Abstract: The present invention is directed to an automated diagnostic tool having a soft structure architecture that can be easily and quickly used to troubleshoot systems and subsystems, i.e., assemblies, on aircraft such as the AH-64 helicopter. The tool includes a laptop computer loaded with a troubleshooting software program, which evaluates assembly status messages traveling on a 1553 digital communications bus that links the aircraft systems and subsystems together. The tool obtains the messages by listening on the 1553 bus. The program includes listings of the assemblies, a set of pass/fail tests for evaluating the status information, and a set of relationships that numerically correlate test outcomes with different assemblies. Based on the test results and the relationships, the tool indicates which assemblies are the most likely cause of equipment malfunctions indicated by the test outcomes.