for emergency conditions.
• § 25.1365 Electrical appliances, motors, and transformers.
• § 25.1431 Electronic equipment.
• § 25.1529 Instructions for Continued Airworthiness.
A-1
Appendix A OTHER RELATED CFR PARTS.
Part 21 Certification Procedures for Products and Parts
Part 43 Maintenance, Preventive Maintenance, Rebuilding, and Alteration
Part 91 General Operating and Flight Rules
Part 121 Operating Requirements: Domestic, Flag, and Supplemental Operations
Part 125 Certification and Operations: Airplanes having a Seating Capacity of 20 or More Passengers or a Maximum Payload Capacity of 6,000 Pounds or More: and Rules Governing Persons on Board Such Aircraft
Part 129 Operations: Foreign Air Carriers and Foreign Operators of U.S.- Registered Aircraft Engaged in Common Carriage
Part 145 Repair Stations
ADVISORY CIRCULARS. You can download an electronic copy of the latest version of the following ACs from the FAA Internet at http://rgl.faa.gov.
• 25-10 Guidance for Installation of Miscellaneous, Nonrequired Electrical Equipment
• 25-16 Electrical Fault and Fire Protection and Prevention
• 43-13.1B Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair
• 25.773-1 Pilot Compartment View Design Considerations
• 25-869-1 Electrical Smoke and Fire Protection
• 25.981-1B Fuel Tank Ignition Source Prevention Guidelines
• 25.1309-1A System Design and Analysis
• 25.1310-1 Power Source Capacity and Distribution
• 25.1353-1 Electrical Requirements and Installations
• 25-1357-1 Circuit Protective Device Accessibility
• 25-1360-1 Electric Shock and Burns
• 25-1362 Electrical Supply for Emergency Service
• 25.1363-1 Electrical System Tests
• 25-26 Development of Standard Wiring Practices Documentation
• 25-27 Development of Transport Category Airplane Electrical Wiring Interconnection Systems Instructions for Continued Airworthiness Using an Enhanced Zonal Analysis Procedure
A-2
Appendix A POLICY MEMORANDA. You can download an electronic copy of the latest version of the following policy memoranda from the FAA Internet at http://rgl.faa.gov.
PS-ANM100-1999-0021 Requir ements of FAR 25.1357(e)
PS-ANM100-2000-00105 Interim Policy Guidance for Certification of In-Flight Entertainment Systems on Title 14 CFR Part 25 Aircraft
PS-ANM100-2001-00113 Interim Summary of Policy and Advisory Material Available for Use in the Certification of Cabin Mounted Video Camera Systems with Flight Deck Displays on Title 14 CFR Part 25 Aircraft
PS-ANM111-2002-01-04 System Wiring Policy for Certification of Part 25 Airplanes
REPORTS.
“Task 6 Final Report” Aging Transport Systems Rulemaking Advisory Committee, dated October 29, 2002.
(http://www.mitrecaasd.org/atsrac/final_reports/Task_6_Final_Report-10-29- 2002.pdf)
SOCIETY OF AUTOMOTIVE ENGINEERS (SAE) DOCUMENTS.
(http://www.sae.org/servlets/index)
NOTE: AS = Aerospace Standard AIR = Aerospace Information Report ARP = Aerospace Recommended Practice
AS4373 Test Methods for Insulated Electric Wire
AS50881 Wiring Aerospace Vehicle
AS70991 Terminals: Lug and Splice, Crimp Style, Aluminum, For Aluminum Aircraft Wire
AS7928 Terminals, Lug: Splices, Conductor: Crimp Style, Copper, General Specification For
AS81824 Splices, Electric, Permanent, Crimp Style Copper, Insulated, Environment Resistant
A-3
Appendix A AIR5575 Hot Stamp Wire Marking Concerns for Aerospace Vehicle Applications
ARP5369 Guidelines for Wire Identification Marking Using the Hot Stamp Process
ARP4404 Aircraft Electrical Installations
EUROPEAN NORMS.
EN 34375 Aerospace Series – Cables, Electrical, Aircraft Use (http://en-standards.standardsdirect.org/EN-Sheet124_list_48.html)
prEN 2853 Current Ratings for Electrical Cables to be Installed on Aircraft (in development)
prEN 3197 Aerospace Series – Installation of Aircraft Electrical and Optical Interconnection Systems (in development)
OTHER DOCUMENTS.
RTCA DO-160 Environmental Conditions and Test Procedures for Airborne Equipment (http://www.rtca.org/downloads/DEC%202004%20-%2005-01-
06.htm#_Toc92863870)
Eurocae ED-14 Environmental Conditions and Test Procedures for Airborne Equipment (http://www.eurocae.org/cgibin/home.pl?Target=va/documents/documents_general.html&Num =4)
International Organization for Standardization Document ISO 2574 Aircraft –Electrical Cables – Identification Marking http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnu mber=7536&ICS1=1&ICS2=70)
A-4
Appendix B
APPENDIX B NPRM PART 25 SUBPART H AND APPENDIX H DISCUSSION
Following are the discussions of the Part 25, Subpart H and Appendix H requirements published in the Federal Register on October 6, 2005, (70 FR 58508) in Notice of Proposed Rulemaking No 05-08, Enhanced Airworthiness Program for Airplane Systems/Fuel Tank Safety (EAPAS/FTS), at the time these rules were proposed.
NOTE: Some of the section numbers of the final rule are different than those proposed in the NPRM. Most of the proposed advisory circulars (AC) have been given final numbers. For ease of reference, the proposed section numbers have been replaced with the final section numbers, and the proposed ACs are identified with their final numbers, when available.
Other than that, no other changes have been made to the preamble discussion that follows.
Part 25 Subpart H—Electrical Wiring Interconnection Systems (EWIS)
The proposed subpart H consists of relocated, revised, and new regulations about EWIS. Unless we say otherwise, our purpose in moving requirements to subpart H is to ensure their application to EWIS. We do not intend to change their legal effect in any other way.
Section 25.1701 Definition.
Proposed § 25.1701 would define what constitutes an EWIS for the purposes of complying with the proposed subpart H requirements and other EWIS-related requirements of parts 25, 121, and 129.
Current regulations do not provide a definition of a wiring system. Without this definition, the proposed rules could be inconsistently applied to various wire-related components. To completely address the safety issues associated with wiring systems, requirements must address not only the wiring itself, but also components and devices that are required to adequately install and identify each wire. Various components and devices needed to route and identify wires are critical in ensuring that a proper electrical interconnection is made and maintained.
For the purposes of this NPRM, the term “wire” means bare and/or insulated wire used for the purpose of electrical energy transmission, grounding, or bonding. This includes electrical cables, coaxial cables, ribbon cables, power feeders, and databuses.
B-1
Appendix B
A proper electrical interconnection between two or more points requires more than just wire. Making the connection in a manner that ensures both functionality and safety requires various types of components, of which wire is one. Therefore, a clear definition of an electrical interconnection is necessary. The proposed regulation provides this and at the same time introduces the term “electrical wiring interconnection system (EWIS)” to describe that interconnection. The term EWIS means any wire, wiring device, or combination of these, including termination devices, installed in the airplane for transmitting electrical energy between two or more termination points. The proposed regulation expands on this basic statement to clearly identify which wire-related components are included in the EWIS definition and which are not. Most wires are routed with other wires that make up wire bundles and cable assemblies (or “looms,” as they are sometimes called). A single wire may also be routed separately. The same definition of an EWIS is applied to a single wire or to a bundle containing hundreds of wires.
To complete an electrical connection, various types of connectors are necessary. Examples are MS connectors (MS means military specification), D-subminiature connectors, and rack and panel connectors. Any connector used to complete an electrical connection is included in the EWIS definition. The exception to this is the mating connection on those devices that are excluded from the proposed definition. The excepted devices are addressed later in this discussion.
Connector accessories fall under the definition of EWIS. Such accessories include, but are not limited to, backshells, strain reliefs, grommets, and sealing plugs. Electrical connections to devices such as relays, interrupters, switches, contactors, terminal blocks, and feed-through connectors are parts of an EWIS. For example, the connection device on a relay is considered part of the EWIS, but the relay mechanism is not, because it is a termination point. A splice can be considered an electrical connector because it performs the same role as other connection devices by providing an electrical connection between two or more wires. The failure of a splice or relay connection could create a hazardous situation by exposing bare conductors or impairing system functionality.
Although a bus bar is not a “connector” in the traditional sense, it is a collector and distribution device for electrical energy and thus must be treated as part of an EWIS.
B-2
Appendix B Wire or wire bundles require devices to physically route and support them, such as clamps, brackets, standoffs, and other such components. These are included in the EWIS definition. Cable ties are included because they are used to hold multiple wires together and in place. The failure of one or more of these EWIS components could affect the ability of the wire to perform its intended function.
It could cause collateral damage to other wires in the same or adjacent bundles or cause the bundle to fail in a way that would cause structural damage or ignite flammable material, fluid, or vapors in the area.
Some wires must pass through pressure bulkheads, so a pressure seal is needed. Failure of a pressure seal could cause damage to the wires in the wire bundle and affect the functioning of the system they support. Some wire bundles use shields or braids to protect them from electromagnetic radiation, lightning, abrasion, and other types of physical damage. Failure of the shields or braid could cause, or allow, the wires to be damaged. It could also allow unwanted electrical energy to be coupled into systems and cause system malfunction. Thus, shields, braids, and pressure seals must be considered part of the EWIS and treated as such.
Sometimes adequate physical separation distance is not possible, and some sort of protective sleeving may be used. Since the sleeving is used to achieve separation, it must be considered part of the EWIS.
Conduits are included in the proposal because they are used to provide protection for wires as well as provide physical separation.
Conduits that have electrical termination for bonding are considered part of an EWIS because the failure of the bonding could create a hazardous situation.
The definition of an EWIS includes labels or other means used for identification. This supports the proposed § 25.1711 requiring new identification criteria for wires and other EWIS components.
Discussion of the proposed labeling requirements appears under the heading for § 25.1711.
The proposed regulation does not cover portable, carry-on, or other electrical equipment not certified for installation on the airplane under part 25. Examples of items not included are laptop computers and portable audio and/or video or other consumer devices typically carried on-board by passengers for personal use.
Increasingly, flight and cabin crew are using laptop computers in the performance of their duties. As stated, laptops are not part of the B-3
Appendix B EWIS definition, but any electrical connection used to support power and/or signal transmission that is part of the airplane TC, and that is used for the laptop or other carry-on items, is covered by the proposed definition.
The proposed EWIS definition does not cover fiber optic cable because fiber optic cable does not transmit electrical energy. But since fiber optics can provide functions (for example, data transmission) similar to those provided by wire, it is being expressly eliminated from the EWIS definition to avoid confusion.
The proposed definition excludes electrical wiring interconnection system components inside avionics equipment (highfrequency communication radio or flight data recorder, for instance), or the mating electrical connectors mounted on that equipment.
Such equipment is produced by various manufacturers for use on a broad range of airplane models and is designed and built to various performance and environmental specifications. Environmental testing, either by means of RTCA (Radio Technical Commission for Aeronautics) Document No. RTCA DO-160, EUROCAE 55 specification (specification of the European Organization for Civil Aviation Equipment), or other environmental qualification procedures approved by the FAA, ensures that the EWIS contained within avionics equipment is robust and well suited for the airborne environments in which it will be operated.
This proposal also does not apply to miscellaneous electrical equipment if that equipment has been adequately qualified to environmental conditions and testing procedures approved by the FAA, unless that equipment is specifically included in the proposed § 25.1701 as discussed in the following paragraph.
The definition of EWIS includes electrical wiring interconnection system components inside shelves, panels, racks, junction boxes, distribution panels, back-planes of equipment racks including circuit board back-planes, and wire integration units. We have included the components in this type of equipment because it, unlike avionics equipment, is typically designed and made for a particular airplane model or series of models. The same requirements that apply to airplane EWIS components must also be applied to the components inside that equipment. Avionics components must be sent back to their manufacturer or a specialized repair shop for service. But this type of equipment is maintained, repaired, and modified by the same personnel who maintain, repair, and modify the EWIS in the rest of the airplane. In an electrical distribution panel system, for example, separation must be designed and maintained within the panel just as B-4