NAVAL AIR STATION, Patuxent River, MD – The arc fault circuit breaker breezed by an important milestone on its way to protecting civilian and military aircraft from wire related mishaps recently when it successfully passed its last battery of ground testing here.

With ground testing complete, the technology will start actual flight testing in a 727 supplied by the Federal Aviation Administration, and a Navy C-9 (DC-9), currently scheduled to begin in August.

The arc fault circuit interruption technology is being developed jointly by the Navy, the FAA and industry to protect aging aircraft from wire-related problems.

Prototype breakers from Eaton Aerospace, one of two contractors developing AFCI technology under a joint NAVAIR, Office of Naval Research and FAA contract, were tested both at Eaton facilities and the Electrical Power Systems Lab here in four environmental tests. Eaton technicians performed two tests, for temperature/altitude and vibration, while the other two, for electromagnetic interference and electrical power, were done here, according to Chuck Singer, the NAVAIR electrical engineer leading the development effort.

The last battery of ground tests in the lab were done to determine the minimum safety of flight levels, Singer said, and built on previous testing done onboard a parked Navy C-9 and FAA 727 to ensure normal onboard aircraft functions didn’t trip the breaker.

“We wanted to be sure the actual aircraft environment (at altitude) wouldn’t trip the breaker,” explained Singer, “and that the breaker wouldn’t radiate EMI out to the other equipment.”

Although the Eaton breaker passed all its ground tests, it’s not ready to go to production.

“These tests don’t qualify the breaker for production,” Singer pointed out. “They just qualify the breaker to move on to flight testing.

“The flight tests will then validate the concept that you can fly the arc fault circuit breaker,” he added. “The individual manufacturers will then have to ‘qual test’ to commercial specifications in order to manufacture them.”

Although a government-sponsored effort, the team isn’t qualifying the breakers specifically to Navy and FAA specs, Singer explained. It, with representatives from the Air Force, FAA and industry, is working closely with the Society Of Automotive Engineering’s Protection System committee to write a commercial specification for COTS equipment with room for military requirements.

Representatives from the FAA, the Navy’s partner in the development effort, witnessed the testing as well as helped write the joint test plan effort, according the Singer.

“Successful completion of the safety of flight ground testing represents another important step toward the development of this new technology,” said Robert Pappas, manager of the FAA’s Aging Electrical Systems
Research Program. “Developing and fielding an item like AFCB is a complex process involving a multitude of activities and organizations. I’m very excited by the great progress of the effort and by the extraordinary level of interest from all corners of the aviation community."

Testing of the Eaton breaker will be followed by testing of a prototype breaker being developed by the other manufacturer under contract, Hendry Telephone Co./Texas Instruments.

“The difference between the two breakers is primarily in the detection algorithms,” Singer said.

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.

Thermal circuit breakers currently used in most military and civilian aircraft only detect classic “bolted” short circuits.
Once development is completed, the new breakers can be used in both military and civilian aircraft to lessen the risk posed by aging wiring, according to Bob Ernst, head of the Navy’s Aging Aircraft Integrated Product Team. But extensive testing must be done before the new breakers go into production.

“This isn’t simple,” Ernst said. “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.
The arc fault circuit breaker is scheduled to enter production in 2002.

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