Business & GA, Commercial

Safety in Avionics: Wiring Safety: Progress or Procrastination?

By David Evans | February 1, 2001
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A White House task force report on aircraft wiring can be looked at two ways. One is that it stands as a promise of real progress. The other is that it represents a prescription for procrastination.

The report, issued Nov. 15, 2000, in the twilight hours of the Clinton Administration, affirmed many things that needed to be said. Indeed, given the rhetorical blandness typical of such blue ribbon efforts, the report of the Wire System Safety Interagency Working Group was unusually blunt. Here’s a sampling:

  • "While there is a tendency to ignore wire systems, there is a pervasive need to manage aging wire systems so that they continue to function safely."

  • "Faulty wire systems pose a risk to public…safety; (they) may lead to failure of essential functions and even to smoke and fire. A recent study of Air Force aircraft mishaps or accidents related to electronics revealed that 43 percent of them were related to the wiring interconnection system."

  • "Wire systems maintenance is very expensive, and the lack of access to detailed wiring maintenance data has historically limited funding for maintenance or modification unless a major system breakdown occurs."

  • "Wiring is often treated as a ‘fit and forget’ commodity rather than as an indispensable system. A significant cultural shift is necessary to ensure that wire systems be designed, installed and maintained for long-term integrity."

That’s a taste. Good words. The task force recommends a broad-front research effort to develop improved inspection, maintenance and circuit protection technologies. Therein lies the promise of real progress.

There’s a dark side. For operators, research of a solution out on the far horizon can lead to delay. Defer costly wire maintenance today, because tomorrow’s technology can mute the burdensome cost so somberly cited in the task force report.

The Golden Solution

One of the centerpieces of the task force’s research program is the development of arc fault circuit interrupter (AFCI) technology. These breakers, similar to their larger brethren found in residences throughout the country, can cut or interrupt a spike in the current before it develops into the lightning bolt of a full-blown arc. The challenge is to shrink cigarette pack-size AFCI breakers designed for home use into a package about a tenth that size, suitable for use in aircraft circuit breaker panels. Further, the false trip rate has to be minimized. That is a much greater challenge for aircraft application than for residences. An AFCI in an aircraft must be able to reliably detect at least four kinds of faults, each of which presents a unique electronic "signature" as it were. There is your dry arc fault, your wet arc fault, your ticking fault, and a variant, the so-called "teased" fault.

Those engaged in developing AFCI technology are acutely aware of the challenge–to trip when circuits go bad, and to not trip under related circumstances, such as electromagnetic interference (EMI). Bob Ernst, head of the Navy’s Aging Aircraft Integrated Product Team, put the matter succinctly and colorfully: "If your wingman turns on his radar or makes a radio transmission, you don’t want all your circuit breakers to pop because they interpreted those signals as arc faults."

The AFCI must be able to reliably identify the various types of wiring faults–otherwise the false trip rate will severely erode confidence in its functioning, possibly tempting pilots to reset breakers. In short, the technical challenges are not trivial. The U.S. Federal Aviation Administration (FAA) is putting substantial fiscal and institutional support into a collaborative effort with industry and the U.S. Navy to develop AFCI technology. And, whenever media reports surface of multiple cracks in aircraft wiring, FAA officials step forth to assure the public by hailing the heady promise of AFCI devices to blunt the threat.

The "silver bullet" approach is appealing. Retrofit phalanxes of AFCIs into the breaker panels of the passenger-carrying fleet, and the need for potentially costly wire maintenance is much diminished.

Procrastinators Anonymous

Unquestionably, AFCI technology is worth pursuing. On the other hand, holding forth this technology as the great hope can be a prescription for inaction. Operators do not have that luxury.

When an AFCI device trips, one does not know if the fault was real, what kind it was, or where it occurred. AFCI technology, in all its promised wonderfulness, does not obviate the need for what might be called a Wire Integrity Program. Yet the White House task force report may be abetting the notion that operators should wait for tomorrow’s technology. The report declares that today’s wiring inspection technology can only detect "hard failures," not slight deterioration such as chafing. If that demonstrably untrue statement is allowed to stand unchallenged, then the subliminal message is that operators may as well wait for the advent of improved inspection technology.

To be sure, there is no single piece of equipment or methodology capable of satisfying all test requirements. But, as wire ages in service, anomalies can be detected short of complete loss of function. This is not an advertisement, but a number of companies have banded together to offer a Wire Integrity Program. "The premise behind a Wire Integrity Program is that every wire in an aircraft should be included in a test program from the day it is delivered to the day it is retired," declared Mark Brown of GRC International Inc. His company is one of six offering a package of testing techniques that can be tailored to an operator’s needs. Customers can decide upon the scope of their testing, and which wires are to be assessed. For example, testing could be restricted to flight-critical wires, and to wires located in known areas of high wear (wheel wells, exposed flap/slat areas on the wing, etc.).


The Navy found that its maintenance budget was being gobbled up by the high cost of unscheduled wire maintenance activity. It put a wire husbandry program in place, saved a bundled of money and increased the mission-capable rate of its airplanes. For commercial operators, the Navy’s demonstrated success implies higher dispatch reliability at less cost.

That’s what can be done now. Not tomorrow. That’s with today’s admittedly imperfect techniques and technology. And, in this day of greater liability exposure to those operators who cannot demonstrate "the highest standard of care," a few questions are proposed. Just as built-in test (BIT) technology is used to assess the functioning of avionics components, operators might consider these questions as a form of self-test about wiring husbandry:

  • Do you have a wire management or wire integrity program?

  • Do you know what inspection techniques are being used to assess the condition of your wiring systems, wire insulation and wire installation?

  • Do you know how many in-flight smoke or fire events have been experienced?

  • Do you know the number of unscheduled landings resulting from in-flight smoke or fire events?

  • Do you know the number of incidents of burned, charred or damaged wiring that have been discovered during the course of your maintenance activity?

  • Do you know the amount of lost revenue that has been identified with respect to wiring problems?

  • Do you know the percent of your maintenance budget associated with trouble-shooting and repairing wiring problems?

On the basis of the answers, this scoring is suggested:

  • "Yes" to one to two questions and "No" on the remaining: Could be living in ignorance.

  • "Yes" to three to five questions: The beginning of awareness.

  • "Yes" to six to seven questions: Full awareness with a program to match.

For those tempted to wait until the vaunted AFCI technology is refined, a word of caution. The breaker trips after a fault occurs. A Wire Integrity Program can help prevent wiring-related faults before they occur. The difference in approach is profound: triage, or trying to prevent.

David Evans is editor of the award-winning newsletter Air Safety Week. Comments should be directed to [email protected].

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