Unmanned Aircraft Systems (UAS) are increasing their communication subsystems complexity as they are using several data links both for redundancy and for tacking with different communication requirements: different ranges, bandwidth, power consumption or cost. Inside the airframe a similar tendency with respect to communications is appearing. Modern digital avionics are mainly implemented as distributed computing architectures. This work describes Marea, a middleware specifically designed to fulfill UAS communications and their application to the design of complex distributed UAS avionics.