1.2 Required Navigation Performance 1.2.1 In order to ensure that a particular segment of airspace or route structure is safe to operate in, it is necessary to precisely define the required level of performance of aircraft systems. With regard to horizontal navigation performance, airspace is increasingly being defined in terms of a Required Navigation Performance (RNP) - a concept developed by the ICAO Review of the General Concept of Separation Panel (RGCSP), with a view to enhancing air traffic system capacity and efficiency. The RNP types specify only the navigation performance accuracy of all the user and navigation system combinations within an airspace they do not specify any other requirements of the navigation system such as, for example, reliability. The navigational accuracy requirement fora given RNP airspace is expressed as a containment value. For example, in airspace designated as RNP 10, the containment value is 10 Nautical Miles (NM) and is equivalent to the distance from the intended position (on the route centre-line) within which flights would be contained for at least 95% of their total flying time in that specific piece of airspace.
