Product Focus: Wire & Cable: The Long-Awaited NPRM

After more than five years of working group meetings, research and reports, the Federal Aviation Administration (FAA) finally announced in early May its intent to issue the long-awaited notice of proposed rulemaking (NPRM) for electrical wiring in aircraft — all 160 pages of it — early next year. That’s a large proposed rule, but it covers both design and operations, including wire inspection, maintenance and technician training. It also calls for each commercial airframe manufacturer to have an electrical standard wire practices manual (ESWPM) accompanying each aircraft that rolls off its assembly line. The NPRM proposes both revisions to requirements outlined in Part 25, covering factory installation of wire and cable, and new requirements to incorporate in Part 25, designated Subpart H. The changes will apply to all future Part 25 type certificates (TCs) and supplemental type certificates (STCs).

It wasn’t just its length and inclusiveness that made the NPRM a long time coming, however. The aircraft certification and flight standards personnel in FAA’s "Tiger Team" for aging aircraft rulemaking have sought to coordinate all new rules applying to the maintenance of aging aircraft. The proposed wire and cable rule, therefore, is to be enacted in tandem with other maintenance and repair regulations, covering such areas as structural fatigue, corrosion prevention, fuel tank maintenance and an enhanced structural repair inspection process.

FAA also has taken the time to ensure that the proposed wire and cable regulation harmonizes with regulatory activity in Europe and Brazil, accounting for the geographic sources of most commercial aircraft. FAA approval of tasks resulting from new manufacturer safety analyses is to be granted prior to start of the operator compliance period for incorporating the new tasks. Also there was delay because of the enormity of the recommendation package, which forced detailed cost-benefit analysis to determine which parts of the package should be mandated and which should remain voluntary.

The NPRM will be issued for comment in early 2005. Few snags are expected during the NPRM comment period because of industry input throughout the proposed rule’s development and because many advisory circulars (ACs) covering much of the NPRM’s content will be issued concurrently and are already available for public inspection. FAA plans to have the rule enacted in mid-2006.

Currently, the NPRM applies to aircraft that carry 30 or more passengers or a 7,500-pound (3,400-kg) maximum payload or more. However, the Aging Transport Systems Rulemaking Advisory Committee (ATSRAC), a government-industry task force that has supported FAA in the NPRM’s preparation, is now investigating whether wire and cable regulation should be applied to aircraft bearing six to 29 passengers, as well, according to Kent Hollinger, ATSRAC chairman.

FAA published an overview of the NPRM on the Federal Register in May. This gives operators and manufacturers advanced notice of the proposed rule’s contents. Background details of the research conducted by 13 ATSRAC working groups in support of the NPRM, along with the proposed rule and ACs, can be found at www.mitrecaasd.org/atsrac

Generally, the NPRM elevates the status of wire and cable to that of a system, which means it can no longer be viewed as "fit and forget," says Hollinger. Wire and cable, therefore, will be subject to dedicated inspection schedules and procedures. Maintenance procedures will include enhanced zonal analysis procedures (EZAP), which will more precisely define the inspections and intervals needed to ensure the continuing safe operation of the electrical wiring interconnection system (EWIS). These new procedures will be established by TC and STC holders for operators to adopt in their maintenance programs.

To minimize corrosion, the NPRM calls for specific guidelines from the TC and STC holders on how to wash areas of the aircraft housing wire and cable. These include everything from the water temperature and pressure to the cleaning solution’s pH level.

Part 25, Subpart H covers the many aspects of wire and cable installation by the original equipment manufacturers (OEMs), from materials selection to fire protection to wire labeling. A significant segment of Subpart H covers proper wire separation. It is to assure the isolation of wires and cables carrying heavy current, guarding against electrical interference and guaranteeing that the failure of one power source does not affect another power source or signal wire.

Most OEMs—Boeing, Airbus and Bombardier, for example—already have developed ESWPMs, in part to reduce the amount of verbiage in their other aircraft maintenance manuals. Hollinger says the ESWPMs that most OEMs already have produced will probably need "only minor modifications."

COMPANIES

A.E. Petsche Co. Inc. – www.aepetsche.com

AeroFlite Enterprises Inc. – www.aeroflite.com

Aircraft Engineering & Installation Services Inc. – www.aeisinc.com

AirWorks Inc. – www.airworksinc.com

Ametek Aerospace – www.ametek.com

Astro Industries – www.astro-ind.com

Chippewa Aerospace – Ph: 843-828-1160

Christensen Industries – www.christensenindustries.com

Cirris Systems Corp. – www.cirris.com

Dallas Avionics Inc. – www.dallasavionics.com

Data Bus Products – www.databusproducts.com