The issue of aircraft wiring safety has received widespread attention in recent years, highlighted by the unfortunate TWA 800 and Swissair 111 tragedies. As a result of these incidents and other concerns, the issue of wiring safety has been taken up by OEMs, regulatory agencies, the military, and is being addressed as part of the Aging Transport Systems Rulemaking Advisory Committee (ASTRAC).
As a result of these incidents, a number of recommendations have been made to improve aircraft wiring safety. Included among these is the development of arc fault circuit breakers for enhanced wiring system protection. SAE is taking a leadership role in this area. The AE8-B1 Protective Devices Subcommittee is developing industry specifications for arc fault circuit breakers that can provide improved aircraft wiring safety. The committee has had international representation and support from OEM's, regulatory agency personnel, the military, and component manufactures.
Arc Fault Circuit Interruption (AFCI) technology -- a relatively new technology -- has been developed to provide this supplemental protection. AFCI technology monitors the electrical circuit for arcing signals that are indicative of potentially unsafe wire conditions that could result in fires or loss of electrical circuit functionality. When coupled with an interruption mechanism, AFCI technology can be utilized to enhance aircraft wiring safety.
AFCI technology was originally developed for household applications in the 1990s, and has been proposed to improve aircraft wiring safety via retrofit on in-service aircraft and installation in new-production aircraft. Arc fault circuit breakers would replace traditional thermal circuit breakers, providing a dual-function device that augments the traditional over-current protection with electronic arc fault protection packaged in one circuit breaker device. This arc fault circuit breaker would only be slightly larger than today's devices allowing it to be retrofitted into present aircraft circuit breaker panels and installed on new production aircraft. AFCI technology can also be incorporated into solid state power controllers (SSPCs) or remote power controllers (RPCs) for applications on new aircraft that use these devices.
Although AFCI technology has been in service in many household applications in the United States for a few years, the challenges associated with adapting this technology to operate in aircraft electrical systems are significant. Complicating factors include higher and variable AC line frequencies, the need for DC protection, and lack of ground return wires required for GFI-type protection used in most household AFCI technologies. Aircraft electrical systems also present a harsh EMI environment not found in the household application.
The AE8-B1 committee is expected to complete the initial version of the specification for balloting and publication in the 3Q03. This specification will address single-phase AC performance. It will be followed by specifications for three-phase AC and 28 VDC.
The next AE8-B1 meeting, chaired by Tom Potter, Texas Instruments, will take place the week of October 20-24, 2003 in conjunction with the SAE AEISS (Aerospace Electrical Interconnect Systems Symposium) in Nashville, TN. For further information regarding the work of AE8-B1, visit the subcommittee's online Public Forum at http://forums.sae.org/access/dispatch.cgi/TEAAE8B1pf. If you have additional questions or would like information on how to participate on this subcommittee, contact Elizabeth Demoratz, SAE, at elizd@sae.org