As avionics systems become more integrated, fault isolation becomes more costly and time consuming. The development of the Collins Concept 4 avionics architecture includes a unique central avionics diagnostics function as an integral part of the avionics structure to identify failed LRUs in the aircraft for quick flight line replacement. Most troubleshooting is eliminated. Repeat squawks are greatly reduced. The central diagnostics processor uses system-wide avionics data in a flexible, table-driven processing algorithm to pinpoint LRU failures. The first application in the Beech Starship 1 is described.