We describe an approach for modeling and diagnosing complex multi-modal sys
tems. A novel feature of this approach is the proposed method for integrati
ng multiple specification modalities. We apply this approach to a real-worl
d rocket engine turbopump. The example model consists of two submodels, one
describing liquid flows, and one describing mechanical vibrations. Typical
methods for modeling such systems will treat these two modalities as being
completely disjoint, even though they have significant interactions. We de
scribe a method for integrating these sub-models using variables that play
different roles in the different sub-models. We focus on how the integrated
causal network model allows us to diagnose a more complete and physically
plausible set of faults than by using the independent sub-models.