INSTRUMENT PROCEDURES HANDBOOK
 

REQUIRED NAVIGATION PERFORMANCE

As RNAV systems grow in sophistication, high technology FMS and GPS avionics are gaining popularity as NDBs, VORs, and LORAN are being phased out. As a result, new procedures are being introduced, including RNP, RVSM, and minimum navigation performance specifications (MNPS). ICAO defines an RNP X specification as requiring on-board performance monitoring and alerting. Even such terms as gross navigation errors (GNEs) are being introduced into the navigation equation. If you commit a GNE in the North Atlantic oceanic region of more than 25 NM laterally or 300 feet vertically, it has a detrimental effect on the overall targeted level of safety of the ATC airspace system in this region. This applies to commercial operators, as well as Part 91 operators, all of whom must be knowledgeable on procedures for operations in North Atlantic airspace, contained in the North Atlantic MNPS Operations Manual.
RNP types are identified by a single accuracy value. For example, RNP 1 refers to a required navigation performance accuracy within 1 NM of the desired flight path at least 95 percent of the flying time. Countries around the world are establishing required navigation performance values. For Federal Airways in the U.S. that extend 4 NM from either side of the airway centerline, the airway has an equivalent RNP of 2. Figure 3-42 on page 3-38 shows ICAO RNP containment parameters, including reference to lateral and longitudinal total system errors (TSEs).

RNP requires you to learn new procedures, communications, and limitations; and to learn new terminology that defines and describes navigation concepts. One of these terms is RNP Airspace, a generic term designating airspace, routes, legs, operations, or procedures where minimum RNP has been established. P-RNAV represents a 95 percent containment value of 1 NM. B-RNAV provides a 95 percent containment value of 5 NM. RNP is a function of RNAV equipment that calculates, displays, and provides lateral guidance to a profile or path. Estimated position error (EPE) is a measure of your current estimated navigational performance, also referred to as actual navigation performance (ANP).

RNP RNAV is an industry-expanded specification beyond ICAO-defined RNP. Some of the benefits of RNP RNAV includes being an aid in both separation and collision risk assessment. RNP RNAV can further reduce route separation. Figure 3-43 depicts route separation, that can now be reduced to four times the RNP value, which further increases route capacity within the same airspace. The containment limit quantifies the navigation performance where the probability of an unannunciated deviation greater than 2 x RNP is less than 1 x 10-5. This means that the pilot will be alerted when the TSE can be greater than the containment limit. Figure 3-44 shows the U.S. RNP RNAV levels by airspace control regions, including RNP 2 for the en route phase of flight, and Figure 3-45 on page 3-40 illustrates the U.S. standard RNP (95%) levels.

 
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