Finding Intermittent Faults in Aging Aircraft Systems

Most aviation maintenance technicians would probably agree that intermittent faults are our nemesis and that finding and clearing those faults in aging aircraft is extremely problematic. The resources involved in endless troubleshooting and line...


Most aviation maintenance technicians would probably agree that intermittent faults are our nemesis and that finding and clearing those faults in aging aircraft is extremely problematic. The resources involved in endless troubleshooting and line replaceable unit (LRU) swapping has a huge impact on manpower allocation and budgets. We aren’t doing so well if we use first time fixes, no fault found (NFF), cannot duplicate (CND) logbook entries, and LRU replacements as the measure of our effectiveness. There also may be a good argument that we are part of the problem.

Troubleshooting our processes

The problem would not be individual AMTs but the maintenance culture with its troubleshooting models, methods, and technology. It appears that this is not new news and there are others in our industry that hold similar views. In a June 1997 article in Avionics magazine, Walter Shawlee II, president and founder of Northern Airborne Technologies Ltd. of Canada, presents an excellent assessment of our testing practices and their limitations. He suggests that “the nature and design of the test predetermines the result. Test strategies have traditionally tended to be serial and linear with isolated steps that progress over time and terminate in a go/no-go decision.

“However, it makes the highly erroneous supposition that faults exist as discreet situations of constant duration and merely presenting the right test conditions will make the fault unambiguously known. The origin of this strategy is one of convenience, but it entrenches complex faults and intermittent problems in the test system itself making them impossible to discover or correct in the field.” Shawlee also suggests that diagnostic systems may amplify the problem. He states that “the trend to eliminate any step during testing that requires human intervention may have initial economic or conceptual appeal, but may simply set the stage for downstream problems that will remain difficult or impossible to eradicate in the field.”

Universal Synaptics Corp.

There are experts in this field. One company that specializes in troubleshooting intermittent faults in aging aircraft is Universal Synaptics Corp. Located in Utah, it has spent years in the field and lab researching and solving complex diagnostic and testing problems. Last fall it was recognized for its efforts by the Department of Defense (DoD). In November 2010, its Intermittent Fault Detection & Isolation System (IFDIS) was selected as the Great Ideas Competition winner at the 2010 DoD Maintenance Symposium and Exhibition. In February 2011, the IFDIS was selected as a Tibbetts Award winner. The Tibbetts Award is given by the U.S. Small Business Administration to honor outstanding small businesses that participate in the SBA Small Business Innovation Research program.

Ken Anderson, vice president of sales and business development, is one of Universal Synaptics experts on intermittent faults and their various causes. I asked him why we have such a high rate of NFF and CND test results for these intermittent faults, especially on aging aircraft. He explains that “as integrated circuits (ICs) and other electronic discrete parts become increasingly capable and reliable, an ever growing portion of the electronic equipment maintenance problems encountered are not component failure. They are intermittent interconnectivity problems between the electronic piece parts, like connectors, solder joints, wiring, wire-wraps, printed circuit traces and vias, flex circuits, crimps, splices, and relays.

“Depending on what report you read 40 to 60 percent of all pilot-reported aircraft system malfunctions which occur in the air are troubleshooting challenges for the AMT during follow-on ground testing. In a typical avionics system, there are thousands of internal and external circuit conduction paths moving electrons through thousands more physical interconnection points which are all aging to some degree and will fail intermittently long before they fail permanently. It only takes one of these interconnection points reaching this condition to render the LRU or wiring system unreliable.” I asked Anderson if there is a solution to this problem. He suggests that first we need to clearly understand the problem.

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