By John Milliman

TEAM Public Affairs, Patuxent River

Engineers working with the Naval Air Systems Command’s Aging Aircraft Integrated Product Team here are teaming with industry to develop a new circuit breaker technology that will protect commercial and military aircraft from the effects of aging wiring by 2002.

Chuck Singer, an electrical engineer with NAVAIR’s Electrical Power System Division here, is the "point man" of a program to develop an aircraft 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 contact 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 that arcing can lead to a fire or other catastrophe. Such faults are prone to occur where microscopic cracks, abrasions or breaks in the wire’s insulation result as the wire ages, or is improperly installed or maintained.

"From July ’95 to December ’97, (the Navy) had 64 in-flight electrical fires," Singer stated. "Of those 64 wire fires, 80-90 percent would have been prevented by arc fault circuit protection." The "fires" were mostly contained and did not result in loss of an aircraft.

Since 1990, according to Singer, only one aircraft has actually been lost to a "wire fire."

Modern civilian and military aircraft can contain literally hundreds of miles of wire, much of it inaccessible once the aircraft is completely assembled and making repair of wire damage difficult, if it’s even detected at all, according to Capt. Jim Shaw, head of the Air Line Pilots’ Association’s In-flight Fire Project team. "With the reduction in the thickness of the insulation of the modern wires [to keep weight and space down] 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, prohibitively 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."

Navy and Marine Corps maintainers also recognized the problem, but couldn’t find an affordable solution.

"The Navy [has been] doing about 1,200 power wire removals a year, each at a cost of about $2,000," explained Singer. "And if the damaged wire is located in a hard-to-reach place, it’s even more expensive."

Contributing to the problem was that maintainers were only replacing the damaged wire they could find.

"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."

Even though the Department of The Navy awarded two contracts in December, 1999, one each to the Eaton Corporation and Hendry Telephone Company (both of whom are experienced in producing industrial arc fault circuit protection), 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 should be easily made a workable device for aircraft use."

"The hardest part will be the size," he added. "Circuit breaker manufacturers feel they can shrink the size enough for use in most of the commercial fleet. 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 of the electronic side isn’t the biggest challenge, either — it’s reducing the size of the mechanical part of the breaker. The mechanical part of the breaker uses leverage to actually "pop" 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 keeping the breaker closed and the circuit complete.

Another challenge, according to Bob Ernst, head of the Navy’s Aging Aircraft team, 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. No simple task when it comes to taking technology originally developed for residential use where the electrical signals of common devices aren’t so varied or complicated and re-engineering (and qualifying) it for use in aircraft where transient electronic "signatures" are more varied and complex.

"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."

The agencies jointly developing the specification agree that if the arc fault circuit breaker has too many false alarms, it won’t be used.

"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 the old breakers back in. 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 projects flying a prototype breaker soon, though.

"We should be flying a prototype breaker in October 2001 in a Navy C-9 (Navy equivalent of a DC-9) and transition to procurement beginning in 2002," he stated.

Why is the military working jointly with industry and the airlines?

"The aging problems in the civilian fleet [and] the military fleet are both similar and different," explained ALPA’s Shaw. "The civilian fleet has more cycles and hours in a shorter period of time and the military fleet operates in (usually) a harsher environment. And loading shock is much greater. So each will see earlier failures of a certain type than the other and can therefore learn from the other’s aging history."

Despite the challenges, 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 (director of the Secretary of the Navy’s Office of Safety and Survivability) 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.