Fixed Mobile Convergence is significantly changing the role of access networks: the same infrastructure will be serving fixed broadband access, mobile macro- and small cells. It brings new challenges on the architectural level, network availability being one of the key aspects. However, the strong cost pressure in the access networks makes extensive deployment of redundancy economically infeasible. The key for affordable availability improvement is the (application specific) identification of the most critical failures. In this paper we review the main application fields of FMC networks, differentiated by its clients (residential fixed customers, mobile macro- and small cells). The most critical failures are identified for each application, and metrics are presented for evaluating failure criticality and network availability. Finally, appropriate strategies will be proposed for improving the network availability under tight cost restrictions, and the cost and availability implications will be discussed. Availability improvement not necessarily requires protection resources; diversification network planning techniques also play an important role.