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Old 9th Mar 2015, 18:28
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aterpster
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From the FAA AIM:

Section 2. Area Navigation (RNAV) and Required Navigation Performance (RNP)

1-2-1. Performance-Based Navigation (PBN) and Area Navigation (RNAV)

a. Introduction to PBN. As air travel has evolved, methods of navigation have improved to give operators more flexibility. Under the umbrella of area navigation, there are legacy and performance-based navigation (PBN) methods, see FIG 1-2-1. The legacy methods include operations incorporating systems approved under AC 90*45, Approval of Area Navigation Systems for Use in the U.S. National Airspace System, which allows two *dimensional area navigation (2D RNAV) within the U.S. National Airspace System (NAS). AC 90*45 describes 2D RNAV in terms of both VOR/DME dependent systems and self* contained systems such as Inertial Navigation Systems (INS). Many operators have upgraded their systems to obtain the benefits of PBN. Within PBN there are two main categories of navigation methods: area navigation (RNAV) and required navigation performance (RNP). For an aircraft to meet the requirements of RNAV, a specified RNAV accuracy must be met 95 percent of the flight time. RNP is an RNAV system that includes onboard performance monitoring and alerting capability (for example, Receiver Autonomous Integrity Monitoring (RAIM)). PBN also introduces the concept of navigation specifications (Nav Specs) which are a set of aircraft and aircrew requirements needed to support a navigation application within a defined airspace concept. For both RNP and RNAV designations, the numerical designation refers to the lateral navigation accuracy in nautical miles which is expected to be achieved at least 95 percent of the flight time by the population of aircraft operating within the airspace, route, or procedure. This information is introduced in International Civil Aviation Organization's (ICAO) Doc 9613, Performance*based Navigation (PBN) Manual (Fourth Edition, 2013) and the FAA Advisory Circular (AC) 90*105A, Approval Guidance for RNP Operations and Barometric Vertical Navigation in the U.S. National Airspace System and in Remote and Oceanic Airspace (expected publication date in late 2014) further develops this story.
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