Aircraft Wiring- It always Cracks

WASHINGTON, Sept 15 (Reuters) - All aircraft wiring ages, and it is not uncommon to find five to 10 insulation cracks per 1,000 feet of wire in active aircraft, a congressional subcommittee heard Wednesday.

Armin Bruning, an engineer who heads a company that has done testing for the National Transportation Safety Board, said the plastics insulating wire all aged, leading to problems ranging from minor troubles with instruments to

fires and sometimes deaths.

Wiring is becoming one of aviation's hottest safety topics, with a suspected role in two high-profile crashes in the last four years. There has also been increased research into the problem.

A Federal Aviation Administration official told a hearing of the House Transportation subcommittee that the so-called aging aircraft fleet would soon include heavily electronics-reliant aircraft of the 1980s such as the

Boeing (NYSE:BA - news) 757 and 767 and the Airbus A-300.

``The FAA and, indeed, the entire aviation industry are only now beginning to have a greater appreciation and understanding about the need to examine nonstructural aspects of our aircraft,'' FAA Associate Administrator Tom

McSweeny said.

Bruning, president of Lectromechanical Design Co., a Dulles, Virginia, concern that has worked with the U.S. Navy, said humidity, high temperatures and strain all contributed to wire aging.

Although not all insulation breaks lead to sparks or accidents, it is best to minimize the problem, he said.

TWA, SWISSAIR CRASHES

NTSB aviation safety director Bernard Loeb said the board's attention had been focused by two major crashes: the 1996 explosion of a TWA jumbo jet off Long Island, which killed all 230 people on board, and last year's Swissair

MD-11 crash off Canada's Nova Scotia coast, which killed the 229 people it carried.

Safety investigators suspect that an electrical fault, possibly in the fuel measuring system, ignited fumes in the center fuel tank of TWA Flight 800.

In the Canadian crash, attention has focused on damaged wires in the ceiling of the cockpit.

Loeb said inspections of more than 25 other aircraft after TWA 800 found wiring problems in all cases, ranging from lint and metal shavings on wire bundles to cracks in insulation.

The NTSB is following up with tests in which wire bundles contaminated with metal drill shavings are vibrated.

It was recently reported that another series of tests documenting the arcing potential of TWA 800-type wire when contaminated with galley fluids and lavatory waste showed surprisingly violent reactions.

Loeb said outside the hearing that the NTSB was also planning to use an operating Boeing 747 to check the effect of turning powerful electrical circuits on and off and the induction of strong currents into adjacent low-voltage wires.

Under one scenario, excessive electrical energy may have entered TWA 800's fuel tank through the normally low-voltage fuel measuring system.

``The safety board is concerned that industry and regulatory efforts have been relatively ineffective in preventing the types of wiring hazards seen during the TWA Flight 800 investigation,'' Loeb testified.

September 15, 1999 -

Pilots Union Calls For Additional Research on Aircraft Wiring

WASHINGTON (USA) - The Air Line Pilots Association, International (ALPA)
today told Congress that it is time to re-examine the assumptions and practices on aircraft electrical wiring. "Various events and accidents have made it imperative that we examine all aspects of aircraft wiring, from the design characteristics, to the materials used, to how they are installed in the aircraft. We also must revise our previous notions of how well wiring holds up under aging and use. And wherever possible, we must pursue technological improvements that provide better alternatives to electrical wiring," said Captain Paul McCarthy, executive air safety chairman for ALPA.

McCarthy was testifying at hearings of the House Subcommittee on Oversight, Investigations and Emergency Management, part of the Committee on Transportation and Infrastructure. The subject was aircraft wiring, and McCarthy was careful to separate ALPA's testimony from any ongoing accident investigations.

"Although the subject of aircraft wiring has been a central part of at least two recent airline accidents, I wish to make it clear that nothing I say here should be construed as being directed at any of these specific investigations. Rather, they should be taken as general comments on this aspect of aviation safety. I also want to make it clear that we at ALPA are not trying to issue any sort of general alarm about wiring concerns. Our members continue to operate these airliners, including the older models, with abundant confidence in their airworthiness," he said.

McCarthy addressed several types of failures and concerns with aging wiring, including "ticking faults," "wet wire" fires (a form of the ticking fault now known as "wet arc tracking"), the effects of vibration, moisture, heat and physical installation stresses, and the use of polyimide or Kapton as a wiring insulator. ALPA urged a five-part solution: improve the Federal Aviation Regulations standards, revamp design and installation processes, incorporate modular construction, use fiber optics where appropriate, and evaluate other potential methods of signal transmission, such as infrared and FM radio. ALPA is the oldest and largest pilot union in North America. It represents 55,000 airline pilots at 53 carriers in the U.S. and Canada.(The full text will be posted at ALPA's Web site, www.alpa.org.)

11:57 AM ET 09/14/99

Focus of TWA 800 crash on wiring - NTSB

WASHINGTON, Sept 14 (Reuters) - National Transportation
Safety Board (NTSB) investigators are focusing on possible
sparking from aging wires as the cause of the 1996 TWA Flight
800 crash off Long Island that killed all 230 people on board.
James Hall, chairman of the NTSB, told NBC's Today Show
that testing of wiring bundles in 25 different planes has
focused U.S. aviation officials' attention on Boeing
747's electrical system as a possible cause of the accident.
"We are now looking very closely at possible electrical
discharges that may have come off of some of that wiring that
could have caused the accident itself," Hall said.
NTSB investigators have long suspected that fumes in the
plane's center fuel tank were ignited by some sort of electrical fault.
Hall was speaking from Calverton, Long Island, where the
reconstructed wreckage of TWA 800 was being moved to a smaller
hangar Tuesday.
On Monday, USA Today reported that the private laboratory
hired by the NTSB to test Poly-X wiring -- the same type used
in the destroyed TWA 747 aircraft -- found that it sparked more
than expected when bundles of it were wet-tested.
Wet-testing simulates what might happen when cracked
insulation on electrical wires is exposed to salt water or
waste water from an airplane's galley or restrooms.
For his part, NTSB chairman Hall refused to confirm those
results during his NBC News interview, deferring any comment
until the safety board's final report is released.
That report is expected early next year.

Hazard Posed by Bad Aircraft Wiring Under Congressional Scrutiny

Aircraft wiring is taking on an importance equal to that devoted for some years now to aging aircraft structures. In fact, the suspected parlous state of wiring throughout the U.S. airline fleet has triggered the first known Congressional hearing devoted specifically to the subject.

Operators could be faced with political pressure to replace wire and install new, high-tech circuit breakers capable of detecting electrical faults.

Last week the House Transportation and Infrastructure Oversight Subcommittee took testimony from half a dozen witnesses on the general subject of aircraft electrical system safety.

Rep. Tillie Fowler (R-Fla.), the subcommittee chairwoman, set the tone by asserting at the outset, "Old and damaged aircraft wiring may be one of the weakest links in aviation safety."

Indeed, wire failures may pose a greater hazard than hydraulic system failures. Since critical flight controls are at stake, hydraulic systems have triple or quadruple redundancy. Electrical systems, though, may be just as critical given the greater dependence of modern transports such as the MD-11 and B777 on electrically powered systems and controls. Whereas hydraulic faults tend to be more self-evident, the outcome of an arc-tracking incident or electrical fire can quickly lead to systemic confusion, fire, smoke and potential pilot incapacitation.

The National Transportation Safety Board (NTSB) has documented at least 15 cases where electrical wiring malfunctions were involved an aircraft incidents and accidents. Yet there seems to be a generalized reluctance to face the implications. According to Dr. Bernard Loeb, director of the NTSB's aviation safety office, the Board's ongoing investigation into the TWA Flight 800 disaster and the Swissair Flight 111 in-flight fire and other recent incidents have "changed the way the industry looks at electrical wiring."

However, Loeb went on to say, "We are concerned. The industry seems to be defining what were are seeing as not very significant."

"We need to address this issue of aging systems and wire," he urged.

Indeed, Safety Board inspections of some two dozen airplanes provide powerful evidence that the wiring deficiencies found on the TWA Flight 800 accident aircraft were not an anomaly, but perhaps more representative of the general state of wiring in the fleet). Even new aircraft may be leaving the factory with problems, as evidenced by the discovery of metal shavings found in wire bundles on brand now aircraft. Over time, those metal shavings can "saw" through wire insulation, exposing conductor and creating the opening for dangerous arcing.

Richard Healing, director of the U.S. Navy's safety and survivability programs, described how the Navy shifted from wire types such as aromatic polyimide, or Kapton, replacing it with a type of wire known as cross-linked ethylene-tetrafluorethylene (XL-ETFE). Although its cut-through, scrape abrasion and smoke characteristics are less desirable, it has become the Navy's preferred wire choice for many aircraft applications because it is a homogenous material throughout the thickness of the insulation, and its plastic characteristics eliminate problems with longitudinal cracking and topcoat flaking.

Retrofitted as part of a comprehensive Navy-wide aircraft wire management program, Healing said the effort, "while not perfect," has been "about 88% effective in reducing risk and eliminating wire insulation-related problems."

Newer, composite wire types -- for example one type that goes by the trade name Tensolite -- provide significantly better arc, flammability and smoke resistance than XL-ETFE. Less than 20 percent of the U.S. fleet is flying with such wiring. One reason may be its greater cost. According to Mark Roberson, representing the Tensolite Company of St. Augustine, Fla., an aircraft costing $35 million will contain about $3,500 worth of his company's composite wire type, as compared to an estimated cost of $2,800 to install non-composite wire in the aircraft -- a $700 difference.

The Navy's success prompted Rep. James Traficant (D-Ohio) to bluntly suggest a similar program for the airline industry. "The Congress wants all faulty wiring to be repaired and replaced, and (to see) that monitoring is diligent," he declared.

In addition to fitting aircraft with newer, safer wire types, witnesses discussed the potential of arc-fault detection circuit breakers -- downsized variants of arc-fault circuit interrupters (AFCI's) finding their way into residential circuit breaker panels.

Capt. Paul McCarthy, executive air safety chairman of the Air Line Pilots Association (ALPA), said flatly, "The circuit breakers we have in the cockpit will not protect" against arcing events where the temperature of the wire does not get to a threshold sufficient to trip the breaker.

While AFCI breakers hold great promise, their development to the point of reliable performance is not a trivial issue, asserted Dr. Armin Bruning. The president of a Sterling, Va.-based wire testing company, Lectromec, Bruning explained that each of the four types of arcing presents a unique "signature." The AFCI breakers would have to be capable of reliably detecting each of the signatures).

The transition from household to aircraft use is years away.

Above all, McCarthy declared, regulations regarding aircraft wiring, unchanged for two decades, need to be brought up to date. He offered five "really quite simple" recommendations:

1. Enhance FAR 25.1353 and AC 43.13. Considering the expansion in the quantity and complexity of electrical devices on today's aircraft, and the resultant amount of wire, existing regulatory guidance does not adequately address the current technologies and practices.

2. Revamp design and installation practices. Specific areas to be addressed should include power sources, intermixing of insulation types in the same wire bundle, fastener design and bundling methods.

3. Incorporate modular construction. Modular wiring, McCarthy suggested, would allow for ease of replacement on a scheduled basis.

4. Evaluate/incorporate fiber optics. Aircraft entertainment systems, running 115v power into seats, and interior lighting, "seem two good candidates for this type of technology," McCarthy said.

5. Evaluate alternative signal transmission methods. Infrared (IR) and frequency modulated (FM) radio technology used in other industries should be considered for aviation use as well.