We address the problem of how to adapt the quality of service of distributed, fault-tolerant, real-time applications with respect to the current failure rate that the system experiences. Our approach to that problem uses fail-awareness which is a design concept that allows clients to detect when a distributed service cannot provide certain properties due to a too high failure rate. In this paper we describe several problems that have to be solved in applications that can adapt their quality of service and show how fail-awareness can be used in such applications.