Performance-Based Navigation Best Practice Guide for ANSPs
RNP specification is navigation specification based on area navigation that includes the requirement for on-board performance monitoring and alerting; aircraft equipage; and pilot training and qualifications. RNP navigation specification values also refer to 95 percent accuracy values designated by an RNP prefix (e.g. RNP 0.3). These procedures can include vertical system accuracy as well. Another key advantage of RNP is that fixed radius paths (FRP) can be flown. FRPs can take two forms: The constant radius to a fix (RF) leg is one of the leg types that should be used when there is a requirement for a specific curved path radius in a terminal or approach procedure. The RF leg is defined by radius, arc length and fix. RNP systems supporting this leg type provide the same ability to conform to the track-keeping accuracy during the turn as in straight line segments.
Radius to Fix Leg Type3 The fixed radius transition (FRT) is intended to be used in en-route procedures. These turns have two possible radii, 22.5 NM for high altitude routes (above flight level (FL)195) and 15 NM for low altitude routes. Using such path elements in a RNAV route enables improvement in airspace usage through closely spaced parallel routes. Under PBN, operational requirements are defined as those that drive the airspace concept. These requirements may be as simple as the establishment of a new runway or as complex as 3
the introduction of a communications, navigation and surveillance / air traffic management (CNS/ ATM) infrastructure. Civil aviation authorities then evaluate options that lead to the selection of a navigation specification. A chosen navigation specification may be based on airspace configuration, traffic density, equipage and types of users, etc. Technology can evolve over time without requiring the operation itself to be revisited as long as the requisite performance is provided by the RNAV or RNP system. A thorough explanation of the process can be found in ICAO Doc 9992, PBN Airspace Design Manual. PBN procedures are commonly built to be flown by aircraft equipped with Global Navigation Satellite System (GNSS) only or can use groundbased distance measuring equipment and/or inertial reference system (DME/DME/IRS) and are in most cases developed to be flown by either type of equipage. PBN procedures may allow for closely spaced tracks and routes allowing easier airspace design standards since the route always remains the same width and is not dependent upon electronic signals from ground-based NAVAIDs with wavering signals. This applies to DME/ DME/IRS flight as well as GPS (global positioning system) flight. DME/DME/IRS flight would apply to legacy aircraft that have not been retrofitted to allow for GNSS operations and must use groundbased DME stations. Aircraft and crews capable of GNSS flight can utilise RNP and RNAV procedures allowing for a mixed environment with DME/ DME/IRS to better utilise the tightly spaced routes and various airspace configurations which can be developed to enhance ATC functions. Use of PBN procedures can reduce environmental constraints over conventional procedures by reducing greenhouse gases (GHGs) through increased efficiencies in the lateral and vertical paths, as well as improving the opportunity to constrain flight paths over less noise sensitive
ICAO Doc 8168 Vol II Part 3, Section 2, Chapter 5, para 5.2. Reproduced with the permission of ICAO.