PURPOSE AND SCOPE This Allied Publication details comprehensive guidance and recommended practice for the development of Sense and Avoid systems@ referencing and providing guidance regarding application of existing standards and best practice. It does not contain operational requirements nor equipment requirements; rather@ it is intended the bridge the gap between operational requirements and equipment requirements?? i.e.@ how to develop a system consistent with the operational requirements. A civil example of operational requirements is the ICAO RPAS Manual (Doc 10019) and of equipment requirements are Minimum Operational Performance Standards (MOPS) developed by EUROCAE and RTCA. The guidance and recommended practice herein is intended to be used by program managers and systems engineers to guide system development@ and by others involved in system development and approval as a reference. This document is intended to apply to a wide diversity of potential system architectures@ and is not intended to unnecessarily constrain implementations; therefore@ it allows varying levels of automation and operator involvement. Additionally@ it is intended to provide a common set of NATO terminology and concepts that are linked directly to operational requirements that can be used by system and standards developers. This guidance could be used in the future to develop common NATO SAA requirements approved within a STANAG. This document references the civil internationally harmonized ICAO Convention on International Civil Aviation and associated Annexes. Contracting States to ICAO may deviate from the rules within their national regulations and practices@ but the civil and military requirements pertaining to the avoidance of collision are fairly consistent across NATO Member States. According to the preamble to the Convention on International Civil Aviation@ the convention is only applicable to civil@ and not state@ aircraft. Nevertheless@ there is content@ such as due regard@ that is directly applicable to state aircraft. Additionally@ NATO Member States routinely operate military aircraft under civil rules and procedures aligning with ICAO standards and procedures during peace time. Furthermore@ States may require coordination with or approval from their civil counterparts for operational approval. Therefore@ the use of ICAO standards@ procedures@ and guidance provides a common understanding that will aid cross border operations. In this document@ civil guidance is used to provide operational context@ rather than to directly levy requirements on military state aircraft. Therefore@ although this is a NATO document@ the SAA guidance and recommended practice is likely to be useful to civil systems as well.