As today's military and commercial aircraft age past their teen years, the many kilometers of wiring buried deep within their structures begin to crack and fray. Once thought to be rare and benign, such faults are found by the hundreds in a typical aircraft. Unlike obvious cracks in a wing or an engine, though, damaged wire is extremely difficult to detect. But the resulting arcing and electromagnetic emissions can be just as deadly: faulty wiring has been blamed for the downing of Swissair 111 near Nova Scotia in 1998 and of TWA 800 off New York's Long Island in 1996 [see Photo]. Indeed, any densely wired system is vulnerable--the space shuttle, nuclear power plants, subways and railroads, even the family car.
Public scrutiny has prompted strongly worded recommendations from the likes of NASA, the U.S. Federal Aviation Administration, and the National Transportation Safety Board (NTSB) [see "Government and Industry Take Action"]. "The safety of the nation's wire systems is an issue of major importance to us all," noted a White House report issued last fall. Several months earlier, the NTSB concluded its lengthy investigation of TWA 800 with the verdict that a short circuit sparked an explosion in the center wing fuel tank. The condition of the wiring, it noted, was "not atypical for an airplane of its age." Among the NTSB's recommendations was to incorporate into aircraft "new technology, such as arc-fault circuit breakers and automated wire test equipment."
Solutions are not straightforward. Among the most promising technologies are advanced reflectometry methods, for routine maintenance; so-called smart wire systems, for continual, on-the-spot wire testing; and arc-fault circuit breakers and advanced fire suppression techniques, for minimizing damage and injury should a fault occur. Remaining challenges include detecting the minuscule insulation breaks that encourage arcing; optimizing the benefits and mitigating the risks of the various wire testing techniques; and getting a better handle on the labyrinthine complexity of aircraft wiring systems.
