An airplane’s nervous system is its electrical wiring, and on many older aircraft, nerves are a bit raw. The polymer sheaths covering wires are subjected to “everything from deicing salts to Coca-Cola, airborne particles, vibration and rubbing against sharp corners,” says Northwestern University materials scientist Thomas Mason. Cracks, holes and thin spots in the sheaths can cause breakdowns or disaster: Investigators suspect a faulty fuel-gauge wire caused the 1996 explosion of TWA Flight 800.
Wires are for the most part inspected visually, but that’s difficult when they run through inaccessible parts of the plane. And pulling brittle wires out to look at them can actually damage them more. But Mason and other researchers in a three-year project at Northwestern aim to engineer a noninvasive wiring test by using a technique called impedance/dielectric spectroscopy, which measures the response of a wire to a range of frequencies of alternating current. Comparing the impedance response, or “signature,” of an older wire to that of a fresh, new wire could reveal the kind of damage-abrasion, holes or chemical assault-to the wire’s polymer sheathing, as well as the degree of degradation and perhaps even its location along the wire. That’s the hope, anyway. L. Catherine Brinson, leader of the Federal Aviation Administration-funded project, estimates a working prototype is at least five years off.