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Proposed Advisory Circular 25-YY, “Development of Standard Wiring Practices Documentation”

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Information about this document as published in the Federal Register.

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Federal Aviation Administration (FAA), DOT.


Notice of availability and request for comments.


This notice announces the availability of and requests comments on a proposed advisory circular (AC) that sets forth acceptable methods of compliance with section H25.5(a)(2) of Appendix H to 14 CFR part 25 concerning development of an electrical system standard wiring practices document. This proposed AC complements revisions to the airworthiness standards that are being proposed by a separate notice. This notice is necessary to give all interested persons an opportunity to present their views on the proposed AC.


Comments must be received on or before December 5, 2005.


Send all comments on the proposed AC to: Federal Aviation Administration, Attention: Stephen Slotte, ANM-111, Airplane & Flight Crew Interface, Federal Aviation Administration, 1601 Lind Avenue SW., Renton, WA 98055-4056; telephone (425) 227-2315; facsimile (425) 227-1320, e-mail Comments may be inspected at the above address between 7:30 a.m. and 4 p.m. weekdays, except Federal holidays.

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Annette Kovite, Transport Standards Staff, at the address above, telephone (425) 227-1262.

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Comments Invited

Interested persons are invited to comment on the proposed AC by submitting such written data, views, or arguments as they may desire. Commenters should identify AC 25-YY and submit comments, in duplicate, to the address specified above. All communications received on or before the closing date for comments will be considered by the FAA before issuing the final AC. The proposed AC can be found and downloaded from the Internet at​rgl under “Draft Advisory Circulars.” A paper copy of the proposed AC may be obtained by contacting the person named above under the caption FOR FURTHER INFORMATION CONTACT.


This proposed AC provides guidance for demonstrating compliance with the transport category airplane certification requirements of H25.5 Electrical Wiring Interconnection System (EWIS) Instructions for Continued Airworthiness. The guidance provided in this proposed AC is applicable to all air carriers, air operators, holders of type certificates, holders of STCs, maintenance providers, and repair stations operating under 14 CFR parts 21, 25, 43, 91, 121, 125, 135, and 145.

This guidance is a product of the Aging Non-Structural Systems Plan. The FAA developed the Aging Non-Structural Systems Plan to address recommendations of the White House Commission on Aviation Safety and Security (WHCSS). That commission recommended that, in cooperation with airlines and manufacturers, the FAA's Aging Aircraft Program should be expanded to cover nonstructural systems.

The commission was concerned that existing directives, procedures, quality assurance, and inspections may not be sufficient to prevent safety-related problems caused by corrosion and other deteriorating effects on nonstructural components of commercial aircraft as they age. To fully address the WHCSS recommendations on aging systems, we Start Printed Page 58563formed an Aging Nonstructural Systems study team. This team, led by the Transport Airplane Directorate (TAD), conducted an inspection of systems in several aging airplanes. It then met with FAA principal maintenance inspectors (PMI) tasked with oversight of major air carriers to evaluate the need for additional work in addressing the commission's concerns. The team concluded that additional work was warranted and that industry involvement in this work was essential.

The elements of the Aging Nonstructural Systems Plan were grouped into five major tasks. One task was to define standards for a simplified chapter 20, commonly referred to as the standard wiring practices manual (SWPM), of manufacturers' airplane maintenance manuals, and to define a process for training development based on the airline's customized chapter 20. This task was assigned to industry-represented Task 4 Working Group.

The tasking statement assigned to the Task 4 Working Group also required the group to consider “simplification” of chapter 20 of wiring diagram manuals (WDM). The working group concluded that simplification of the chapter 20 SWPM by end users was not appropriate for several reasons:

1. It would not be practical, because end-users do not have access to the source data.

2. It would result in different standards from one end-user to another.

3. End-users would need the details for inspection, maintenance, and repair that are currently in the manufacturer's SWPM.

At the conclusion of Aging Transport Non-Structural Systems Plan Phase I, the Task 4 Working Group stated that the current presentation and arrangement of standard wiring practices make it difficult for an aircraft maintenance technician to locate and extract pertinent and applicable data necessary to effect satisfactory electrical repairs.

Subsequent tasks assigned to the Standard Wire Practice Manual Harmonization Working Group required the development of a standardized SWPM format and a definition of the minimum content to be included in an SWPM.

This guidance presents one means, but not the only means, of complying with the part 25 revisions proposed in Notice No. 05-08, entitled “Enhanced Airworthiness Program for Airplane Systems/Fuel Tank Safety (EAPAS/FTS),” published in this same edition of the Federal Register. Issuance of AC 25-YY is contingent on final adoption of the proposed revisions to part 25.

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Issued in Washington, DC, on September 22, 2005.

John J. Hickey,

Director, Aircraft Certification Service.

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[FR Doc. 05-19409 Filed 10-5-05; 8:45 am]