Obsolescence replacement and testing — reducing cost through commonality

The aviation industry has many aircraft in use after more than twenty years of life with some aircraft achieving the fifty years of life milestone. The avionics aboard the older aircraft are based on circuitry elements with diminishing or no manufacturing sources. Entire families of integrated circuits are no longer available, such as the early Intel processors and peripherals, 54C series CMOS logic and LH0075/LH0076 voltage references. Obsolescence replacement programs must preserve the investment in formal FAA certification for affordability, which makes work-alike solutions technically attractive. The voltage reference replacement is fairly straightforward using a newer series reference. The logic replacement is less straightforward because even though the logic diagram may be a duplicate, modern logic operates at reduced voltage levels. Processors and programmable peripherals present additional challenges, as the code running on the processors represents a large secondary investment multiplying the cost of replacement. The documentation for older systems may be poor quality, including illegible drawings, missing data and incompatible data formats. The high cost of overcoming these obstacles to redesign led to a search for cost reductions in other areas. Re-use of an automated test station (ATS) and development of test program set (TPS) assets proved to be a cost reduction opportunity in the manufacturing, integration, acceptance and maintenance of the replacement avionics. Past practice has been to design a unique separate test solution at each level of test, incurring significant non-recurring cost. Selecting an existing maintenance level ATS for all levels of test avoids the significant non-recurring costs of specialized ATS at each level. Developing electronic box and circuit card TPSs compatible across all test phases reduces cost over the life of the redesigned avionics. The paper is a case study of a recent avionics obsolescence replacement program, which included the test solution used. An existing ATS, single electronic box level TPS and single circuit card TPS per circuit card type were used for all phases of test. Integrating the legacy avionics on the TPSs ensured functional equivalence would be achieved with the new avionic assets. The unique fault universe for each level of test will be covered, like fabrication defects for manufacturing, design defects for integration, fabrication & infant mortality defects for acceptance, and component failures for maintenance.