Enhancement of the Omega System Availability Model are presented which: (1) widen the range of application of the model, (2) increase the efficiency of the model algorithm, and (3) broaden the model to include more realistic characterization of the signal coverage parameters. The system availability model/algorithm is modified to apply at the geographic area unit (cell) and multi-cell level. Further modifications include: a precomputation method to speed calculation and extension of the coverage database (interpolation) from four-months to twelve months. The system availability model is extended to include the effects of random signal and noise variations. The augmented model structure in consistent with probabilistic definition of the Omega System Availability Index (PSA). (Author).