Abstract: Methods and apparatus are provided for determining the fault diagnosability of a health monitoring software application for a complex system. The method includes extracting data from the software application containing a relationship between one or more failure modes of the complex system and one or more evidence items of the complex system, the a priori probabilities of each failure mode occurring, and the a priori probability of each evidence item occurring. The method also includes creating one or more matrices relating the one or more FMs to the one or more evidence items. The method further includes analyzing the one or more matrices and the a priori probabilities to determine the diagnosability of each FM.