Embedded systems are computer systems that are part of a larger system, which generally provide real-time monitoring and control. They execute a predefined set of tasks on behalf of a real-time application, and may have special requirements based on the application domain they support. For instance, these systems are considered safety-critical embedded systems when failure may result in loss of life or high-value assets. UAVs (Unmanned Aerial Vehicles) constitute a typical application of a complex critical embedded system. One concept that can result in radically different solutions in UAVs is the use of Service-Oriented Architecture (SOA) based on standard reference model architecture. The increasing use of SOA in critical applications demands dependable and cost-effective techniques to ensure high security. In this paper we developed different kind of services for avionics with different parameters (security, reliability and performance) to provide use of SOA in a less critical part in the whole systems. Both LARISSA (Layered Architecture Model Interconnection Systems in UAV) and KBF (Knowledge Based Framework for Dynamically Changing Applications) presented in this paper can give more intelligence to UAVs and provide a new way of segregating the UAV mission from the vehicle itself. Some services were developed and a performance evaluation was conducted showing the benefits in choosing some determined services.