This work presents a proposal to use aspect orientation in the analysis and design of Distributed Embedded Real-time Systems (DERTS). These systems have several requirements directly related to their main characteristics, the so-called Non-Functional Requirements (NFR), which refer to orthogonal properties, conditions, and restrictions that are spread out over the entire system. Pure object-oriented methods do not address successfully those so called cross-cutting concerns, so new technologies, like aspect orientation, are applied in order to fulfill this gap. The paper presents DERAF - Distributed Embedded Real-time Aspects Framework, an extensible and high-level framework (i.e. implementation-independent) to handle NFR of DERTS at earlier design stages. DERAF combines the use of aspects with RT-UML, aiming to separate the handling of non-functional from functional requirements in the Model Driven Design of DERTS. The paper presents the use of DERAF on a case study of an unmanned air vehicle (UAV).