Reader Feedback

Wiring Implications

Your excellent coverage of the recent NPRM (Notice of Proposed Rulemaking) on wiring inspections (AM, March, p. 24) highlighted most of the important aspects of this new rulemaking effort, but I would like to point out a few more unique features.

To my knowledge, this is the FAA's first attempt to mandate approved Instructions for Continued Airworthiness (ICA) via the FARs (proposed Part 25 Subpart I). ICAs have historically been merely accepted by the FAA, even though SFAR88 did break the ground for approved instructions. Also, by making increased use of FAR 25.2, the FAA proposes to make Subpart I retroactively applicable to existing Type Certificates, something that had previously been handled through SFARs.

Declaring wiring to be a system (Proposed Part 25 Subpart H) is more than just nomenclature. The major impact of this change will be the analysis of the aircraft Electrical Wiring Interconnection System (EWIS) from a system safety viewpoint, including the effects of a physical failure of the wiring. Too often in the past, a wiring failure was viewed only in light of the loss of function of the system that it supports, without consideration given to possible damage to other aircraft systems or areas due to arcing, fire, etc. The associated draft Advisory Circular 25.17xx describes this in more detail.

The Aging Transport Systems Rulemaking Advisory Committee (ATSRAC) discovered that "aging" was not defined solely by the calendar, but rather "includes the breakdown of inherent characteristics of wire as a function of time and the effect of maintenance, contamination, improper repair, modification, and mechanical damage" (Task 6 Final Report). Our aircraft inspections found relatively new airplanes with inadequate wiring conditions, while some much older airplanes exhibited good overall wiring health. For this reason, I urge all operators and maintenance facilities to voluntarily adopt an EWIS Training Program based upon draft Advisory Circular 120-YY.

With the proposed enhanced design practices, and adoption of best-practice maintenance procedures, aircraft wiring should be able to safely and satisfactorily perform its intended function for the life of the aircraft, negating the need for rewiring as suggested in your article.

Kent Hollinger
ATSRAC Chairman

Human Factors

I just received a copy of the May issue of AM and was delighted to see that the editor highlighted some recent FAA work in the area of Maintenance Human Factors (AM, May, p. 4).

As was pointed out, the FAA has produced a 2007 pocket calendar, which features one of the Dirty Dozen each month. It is our goal to have these calendars end up in the shirt pockets and toolboxes of as many technicians as possible prior to the start of the 2007-year to help raise the awareness of Maintenance Human Factors issues.

These pocket calendars are now available at the local FSDO (Flight Standards District Office) through your Federal Aviation Administration Safety Team (FAAST). We will also have them available at certain air shows, conferences, symposiums, workshops, etc., from now through the end of the year.

Jay Hiles
Aviation Safety Inspector, Maintenance Human Factors
Air Carrier Maintenance Branch, Federal Aviation Administration