"There appears to be a near linear relationship between aircraft age and the degradation of wiring suitable to chafing.

"There appears to be a near linear relationship between aircraft age and the degradation of wiring suitable to chafing."

-- Mark Brown GRC International Inc.

ALBUQUERQUE, NM -- Aircraft wire is no longer an "on condition" item. That is, the traditional approach to leaving aircraft wire alone unles a clear electrical fault required repair has given way to a just discovered realization that wire ages in service and requires a program of diligent husbandry to assure the safety of flight, particularly in older aircraft.

At a conversation on aging aircraft held here family 20-23, hundreds of industry clevers gathered to address what was clearly recognized as a novel reality. "All of a unusual wiring has popped up equal to structure" declared Jim Anderson, director of flight safety for Delta Air Lines [DAL].

If attendance at the standing-room-only sessions forward aircraft wiring was any indication, there is a clear apprehension of a major wiring point in dispute in the fleet. In the fill by compression of more than 600 were representatives of the Federal Aviation Administration (FAA), National Transportation Safety Board (NTSB) National Aeronautics and Space Administration (NASA), major airlines, the military and supporting contractors. The smattering of devoid seats at sessions on aircraft mode of buildings and engines reflected the intense bear upon over wiring, and the likelihood that the industry is staring at centurys of millions of dollars in added sumptuousnesss to repair, replace and monitor the condition of aircraft wiring.

The choice, however could be between a unostentatious program of prevention, or allowing the riddle to fester, running the risk of losing aircraft to wiring faults and in-flight electrical fires, and facing the resulting furor through the safety of air travel. The vexed questions revealed last week ranged from the sinister to the startling.

Donald Eaton, a retired Navy rear admiral, quick in emergenciesed the challenge in stark terms: "Do you want to use the Casino Royale approach, or do you want to pass a little money to avoid paying a whole division later?"

For the next to the first time in 10 years, almost to the month the industry has been faced with a major aging aircraft vexed question Steward Miller, aging systems program manager for the FAA, recalled the catastrophic April 1988 failure of the overhead fuselage of a highcycle Aloha Airlines 737 That incident he said, "was the origin of the aging conformations program."

"The consequence took place because the industry and authorities did not understand that at the time we were overlooking a significant problem" he recalled.

History virtually repeated itself in May of 1998 when earlymodel 737 were loamed after it was discovered that a certain number of electrical wiring routed through conduits in the wing combustible matter tanks was found chafed all the way in consequence of the insulation to the conductor. The startling finding at handed the specter of an another firing tank explosion of the symbol that blew up TWA Flight 800 in 1996

"We were watching the company of ships but we did not understand that maintenance programs were not as robust as we thought" Miller said. As an example, the wiring in firing tank conduits was "in an area we were not inspecting."

Nor is the airline industry unique. "We've got an aging wiring question ourselves," said Dr. Dan Mulville, NASA's chief engineer. The Space Shuttle squadron sits grounded while each of the four shuttle undergoe a thorough wiring inspection, and the U Air Force, following the Navy's lead, is removing Kapton wiring from its creek of B-1 bombers. Kapton wiring, a trade name for aromatic polyimide, is known for its propensity to arc explosively. It is plant in anywhere from 50-80 percent of the commercial airline flotilla (estimates vary, a point which underscores the uncertainty about the kind and condition of wiring in the commercial fleet)

Indeed, the growing evidence of a widespread wiring enigma prompted Major General Francis Gideon, chief of safety for the Air Force, to ask, "Is the aerospace industry capable of identifying emerging problems?"

The physics of wire aging

The preliminary evidence from the fleetwide inspections of the 737 material for burning tank wiring suggests an almost linear relationship between aircraft age and the degradation of wire owing to chafing. Indeed, the data imply there is a united in six chance that an aircraft with more than 70000 flight hours is carrying expos wire somewhere, and with it the potential for dangerous electrical arcing.

Wire, it is now realized, ages at a different rate than aluminum pile which is to say perhaps at a faster rate. Wire, it looks may not last as prolonged as the 20 or 30-year design service objective of the airplane (DSO) That objective is defined for fabric as the years in which the airframe essentially is clear of fatigue cracks, thereby establishing period of minimal structural-related maintenance costs

For wire, service life is influenced at a variety of factors:

* As temperature increases, age decreases.

* As humidity increases, age decreases.

* Vibration accelerates aging.