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...

Defining the challenge

“This is a science problem, a test coverage problem, a probability problem,” he says. In order “to catch intermittent faults on the ground, you must have phenomenal testing speed (sensitivity) and 100 percent bandwidth.” Anderson’s position is that if we want to reduce NFF and CND repeats we have to change our mindset, methods, and technology. “We can employ the most skilled technicians and engineers with the most comprehensive maintenance data collection systems and likely reduce NFF to some degree.”

To significantly improve AMTs’ score cards, we must be able to detect and identify intermittent faults as they manifest in real time. “The proper technology for the task must be able to test all of the failing system’s lines, all of the time, in a simultaneous and continuous fashion,” Anderson says. Universal Synaptics Corp. has a product that can.

Intermittent fault detection system

The intermittent fault detection and isolation system (IFDIS) is state-of-the-art testing technology that is specifically designed to detect, isolate, and identify the root cause of an intermittent fault. When you place an LRU in the IFDIS it first “interrogates and stores the as-designed wiring configuration from a good unit and then based on that “gold” configuration, will detect any open, short, ohmic, impedance, drift, or miswiring problems in subsequent units under test (UUT).”

The IFDIS simulates the operating environment and can subject an LRU to -100 F to 350 F. Additionally, it has a 2,205-pound-foot vibration platform with a 2-inch peak-to-peak displacement and 78-inch/second velocity that can induce a range of vibrations. Once environmental testing begins, it continuously and simultaneously monitors every single electrical path in the chassis.

“The IFD, intermittent fault detector, finds and isolates intermittent events, as short as 50 nanoseconds.” Once detected, the fault and its location is automatically documented and displayed to the technician via high resolution fault isolation graphics which show the exact circuit path and connection points that are intermittent. The IFDIS process allows the technician to surgically repair the root cause of the intermittent fault.

A technical solution

Working with prime contractor total quality systems (TQS) and the U.S. Air Force, Universal Synaptics has been able to return to service more than $26 million worth of flight hardware previously considered “unrepairable,” more than double the mean time between depot repairs (an additional savings of $1.3 million annually), while reducing maintenance squadron re-work by 50 percent. This was achieved by the IFDIS’s ability to quickly and correctly detect and isolate intermittent faults. Air Force technicians understood that repairing an intermittent circuit was not difficult; it was detecting and isolating the intermittency that presented the challenge. With IFDIS, that diagnostic challenge is gone.

I had an opportunity to discuss the IFDIS in greater detail with Sami Mansour, director of the 523rd Avionics Maintenance Squadron at Hill Air Force Base in Layton, UT. According to Mansour, there are two IFDIS at Hill; one is being used by the 523rd Electronics Maintenance Squadron and the other by the Software Engineering Lab. He says that the IFDISs are easy to use and dependable.

With the IFDIS, it takes technicians about two hours to test a typical avionics LRU and test results as extremely reliable. Once the IFDIS identifies and isolates an intermittent circuit, open or short, the technician knows exactly what the problem is and where to go to fix it. It appears that the IFDIS and numbers are working for the 523rd. Mansour estimates that they have achieved more than a “12 times return on investment and that continues to grow.”

Accurate detection

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