Avionics design for testability a vendor's viewpont

Historically, testability of new avionic systems has been accorded a rather low priority by de sign engineers who were also concerned with more easily measured parameters such as sys tem performance, reliability, or ability to op erate in harsh environments. Generation of Test Requirement Documentation and calculation of the Shop Non-Ambiguity Ratio for a Unit Under Test provides a means of measuring the testability of that UUT. For digital circuit modules, this ef fort can be automated through the use of ATE with circuit simulation capability. With eight years experience in generating TRD's for several systems, GE has found that UUT's are more testable when designed by engineers who have been involved with TRD generation and validation than when they are designed by en gineers with no TRD experience. While test ability assessment and enhancement efforts usually extend development schedules and add to the cost of avionic systems while reducing their reliability, the negative impact on a development program can be minimized by utilizing a special ized team of testability/maintainability engineers to perform the testability assessment and en hancernent efforts in parallel with the system de sign engineers at the very beginning of the devel opment program before the system design is firmly documented by issuance of a drawing structure.