This document provides the Operational Services and Environment Definition (OSED) for the Detect and Avoid (DAA) capabilities to support very low level (VLL) operations conducted by unmanned aircraft systems (UAS). It provides a basis for assessing and establishing operational, safety, performance, and interoperability requirements for the DAA capabilities. It seeks to characterize attributes of UAS and to define their relationship to external supporting services, other airspace users, and the environment in which unmanned aircraft (UA) are operated. This OSED captures high level operational requirements that are derived as being necessary for the candidate’s capabilities. It is intended to be used as a supporting document for implementation of ED-78A / DO-264 process in the definition of Safety and Performances Requirements (SPR) and Interoperability requirements (INTEROP). It is considered as a baseline to support the development of Minimum Aviation System Performance Standards (MASPS) and Minimum Operational Performance Specification (MOPS).