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RNAV

Traditional IFR navigation consisted of flying from one radio beacon (NDB's at first, later VOR's)

to another - your flight plan was completely dependent on the location of ground based stations.

Traditional navigation over land required airplanes to navigate from origin to destination by

receiving signals from ground-based navigation aids and flying over them one by one.

Navigation over remote or oceanic areas relied on either dead reckoning or self-contained

inertial navigation systems on the airplanes. Because of the navigational uncertainties inherent

in these traditional systems, large buffers were added to airways and procedures to provide safe

clearance of obstacles and terrain, as well as to maintain separation from airplanes in adjacent

airways.

RNAV refers to a navigational system that allows you to define your own way-points, where ever

you need them. This was done by different methods- inertial systems or systems that

automatically computed your position and course by using VOR and DME info These were also

used in combination. All of this was in use before the first GPS system was ever conceived.

In the 1980s, area navigation (RNAV) systems became widely available. Waypoints inthese systems are defined by simple latitude and longitude coordinates. These Earth-referenced waypoints allowed for the design of airways that did not reflect thegeographic, topographic, or political limitations governing the placement of navigationaids located on the ground. Airplanes with RNAV systems could file flight plans thatwere different from established airways or be given direct -to clearances, letting themdefine and fly their own unique airway that was the shortest distance between twopoints.

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Unfortunately, few airways or procedures were designed specifically for RNAV systems.

As a result, RNAV airplanes were reduced to emulating less capable non-RNAV

airplanes. The RNP concept enhances traditional RNAV system functionality and allows

a significant improvement over earlier methods of airspace design.

RNP

Required navigation performance (RNP) extends the capabilities of modernairplane navigation systems by providing real-time estimates of navigationuncertainty, assurance of performance through its containment concepts, andfeatures that ensure the repeatability and predictability of airplane navigation.This precise characterization of airplane performance is key to designing more

efficient airspace routes and procedures.

1. ICAO defined RNP as "a statement of the navigation performanceaccuracy necessary for operation within a defined airspace." Thisnavigation performance accuracy is quantified with two values: adistance in nautical miles (known as the RNP type) and a probabilitylevel. For example, an airplane is qualified to operate on an RNP 10airway if it has demonstrated that the capability and performance of theairplane navigation system will result in the airplane's being within 10nmi of the indicated position on the navigation system at least 95

percent of the flying time (fig. 1).
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1. The most powerful feature of the ICAO RNP concept is the specificationof a minimum performance requirement without equipment mandates.This is a major improvement over the previous method of derivingairspace design based on traditional discrete navigation systems or on abroad population of airplane navigation systems with widely varying

performance. However, other factors besides navigation performance(such as intervention capability, traffic density, and route structure) mustbe considered in determining the route separation reduction possiblewith ICAO RNP(fig. 2).

2. 2. INDUSTRY EXPANSION OF ICAO RNP3. While the ICAO definition of RNP adequately specified 95 percent

accuracy performance, it did not quantify other common navigationparameters normally used by industry during equipment design andcertification. It also lacked a way to statistically specify potential rareexcursions from the desired path. Two aviation standardsorganizationsthe U.S. Radio Technical Commission for Aeronautics(RTCA) and the European Organisation for Civil Aviation Equipment(EUROCAE)expanded the definition of RNP to include a new lateral

containment limit and minimum navigation system capabilities. Theseadditional requirements are documented in the "Minimum AviationSystem Performance Standards (MASPS): Required NavigationPerformance for Area Navigation," issued by the RTCA.

4. Lateral containment limit. The new containment limit specifies anadditional requirement on navigation system uncertainty beyond theICAO concept of 95 percent accuracy performance. The lateral (cross-
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track) dimension of this containment limit is twice the size of the RNPvalue and centered on the airplane's defined path(fig. 3).

5. The navigation system must ensure that the airplane remain within thiscontainment region 99.999 percent of the flight time. This outer linearcontainment region will be used to assess the safe separation ofairplanes and obstacle clearance when developing routes, areas, andprocedures.

6. Minimum navigation system capabilities. In addition to specifyingrequirements for continuity and availability of required positioningaccuracy, the MASPS specified capabilities to ensure consistency of

flight paths and operations across the fleet. For example, the types offlight plan legs that could make up RNP route segments were limitedand standardized to ensure that all similarly equipped airplanes flyconsistent and repeatable paths over the ground for a given airway orprocedure. Also specified in the MASPS was a real-time display of theestimated navigation system accuracy (called "estimated positionuncertainty" [EPU] or "actual navigation performance" [ANP] on Boeingcommercial airplanes). With an explicit display of EPU/ANP, the flightcrew can monitor trends while the navigation system automaticallychecks current performance against required performance (i.e., theRNP necessary for the operation). The system alerts the flight crewwhen performance is inadequate for the current operation.

This industry-expanded specification of RNP is called RNP RNAV to

differentiate it from the incomplete specification of RNP defined by ICAO. RNP

RNAV will be an aid in both separation and collision risk assessments for
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proposed routes and procedures. This will reduce route separation and

improve obstacle clearance limits beyond those provided by ICAO RNP(fig.

4).

Benefits include increased airspace capacity and efficiency, lower landing

minimums, and reduced workload, all of which contribute to improved safety

margins.
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Traditional and Area Navigation

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defined airspace. Ensured navigation performance and standardized functionality ofRNP allow new procedures to be designed for airports where infrastructure or terrainmakes it difficult or impossible to use some runways. RNP also allows for improvementsto procedures that are demanding on flight crews. Boeing has been a leader indeveloping national and international technical standards for RNP capability, which now

is available on all Boeing airplanes in production and in service.

Before introducing RNP operations into their fleets, operators shouldunderstand the following:

7. RNP as initially conceived by the International Civil AviationOrganization (ICAO).

8. Industry expansion of ICAO RNP.9. RNP capabilities on Boeing airplanes.10.Assessment of RNP capabilities.11.Operational approvals.12.1. RNP AS INITIALLY CONCEIVED BY THE INTERNATIONAL CIVIL

AVIATION ORGANIZATION13.In 1983, the ICAO formed the Future Air Navigation System (FANS)

Committee to develop a broad strategy that included new methods forairplane communication, navigation, and surveillance, and air trafficmanagement (CNS/ATM) (see "Operator Benefits of FANS" in Aero no.2, April 1998). The navigation element of CNS/ATM centers on theconcept of RNP. RNP provides for the specification of airspace based

on demonstrated levels of navigation performance and certain functionalcapabilities, rather than a required set of navigation sensors orequipment. Area navigation (RNAV) functionality is a key element of theRNP concept. (Area navigation systems define waypoints by latitudeand longitude coordinates and allow for navigation on any desired flightpath rather than one defined by ground-based radio beacons.See"Traditional and Area Navigation.")
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3. RNP CAPABILITIES ON BOEING AIRPLANES

RNP RNAV functionality is available on all Boeing commercial airplanes inproduction and can be retrofitted on Boeing models delivered without RNPcapability.

The MASPS established all significant aspects of navigation systemperformance, assurance, capability, and functionality that must be consideredfor RNP-based operations. Because many current systems will not meet every

MASPS requirement, any system deviations from the MASPS can bemitigated through limitations or operational procedures. This will allow asmany airplanes as possible to be qualified during the transition to RNPoperations. The Boeing RNP RNAV designs have addressed all the keyfunctional and performance requirements of the RNP MASPS. FurtherMASPS-compliant changes to Boeing designs most likely will be warranted byoperations and the evolution of RNP. Questions concerning MASPScompliance for specific models should be directed to Boeing Field Servicerepresentatives.

Boeing RNP functionality includes flight crew interface through a flightmanagement control display unit (CDU) and the airplane crew alerting system.Navigation, flight planning, and alerting algorithms are contained in theairplane flight management function(fig. 5).

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The CDU is used for flight plan and procedure selection and to display the

RNP for the active route segment and the current navigation performance (orANP). RNP values can be stored in the database for route segments,manually entered by the flight crew, or selected automatically, depending onthe flight phase(fig. 6).

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Annunciation to the flight crew occurs when the ANP exceeds RNP. Onairplanes with crew alerting systems (such as the 717, 747-400, 757, 767,777, and MD-90), a text message similar to UNABLE RNP is displayed in theappropriate area on the crew alerting message display. Other airplanes (suchas the 737 and MD-80) display the message on the CDU, the navigationdisplay, the primary flight display, or a combination of these.

4. ASSESSMENT OF RNP CAPABILITIES

Materials and references are available to help operators assess thecapabilities of Boeing RNP-equipped airplanes and to obtain regulatoryapproval to conduct RNP operations. The materials and references includethe Airplane Flight Manual (AFM) for each airplane, RNP capabilitydocuments, a Boeing document for an industry RNP RNAV workshop, a U.S.Federal Aviation Administration (FAA) RNP web site, and software forpersonal computers.

Airplane Flight Manual. The AFM is an information source on equipmentcertification and limitations approved by the FAA and other regulatory

authorities. The AFMs for Boeing airplanes certified for RNP RNAV capabilitycontain some or all of the following information:

The minimum demonstrated RNP as a function of the lateral flightcontrol mode. This is the smallest RNP value for which the airplaneequipment has been certified to operate at a given lateral control mode(e.g., the flight management system [FMS] lateral navigation with

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autopilot engaged). Values are provided for an active and inactiveglobal positioning system (GPS). This accommodates airplanes that donot use GPS to navigate and periods when satellite signals may not beavailable to support operations that require GPS to achieve the desiredlevel of RNP. The AFM notes that an RNP flight operation may be

subject to signal availability for both GPS and ground-based navigationaids (see the following section on RNP capability documents).

The minimum equipment required for RNP navigation. RNP values that provide airplane navigation performance equivalent to

traditional airplane navigation while conducting operations on currentapproaches that do not require RNP.

Explicit statements of compliance with regional RNP-related criteria.

RNP capability documents. These documents explain Boeing RNPimplementation as it relates to equipment certification and RNP operationalapprovals. They include the following (see table 1):

A detailed technical description of ANP, including ANP values that canbe expected, and when GPS and GPS coverage predictions may berequired for an RNP operation.

Automatic default RNP values and phase-of-flight logic. The concepts of required availability of navigation equipment and

navigation signals. Flight crew interface, including descriptions of RNP-related CDU page

displays and scratchpad text messages, flight crew alerts, andnavigation displays related to RNP and GPS navigation.

The availability of different levels of RNP to satisfy primary andsupplemental means of navigation.

Example applications of RNP for en route and terminal route separationand approach area obstacle clearance.

Discussion of the equivalency of RNP operations and values to existingcharted instrument approach procedures approved for non-RNP RNAV-equipped Boeing airplanes.

Derivation of the demonstrated minimum RNP values listed in the AFM.

5. OPERATIONAL APPROVALS

RNP operations. RNP operations gradually are being introducedaround the world on a regional or case-by-case basis. Operationsrequiring RNP capabilities are noted on the applicable airways andregional airspace documentation or procedure charts. These operationshave varying RNP functional and performance requirements. Some aremore consistent with ICAO RNP, which allows RNAV-equipped, non-
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RNP airplanes to be qualified to a level of RNP equivalency based onoriginally installed equipment, demonstrated performance, or both.Other operations require full RNP RNAV functionality.Table 2listssome initial regional approvals of RNP operations.

RNP RNAV operations. In most cases, RNP RNAV operations are

initiated by a few operators who have determined that their existingairplane RNP RNAV capabilities can provide operating efficiencies.

Achieving RNP RNAV operational approval requires operators to closelycoordinate with all interested parties, including airspace providers,regulatory agencies, and flight crew representatives. This ensures thatdecisions on route or procedure configuration, adjacent routeseparation, and obstruction clearance take into account importantfactors such as the availability and quality of surveillance,communications, the navigation infrastructure, traffic density, and airtraffic control procedures. In the future, when routes and procedures aredeveloped to RNP criteria, the regulatory authority responsible for anairline's operation will verify that RNP-capable airplanes meet the RNPrequirements for the operation.

SUMMARY

RNP allows airspace to be specified according to demonstrated airplane navigationperformance and certain airplane functional capabilities, rather than a required set ofnavigation sensors or equipment. RNAV functionality is a key element of the RNPconcept. Knowing in advance that airplanes can perform RNAV functions and achieve a

predetermined level of navigation performance allows for more optimal design ofairspace and procedures and eliminates the need to mandate specific equipment andsystems for airspace operations. RNP functionality exists on all Boeing productionairplanes and is available for retrofit on earlier models. Operators who choose toimplement RNP can benefit from improved safety of flight in their operations and accessto new, more efficient flight operations procedures.
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