In future dynamic spectrum access (DSA) wireless networks,secondary users can make use of spectrum opportunitiesdynamically for communications. These opportunitiesare available when primary users do not use theirlicensed spectrum slots. In this paper we study the scenario where spectrum opportunities are characterized bythe ON/OFF distribution. As a result, the queueing systemcan be analyzed using the well-established theory of fluidflow models and effective bandwidth. Based on a refinementto the original effective bandwidth approximation, wederive the packet loss probability for secondary users access to the available channels. Theoretical and numericalanalyses are used to investigate the impacts of various parameters of the underlying DSA link model on the systemperformance.