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Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum ( )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998

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Original Message:

Posted by: T.R. Pilling ( )
Organization:HQ ACC/XR
Date posted: Sat Oct 9 22:35:27 US/Eastern 1999
Subject: Fault Isolation Requirement
We are currently writing operational requirements for a new fighter aircraft and have received a variety of feedback from contractors regarding a fault isolation requirement. The requirement is currently written as 90% automatic fault isolation to a single ambiguity group (LRU). We've been told that 90% should be easily achieved for avionics but not for hydro-mechanical systems. Is this true? If so, what do you think would be a reasonable requirement given emerging technology over the next 8-10 years? Please respond at your earliest opportunity. Thanks

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Subject: Fault Isolation Requirement
Reply Posted by: Richard Unkle ( )General Electric Transportation Systems
Date Posted: Wed Oct 13 7:58:57 US/Eastern 1999
Without knowing the specific details of a design, it can be quite difficult to specify fault detection and fault isolation requirements. However, you might try to determine what level of fault detection and isolation are needed to meet other requirements such as maintainability, availability and sparing reqirements. These are typically requirements that will drive your support costs, and the level to which you can fault isolate will surely impact that. Another alternative would be to at least develop a functional model of your system, that is representative of the LRU level. From here, expected (or hypothesized) test points can be created. Such models can then be analyzed with diagnostic analysis tools such as Detex Systems Express. The output would be the percentage of isolation to specific ambiguity group sizes that are possible, given the amount of test visibility. Trade-offs can then be evaluated as to cost of producing automated tests, adding test visibility, etc.

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