Bright spark spots short circuits

A device that emits a high-voltage spark lasting for nanoseconds could help locate potentially dangerous intermittent wiring faults in aging aircraft before they become a problem. The product, called PASD (Pulsed Arrested Spark Discharge) has been patented by US government research facility Sandia National Laboratories.



Using PASD could make it financially feasible for airlines to quickly diagnose and repair the hard-to-locate intermittent faults that have plagued the industry and proven costly in lost revenue due to aircraft downtime.



Sporadic short circuits occur where two exposed conductors, or a conductor and aircraft frame, make temporary contact during flight. Vibrations caused by turbulence may cause wires to touch, interrupting power to sensitive electronics and possibly damaging wires.



These conditions are tricky to diagnose when the aircraft is stationary because the shorting wires have often shifted back to a non-shorted state. Sometimes these breaks or missing insulation can barely be seen by the naked eye. Traditional wire-test systems have great difficulty finding these faults.



PASD is about the size of a small suitcase. It 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.



Intermittent electrical short circuits in aging commercial aircraft 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 or TWA 800.



PASD works by making the short circuit manifest before it normally would and on the ground so that technicians can fix it. It sends a nanosecond pulse of electricity along aircraft wiring bundles. The tiny pulse is at such a high voltage 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 aircraft, the electrical pulse will jump from the smallest wiring insulation fault, which to ordinary instrumentation seems undamaged, either to the bulkhead or to another nearby damaged wire. The amount of time it takes for the current to return to its source is analysed by the equipment to tell within centimetres how far the break is from the test entry point.



“Rather than reacting to a problem, these systems can find a fault before it manifests into a catastrophic event,” said 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.”