FAA Wants More Focus On Aircraft Wiring

Monday October 10, 2005

October 9, 2005

US aviation regulators want the industry to pay closer attention to aircraft wiring that could pose risks for electrical failure and fire, especially on older planes.

The Federal Aviation Administration last week proposed new maintenance, inspection and design standards that would require airlines and manufacturers to analyze

NEW RULE TARGETS EXPLOSIVE WIRING ISSUES
Almost ten years after an electrical fault is suspected to have caused the center tank of a TWA Boeing 747 to explode off New York (killing 230 people), the FAA has come up with a new set of proposed regulations aimed at ensuring (encouraging) airlines and manufacturers to better look after the lifeblood of their airplanes. The Notice of Proposed Rulemaking would essentially treat wiring as a separate system, rather than as part of the other systems, thus boosting inspection, maintenance and design requirements that the FAA claims will actually save the airlines money. "There will be more efficient planning of maintenance programs and less down time for aircraft," FAA spokesman Hank Price told reporters.

Instead of patching up wiring as needed, the new regimen would require more work to be done at fewer intervals. The changes will have a direct cost of $425 million over 25 years but Price said the efficiencies afforded will actually save the airlines $800 million. Besides the TWA flight, more than 400 wiring failures have been documented in airliners, including the downing of Swissair Flight 111 off Nova Scotia in 1998, which was believed to have been caused by overheated wiring in the plane's entertainment system.

aircraft wiring with the aim of making it more fire resistant and easier to pinpoint and correct problems.

Although aircraft design standards are rigorous, wiring is generally considered part of the components they power, like engines or cockpit controls. Maintenance inspections have never given wiring special attention as a separate system.

Current inspection requirements are too general and there is too little attention paid to the impact of how wiring modifications on one part of a plane might affect other parts of the same aircraft, the FAA said.

The new regulation, if adopted, would allow airlines to do more work on wiring at fewer intervals.

"There will be more efficient planning of maintenance programs and less down time for aircraft," said FAA spokesman Hank Price. "Instead of doing it (piecemeal) everyone will come under one umbrella."

The agency estimated the cost of the new program at USD$474 million over 25 years. But it said airlines should save nearly USD$800 million from retooled maintenance procedures and improved safety.

Between 1995-2002, there were nearly 400 aircraft wiring failures, the FAA said. Loose, chafed and broken wires account for roughly 84 percent of all wiring problems.

Damaged wiring can be a fire hazard, while engine oil, hydraulic fluids, galley spills and bathroom fluids can coat wire bundles, making them grimy and attracting dust.

Wiring prompted fresh concern after the 1996 TWA Flight 800 explosion. Investigators believe sparks triggered by a wiring failure ignited vapors in the jumbo jet's center fuel tank. The plane broke apart over the Atlantic off New York, killing all 230 passengers and crew.

Two years later, Swissair Flight 111 crashed off Nova Scotia due to a fire. While investigators never determined an exact cause, suspicion centered on an electric cable.

The disasters spawned safety initiatives, including fuel tank modifications. But post-crash analyses revealed wiring problems may not always be tied to age. They can also be linked to installation and maintenance shortcomings.

Click image for higher resolution

(Reuters)

Air Wing Toolbox: Tackling An Aging-Aircraft Wiring Risk

by John C. Milliman

Engineers working with NAVAIR's aging aircraft integrated product team (AAIPT) are teaming with industry to develop a new circuit-breaker technology to protect commercial and military aircraft from the effects of aging wiring by 2002. This technology will improve safety, reliability and readiness for all aircraft. A photo of a Navair engineer holding an arc-fault circuit breaker.

Chuck Singer, an electrical engineer in NAVAIR's electrical-power-system division, is the "point man" for a program to develop an arc-fault circuit breaker to prevent aged or damaged electrical wires from causing catastrophic problems.

"We currently use the same basic circuit protection Edison did in 1910," said Singer. "It works well and consistently for bolted faults and overloads in a tough environment, but it isn't designed for arcing faults." Thermal, or "bolted," faults occur when two wires touch each other solidly for a classic short circuit.

Recent aviation mishaps focused investigators on the problems of aging aircraft wiring, specifically hard-to-detect arcing faults. The problem, according to Singer, is that current aircraft circuit breakers, like those in residential use, are designed for bolted faults. Arc-fault circuit breakers are designed to detect and prevent electrical arcing caused by breaks in wire insulation before it can lead to a fire or other catastrophe. These faults happen where microscopic cracks, abrasions, or broken insulation occur in old wire. They also exist when wire is improperly installed or maintained.

"From July '95 to December '97, the Navy had 64 in-flight electrical fires," Singer stated. "Of those, 80 to 90 percent would have been prevented by arc-fault circuit protection."

Modern civilian and military aircraft can contain hundreds of miles of wire, much of it inaccessible once the aircraft is completely assembled. This makes repair of wire damage difficult, if it's even detected at all, according to Capt. Jim Shaw (head of the Airline Pilots' Association's [ALPA] in-flight fire project team). "With reduced thickness in the insulation of the modern wires, we made them more susceptible to damage by environmental and mechanical means," Shaw said. "So what do you do, rewire a whole aircraft? "That is, in some cases, too expensive," Shaw explained. "But if you could stop the arc from starting a fire, or taking out other wires in the bundle, then the need to replace those wires becomes moot."

"The Navy does about 1,200 power-wire removals a year, each costing about $2,000," explained Singer. "And if the damaged wire is located in a hard-to-reach place, it's even more expensive. Wiring inspections are only as good as how many places you can get in to see," said Singer. "You can look in wheel wells, flap wells, pull some panels and see some wiring, but not all of it."

The Department of the Navy awarded two contracts in December 1999, one each to the Eaton Corporation and Hendry Telephone Company (both experienced in producing industrial arc-fault circuit protection), but the process is still in the research and development phase.

"There are technical challenges to the arc-fault circuit breaker," explained Shaw. "The technology is sound, and a workable device for aircraft use is doable." A commerical breaker (about four-inches long) beside a one-ince aircraft circuit breaker.

"The hardest part will be the size," he added. "Fighters and some commercial aircraft, where space is at a premium, are going to be more difficult. Residential-arc-fault circuit breakers must be reduced in size by at least 50 percent to be used in aircraft," Singer explained.

Reducing the size on the electronic side isn't the biggest challenge; it's making the Two prototype breakers are about an inch-and-a-half wide and show the progess made toward minaturization. mechanical part of the breaker smaller. Leverage actually "pops" open the circuit once a fault has been detected by the electronic side. Miniaturizing that leverage reduces the force available to overcome the electromagnetic force generated by the current that keeps the breaker closed and the circuit complete.

Another challenge, according to Bob Ernst, head of the AAIPT, is getting the arc-fault breaker to tell the difference between a real fault in the circuit and transient-electrical signals that pose no threat. It is not a simple task to take technology developed for residential use, where the electrical signals of common devices aren't so varied or complicated, and re-engineer it for use in aircraft. This is necessary because transient electronic "signatures" are more varied and complex today. "For example," Ernst said, "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.

"This isn't simple," he continued. "That's why it isn't getting done overnight. The Navy, FAA, Air Force, ALPA, NASA, and industry are working together to develop a common specification. It's better to spend a little extra time up front to make sure we get it right.

"If the breaker is always popping for false alarms because we didn't get the programming right," said Ernst, "then maintainers out in the field are going to pull them, set them aside, and put back the old breakers. Then what will we have accomplished? You can't just throw something out there with a high false-alarm rate. We know the urgency of the issue, and we are all working as fast as we can, but we have to get it right," Ernst added.

Singer thinks flying a prototype breaker will happen soon, though. "We should be flying a prototype breaker in October 2001, in the Navy equivalent of a DC-9 and start to buy them in 2002," he stated.

Why is the military working jointly with industry and the airlines? "The problems in the civilian fleet and the military fleet are both similar and different," explained Shaw. "The civilian fleet has more cycles and hours in a shorter period of time, and the military fleet operates in a harsher environment. Their loading shock is much greater. So, each will see earlier failures of different types and, therefore, can learn from each other."

The participating agencies eagerly anticipate the new circuit breaker. "It answers a lot of serious problems we have with wiring," stated Shaw. "The Navy, in particular, Dick Healing's aircraft wiring and inert gas generator working group, has been instrumental. Without them, this may not have gotten started for years."

The effort to develop the aircraft arc-fault circuit breaker is being jointly funded by NAVAIR, the Office of Naval Research, and the Federal Aviation Administration. Additional funding is being contributed by industry.
Mech April - June 2001