A dozen advisory circulars (ACs) have been issued to help interpret and carry out the wiring inspections mandated by the FAA (see Significant Regulatory & Related Activity). One of the best written is AC No. 25-27, titled thoroughly, “Development of Transport Category Airplane Electrical Wiring Interconnection Systems [EWIS] Instructions for Continued Airworthiness Using an Enhanced Zonal Analysis Procedure” (the full 100-page AC may be viewed at the FAA website).

Despite its length, the AC is a model of clarity and, better yet, includes photographs of what must be examined by maintenance technicians (see figures A and B). As the AC says of the enhanced zonal inspection procedure (EZAP):

“The EZAP will allow the user to determine the appropriate general or detailed inspections that any cleaning tasks … needed to minimize the presence of combustible material.”

The whole idea is to maintain the EWIS in “airworthy condition” by scrapping the traditional maintenance philosophy of ignoring wiring and connectors unless a condition requires corrective maintenance (for example, a popped circuit breaker indicating a fault in the wiring); the new philosophy is a more proactive. As the AC says, a “Protect and Clean As You Go” philosophy now applies. To properly inspect for wiring chafing, broken clamps, sagging, drill shavings (swarf) and such, the wiring must be visible:

“The area to be inspected should be clean enough to minimize the possibility that collected dirt or grease, or other contaminants, might hide unsatisfactory conditions that would otherwise be obvious. … The cleaning process itself should not compromise the integrity of EWIS. Avoid using high pressure cleaning and abrasive materials that could damage wire insulation and other EWIS components.”

Eminently sensible advice. Lectromec, a wiring design and testing firm in Dulles, Va., in its January 2008 newsletter on the new requirements, stressed the sea-change involved in the new requirements: “They will require significant changes to certification and maintenance programs by all affected parties.” Given the increasing “electrification” of transport category airplanes, the new mandates may have been nine years in the making, but they come not a moment too soon.