The FAA planned Data Communications Network Service (DCNS) will enable digital air/ground (A/G) communication between Air Traffic Control (ATC) facilities and VHF Digital Link (VDL) Mode 2 (VDL-2) equipped aircraft. In successive program segments, ATC services will evolve to include both 'essential' and 'safety critical' applications. Appropriate requirements will be imposed on the DCNS to transport these applications. These requirements will place challenging demands on the performance of the VDL-2 A/G links.Predicting and accommodating the impairments to the air-ground radio channel are necessary for the DCNS provider to deploy a design that assures endto-end performance requirements are satisfied. Good engineering practice requires the characterization of the air-ground radio channel and development of detailed link budgets. Certain significant VDL-2 channel impairments are intermittent (temporal) and add complexity to the analysis.