A two-component crack growth model has been developed to treat fatigue crack growth under constant and variable amplitude loading. The model is based on a concept introduced by Paris which relates the crack growth to the instantaneous plastic zone size ahead of the crack-tip. This concept was applied to describe crack growth in the presence of cyclic and primary plastic flow. The model was formulated on an incremental basis in which a particular component of the model is integrated about a discrete portion of the load excursion. The model includes the effects of cyclic and monotonic crack growths and crack closure. The results for fatigue crack growth data reported in the literature for multiple overload and severe flight sequences are compared with the model predictions. The model was shown to describe accelerated crack growth behavior typically observed during these sequences. Acceleration effects occur in the presence of primary plastic flow which is related to the ductile tearing mechanism and is not dependent upon crack closure or other load-history effects. Moreover, the model describes the phenomenological variation of the acceleration effects over such sequences. The predicted crack growth agrees well with the experimental data.