A Diagnostics, Prognostics and Health Management (DPHM) solution is proposed for the operation of the aircraft environmental control system (ECS) cross flow heat exchanger. In particular, a dynamic model is derived and applied to on-line detection of fouling in the aircraft ECS cross flow plate-and-fin heat exchanger. Predictive maintenance actions can be scheduled as per the on-line detected fouling status of the specific component, supporting condition based maintenance. The heat exchanger model is of the lumped state space form, where the state consists of the core and fin temperatures. The ratios of the thermal capacities of the masses of the two air streams to the thermal capacity of the core itself are neglected, and the model parameters' functional dependency on mass flow rate and influence of secondary surfaces (fins) are taken into account in order to accurately describe the dynamic behavior of the heat exchanger. Since the parameters are functions of mass flow rate, as are the core and fin temperatures, and the model is nonlinear in the state variables, an extended Kalman filtering (EKF) algorithm is applied to estimate the state dependent parameters. The effectiveness of the model's formulation is supported by the quality of the corresponding predicted results, which in turn are validated via experimental tests.