DoD Maintenance Symposium
There is a growing problem that threatens the airworthiness, mission readiness and safety of aircraft. However, recent technical developments have made possible a new inspection method that greatly mitigates this threat, and now multiple case studies are validating the effectiveness of this new capability.
The growing problem is intermittent faults in new and aging aircraft electronic boxes. The recent development is the Intermittent Fault Detection and Isolation System (IFDIS), and the case studies that are validating the IFDIS thus far involve two F-16 AN/APG-68 radar system electronic boxes. Maintenance personnel well know the challenge they face when the pilot reports that a system malfunctioned during flight, but the subsequent ground test of that system shows “No Fault Found” (NFF).
It is apparent that there is an intermittent problem somewhere in the system, but the frustrated maintenance crew simply lacks the equipment needed to enable them to detect and isolate the problem. Repairing the intermittent circuit is seldom difficult; the difficult task is detecting and isolating which circuit within the box is intermittent.
An intermittent fault, or momentary “open,” can be due to a number of different conditions including a cracked solder joint, a corroded contact, a sprung connector receptacle, a loose crimp connection, a hairline crack in a printed circuit trace, a loose wire wrap, a broken wire, or various other conditions.
As the electronic boxes are pulled from the errant system for bench test, they often all test NFF. No repair is performed, because no problem can be detected. Conventional test equipment is simply not designed to detect intermittent circuits. Rather, conventional equipment is designed to test the electronic box for nominal operation, and it usually “averages out,” and hence hides, any short term anomalous events.
The IFDIS is a tester that was specifically designed to detect and isolate intermittent circuits in aircraft electronic box chassis. Hence, the IFDIS very effectively compliments conventional testers. The conventional testers test for nominal equipment operation, while the IFDIS detects and isolates intermittent circuits. Because intermittent faults often only occur during the vibration and/or temperature extremes experienced in an operational environment, the IFDIS includes an environmental chamber and vibration platform that subjects the box to simulated operational conditions, substantially enhancing the speed an intermittent circuit will manifest itself.
At the heart of the IFDIS is state of the art intermittent fault detection circuitry which continuously and simultaneously monitors every single electrical path in the chassis under test, while the box is exposed to the simulated operational environment. The intermittent fault detection analog neural network circuitry will detect when an intermittent event, even as short as 50 nanoseconds (0.00000005 seconds), occurs in any chassis circuit, and it identifies exactly which circuit the intermittent event occurred.
Over 195 radar radio frequency boxes and dozens of interconnecting antenna unit ribbon cables have been tested to date with unprecedented results, current day over $36 million dollars worth of flight hardware has been returned to service. Previously undetectable problems are being rapidly identified and repair shop troubleshooting time is being substantially reduced. More importantly, the IFDIS is significantly enhancing aircraft reliability, aircraft availability, mission readiness, safety and simultaneously reducing total ownership cost.