Intermittent faults are a growing problem and many of the maintenance issues of which repair facilities contend with are directly related to interconnectivity problems on the aircraft Electrical Wiring Interconnect System (EWIS) or within Line Replaceable Unit/ Weapon Replaceable Assembly (LRU/WRA) electronic equipment. Hard failures, where wiring issues are evident, are relatively routine to detect and repair, and not all hard failures involve wiring. However, major electrical issues and even critical down-line failures may occur when an electrical fault appears only intermittently, in short duration, under operational conditions (such as high G-force loading and extremes in temperature or stress, or vibrational states) that are difficult to replicate. These intermittent faults are difficult to identify, isolate, and ultimately repair.
There was no standardized, automated, DOD-approved process to consistently detect these faults. Industry developed Intermittent Fault Detection (IFD) and diagnostic equipment to identify these faults. In addition, this industry development included the integration of the diagnostic equipment with environmental test chambers and vibration tables to simulate the LRU/WRA or EWIS operating environment.
The challenge is environmentally stimulating LRU/WRA or EWIS in the aircraft. Care must be taken to environmentally stimulate LRU/WRA or EWIS, but not damage the aircraft components. In addition, access and space on the aircraft is limited, so that any environmental stimulation must be small and compact. Further consideration must also be given in regard to the Electromagnetic Interference (EMI) and aviation fuel environment of an aircraft.
Intermittent faults include short duration opens and shorts, degraded and intermittent signals, and insulation degradation. The magnitude of the challenge is daunting, with the DOD spending approximately $2B annually just removing and replacing LRUs/WRAs and EWIS that, when tested, are determined to be No Fault Found (NFF). Additionally, legacy electronic components are experiencing increasingly reduced reliability because of component age, usage, and in some cases maintenance actions. Intermittent faults are mechanical in nature and can include failures in solder joints, wiring, wire wraps, connectors, etc., which only manifest as operational failures due to temperature, vibration, and other external environmental stimuli. The duration of these intermittent events can range from nanoseconds to seconds, may oscillate repeatedly during an event or may just be a single occurrence during a given testing session. Intermediate and depot maintenance actions, such as the reseating of a degraded connection, solder joint, etc., can temporarily cause the intermittent connection to function properly for days, or even weeks after, and may only manifest as a repeat operational failure after several months. This leads to a constant revolving cycle (removal, maintenance testing resulting in NFF, and subsequent reinstall on aircraft) of removal/re-installation of EWIS and LRU/WRA on the aircraft.
Guiding information is available in the following references:
- MIL-PRF-32516, Electronic Test Equipment, Intermittent Fault Detection, and Isolation for Chassis and Backplane Conductive Paths.
This reference provides performance requirements for Intermittent Fault Diagnostic Equipment. Appendices A through C provide guidance in regard to developing vibration, temperature, and combined vibration/temperature environment stimulation profiles.
- MIL-STD-810, Environmental Engineering Considerations and Laboratory Tests.
The guidance and test methods of this standard are intended to: (1) Provide guidance of the development of materiel life cycles and aid in the development of environmental stress sequences, durations, and test levels; (2) Be used to develop analysis and test criteria tailored to the materiel and its environmental life cycle; (3) Evaluate materiel performance when exposed to a life cycle of environmental stresses; (4) Identify deficiencies, shortcomings, and defects in materiel design, materials, manufacturing processes, packaging techniques, and maintenance methods; (5) Demonstrate compliance with contractual requirements.
The following are some very simple solutions that have been discussed for providing aircraft environmental stimulation:
- Hairdryer: Can provide high-temperature stimulation. This is a very simple solution but has limited temperature control, only high temperature, electric motor brushes (issue around aircraft fuel), etc.
- Palm sander (without sander paper): Can provide vibration stimulation. This again is a very simple solution but has limited vibration control, electric motor brushes (issue around aircraft fuel), etc.
Neither of these solutions provides cold temperature stimulation.
Aircraft LRU/WRA* or EWIS environment stimulation device, which has the following capabilities:
- Small compact design.
- Low cost.
- Capable of providing cold, hot, and/or vibration environment simulation. These capabilities shall be controllable and output levels shall be displayed.
- Capable of working in military aircraft EMI and fuel environments.
- Powered by 120-volt, 60 Hz, or internal battery. May be powered by hangar or facility plug-in power, external power cart or Flight Line Electrical Distribution System (FLEDS) 115-volt, 400 Hz, or 28 VDC. Not required to work on all three AC and DC electrical inputs.
* Note that LRU/WRA components may not be able to be environmentally stimulated on the aircraft. Intermittent Fault and Isolation testing of LRU/WRA components is concerned with chassis and backplane circuits and their wiring harnesses and internal wiring harnesses which will require the removal of internal printed circuit boards to test.
Briefings and white papers addressing any of the aforementioned technologies should be proposed. Responses will be selected for full development and used, at a minimum, to inform requirements for Aircraft Intermittent Fault Operational Environment Stimulation. Unique technologies that demonstrate technical maturity may be recommended for future collaborative R&D projects.
This effort is potentially the first phase of a three-phased look at Aircraft Intermittent Fault Operational Environment Stimulation. The first phase is focused on stimulation equipment used on the ground and interfaced with the aircraft. Phase two will be focused on stimulation equipment that can be used off-board the aircraft and brought on board during flight. Phase three will be focused on stimulation equipment that can be installed in the aircraft.
Interested parties should complete the following:
- Background of capability summary (please include how your proposed technology could be transferred from commercial to a military application).
- Examples of where the capability is currently used if any.
- URLs to corporate presentations including engineering, manufacturing, and testing capabilities.
- Cost Summary Form
Interested parties should complete the following form no later than Tuesday, September 29. Any questions can be directed to Dana Ellis at email@example.com.