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Sandia Technology logo A quarterly research and development magazine.

Fall 2006
Volume 8, No. 3

SANDIA TECHNOLOGY

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Finding airplane short circuits before they cause trouble

The challenge to aeronautical engineers has been how to locate an intermittent wiring fault before — not after — it becomes a problem and scuttles an aircraft. Intermittent electrical short circuits in aging commercial airliners range from the trivial to the deadly. They can make cabin lights blink, air conditioning falter, or even cause fatal crashes, as with flights SwissAir 111 and TWA 800.

Boeing 737 Larry Schneider (left) and Mike Dinallo prepare to employ the PASD diagnostic on a wiring bundle in the cockpit of a retired Boeing 737. (Photo by Randy Montoya)
The trick of the Sandia-patented Pulsed Arrested Spark Discharge, or PASD, is to make the short circuit appear before it normally would and to do so on the ground so that technicians can fix it. To achieve this, the Sandia method sends a nanosecond pulse of electricity, fiercely propelled by high voltage, along airplane wiring bundles. The tiny pulse is powerfully driven so that it can jump gaps in slightly frayed insulation but has so little energy that it is harmless.

Because the voltage is higher than that normally used in airplanes, the electrical pulse will jump like a rabbit from the smallest wiring insulation fault (which to ordinary instrumentation seems undamaged) either to the bulkhead or to another nearby damaged wire. That spark — like static electricity leaping from hand to doorknob — in effect lights up the invisibly damaged spot like a tracer bullet lights up a night target. The amount of time it takes for the current to return to its source is analyzed by the automated test-set to tell within inches how far the break is from the test entry point.

The device, about the size of a small suitcase, can be plugged into aircraft-installed wire harnesses, 40 wires at a time, to check for the very small insulation breaks associated with intermittent faults.

“Rather than reacting to a problem, these systems can find a fault before it manifests into a catastrophic event,” says Sandia team leader Larry Schneider. “Rather than ripping apart the fuselage for access to a faulty harness that may run the length of the plane, airline mechanics will be able to use this new tool to efficiently locate and repair the intermittent fault.”