With the functionality of most embedded systems based on software (SW), interactions amongst SW modules arise, resulting in error propagation across SW them. During SW development, it would be helpful to have a framework that clearly demonstrates the error propagation and containment capabilities of the different SW components. In this paper, we assess the impact of inter-modular error propagation. Adopting a white-box SW approach, we make the following contributions: (a) we study and characterize the error propagation process and derive a set of metrics that quantitatively represents the inter-modular SW interactions, (b) we use a real embedded target system used in an air-craft arrestment system to perform fault-injection experiments to obtain experimental values for the metrics proposed, (c) we show how the set of metrics can be used to obtain the required analytical framework for error propagation analysis. We find that the derived analytical framework establishes a very close correlation between the analytical and experimental values obtained. The intent is to use this framework to be able to systematically develop SW such that inter-modular error propagation is reduced by design.