An increasing requirement for satellites, space probes and (unmanned) aircraft is that they exhibit robust behaviour without direct human intervention. Autonomous operation is required in spite of incomplete knowledge of an uncertain environment. In particular, embedded equipment that processes sensing data must consider uncertain input parameters while managing its own activities. We show how uncertainty may be addressed in constraint-based planning and scheduling functions for aerospace equipment, contrasting with some current practice in Integrated Modular Avionic (IMA) design. We produce a conditional plan that takes account of foreseeable contingencies, so guaranteeing system behaviour in the worst case. Executing a branch of the plan corresponds to synthesising a deterministic finite state automaton capable of discrete event commanding of an avionic sub-system. Experimental results show the feasibility of the approach for realistic aerospace equipment.