No-Fault Finder

   
No-Fault Finder

 

An Ogden, Utah company called Universal Synaptics has developed a unit to help aircraft operators track down hard-to-find intermittent electrical faults.

By Ed Maher,
Special to Aviation Maintenance


The potential problems that wiring can cause are legion, and range from the worst-case of an accident to the more common mechanics response of "No Fault Found" to a discrepancy write-up.

No-fault-found findings are turning up at the extraordinarily high rate of 50 to 60 percent at commercial airlines and military repair depots. Much of this is attributable to the failure of ramp and bench tests to detect age-related problems found in avionics boxes and other aircraft components, not to mention old wiring.

No-fault-found is not simply a matter of cost and wasted manpower. There are also serious safety implications. Old, chaffed or abused wiring, corroded connectors, cold solder joints, loose grounding lugs, and other electrical components are a key cause of these mostly intermittent faults.

Being age-related, these connectivity problems are only going to get worse. Boeing estimates that more than two-thirds of the large aircraft flying today will still be flying in 20 years. In maintaining these aircraft, nothing is more frustrating for a technician than to troubleshoot for hours or even days and never find the fault that led to the pilot’s write-up.

Fortunately, there is a tool that can help track down intermittent electrical problems, especially the type that result in no-fault-found situations. The Universal Synaptics (Ogden, Utah) IFD-2000 (intermittent fault detector) applies real-world tests to aircraft components and wiring and captures data about intermittent failures at the precise nanosecond that they occur, all without having to tear apart the aircraft.

Like other testers, the IFD-2000 first tests to make certain all the wires in question are connected and their connectivity signatures are correct. Unlike other testers that repeatedly scan each individual wire in a system, over and over, in an attempt to find an intermittent connection, the IFD-2000 employs a massively parallel, super-sensitive, hardware neural network to monitor up to 256 test points (512 wire terminations) simultaneously and continuously.

Because intermittent events occur randomly in place, time, and severity, other testers on a fixed or programmed measurement cycle can miss these anomalous events. The overall boost in no fault found-detection capability when testing complex multi-wire systems with this new technology is approximately a million to one, according to Universal Synaptics.

The IFD-2000 can detect intermittent wiring faults at extremely low levels, allowing repairs to be made well before the faults cause major problems. The technician has the capability to "predict" pending electrical failures, a huge safety benefit over waiting for these failures to occur in flight.

The IFD-2000 does require some computer skill and tester familiarity to set up customized testing applications. For those that need a little help getting started, the user manual provides a step-by-step training guide which is used in conjunction with the tester verification/calibration kit, to build skill and confidence before actual testing begins.

For occasional diagnostic testing, a few generic adapter harnesses can be used to connect the IFD-2000 to a variety of aircraft or LRU circuitry. For more intense or periodic testing, more sophisticated adapter harnesses, made to fit a specific airplane type or LRU, would be necessary to make effective use of this technology. However, the cost/benefit ratio of the IFD-2000 is about 20 times greater than for a typical ATE setup when high rates of NFF (no fault found) are present, according to Universal Synaptics.

Intermittent testing can be performed in automatic or program (manual) modes. The automatic mode adjusts test stimuli and sensitivity levels as required for best performance as the test runs. In the program mode, the stimuli and sensitivity levels do not change during the test unless the operator changes them.

 

With the test wiring harness hooked up to the suspect system’s wiring, the IFD-2000 delivers the programmed stimulus to the aircraft wiring. This same stimulus is also fed directly into the IFD’s neural network for monitoring and address decoding. Should an anomalous event occur, output-latching circuitry captures the neural address of the intermittent fault event and this data is matched with the system under test nomenclature and is then displayed on a computer monitor graphically in real time. A computer-generated voice also describes the fault location via wireless headphones. This way, a technician that may be as far away as 150 feet from the IFD-2000, say in the back of the airplane creating some environmental stress, can monitor testing progress without another technician’s aid.

To be effective, the test must reflect as much as possible real-world conditions. Simulating a typical in-flight "bump" on a large aircraft can be rather difficult on the ground. Rather than having to apply large amounts of stress to create wide-open intermittents, the IFD-2000 was designed to be super-sensitive to extremely low level resistive events called micro-breaks. Often, just the vibration of walking on the floor or letting the temperature differentials stress the avionics components is enough to trigger latent anomalies.

To allow this sensitivity, the IFD-2000 is heavily protected against externally produced background noise and ground-loop problems that will cause other equipment to register false events. This protection against unwanted external noise allows testing on the ramp or shop floor that is normally only performed in EMD-protected laboratories.

 

In addition to wiring verification and intermittency reliability testing, other testing/diagnostic tools come with the IFD-2000. Wiring diagrams previously input into the computer can be accessed by the technician and any failures captured can be used to generate, on-the-fly, a complete diagram of the circuit being tested.

 

Fault history during testing is captured and can be printed for further troubleshooting and for documentation purposes to show as hard proof that, in some cases, a fault truly was not found.

Another mode, Signature Testing, uses the hardware neural network to "ping" and collect sonar-like responses from the system under test. These response patterns are used to train a sophisticated software neural network to recognize repeating circuit failures or marginal connectivity problems as airline electrical and electronics systems age.

 

In addition to these tester-related functions, this same software neural/case-based reasoner can be used to diagnose aircraft problems not associated with any IFD-2000 testing. Technicians can create their own programs to diagnose any system on the aircraft, using whatever external test equipment or observations that may be available to describe the problem.

 

Intermittent problems change, that is their nature. Connections in connectors, relays, switches, and circuit boards are under constant bombardment with vibration, moisture, contaminants, heat, and electrical surges. The manufacturer does everything it can to prevent these problems, but no manufactured product is ever perfect. Especially airplanes that are working 12 or more hours per day in widely varying and harsh conditions.

 

While the IFD-2000 was originally developed to test military avionics and has been used effectively for reliability testing in the electronics manufacturing industry, it has yet to see application by commercial airlines. It has undergone extensive laboratory tests recently by Boeing Commercial Aircraft Company. These results are still classified as proprietary but are available to airline operators and government agencies. As results from those tests become apparent, the IFD-2000 may soon see widespread commercial aircraft and space application.

 

Properly working and tested wiring is vitally important to the safety of all types of aircraft. Having the right test equipment and testing plan is the first step to preventing accidents due to age-related wiring failures.