This paper describes a process group membership protocol for distributed real-time systems, that use a communication network which supports both timetriggered (TT) and event-triggered (ET) communication. The protocol allows a group of cooperating real-time processes to establish a consistent view of each other's operational status, i.e. working correctly or not. The aim is to provide an application independent membership service in systems where several distributed real-time tasks share processing nodes. We assume that each such task consists of several processes executing on different nodes and that each node can execute processes belonging to different tasks. The protocol is applicable to any application domain, but has been developed for automotive active safety systems. Here, typical distributed real-time tasks include anti-lock braking, stability control and collision mitigation. In such systems, a membership service provides invaluable support for implementing fault-tolerance and graceful degradation.