REQUIRED NAVIGATION PERFORMANCE FOR IMPROVED FLIGHT OPERATIONS AND EFFICIENT USE OF AIRSPACE

RNP 12 ➔ 4

RNP 10 ➔ 4

RNP 5 ➔ 1

RNP 10 ➔ 4

RNP 4

RNP 10 ➔ 4JEFF AIMAR

ASSOCIATE TECHNICAL FELLOW

AIR TRAFFIC MANAGEMENT SERVICES

BOEING COMMERCIAL AIRPLANES GROUP

FLIGHT OPERATIONS

AERO

26

RNP 4

RNP 0.3 ➔ 0.1

RNP

RNP

2 x RNP

2 x RNP

AERO

29AERO

28

equired navigation per-formance (RNP) extends the capabilities of modern

airplane navigation systems by providing real-time estimates ofnavigation uncertainty, assurance of performance through its con-tainment concepts, and featuresthat ensure the repeatability andpredictability of airplane naviga-tion. This precise characterizationof airplane performance is key todesigning more efficient airspaceroutes and procedures.

Before introducing RNP operationsinto their fleets, operators shouldunderstand the following:

1. RNP as initially conceived by the International CivilAviation Organization (ICAO).

2. Industry expansion of ICAO RNP.

3. RNP capabilities on Boeing airplanes.

4. Assessment of RNP capabilities.

5. Operational approvals.

RNP AS INITIALLY CONCEIVED BY THE INTERNATIONAL CIVILAVIATION ORGANIZATION

In 1983, the ICAO formed the Future Air Navigation System (FANS)Committee to develop a broad strategythat included new methods for airplanecommunication, navigation, and sur-veillance, and air traffic management(CNS/ATM) (see “Operator Benefits ofFANS” in Aero no. 2, April 1998). Thenavigation element of CNS/ATM centerson the concept of RNP. RNP providesfor the specification of airspace basedon demonstrated levels of navigationperformance and certain functionalcapabilities, rather than a required setof navigation sensors or equipment.Area navigation (RNAV) functionality is a key element of the RNP concept.(Area navigation systems define waypoints by latitude and longitudecoordinates and allow for navigationon any desired flight path rather thanone defined by ground-based radio

beacons. See “Traditional and AreaNavigation” on p. 34.)

ICAO defined RNP as “a statement ofthe navigation performance accuracynecessary for operation within adefined airspace.” This navigation performance accuracy is quantifiedwith two values: a distance in nauticalmiles (known as the RNP type) and a probability level. For example, anairplane is qualified to operate on anRNP 10 airway if it has demonstratedthat the capability and performance of the airplane navigation system willresult in the airplane’s being within 10 nmi of the indicated position on the navigation system at least 95 percent of the flying time (fig. 1).

The most powerful feature of the ICAORNP concept is the specification of aminimum performance requirement with-out equipment mandates. This is a majorimprovement over the previous methodof deriving airspace design based on traditional discrete navigation systems or on a broad population of airplane navigation systems with widely varyingperformance. However, other factorsbesides navigation performance (such asintervention capability, traffic density,and route structure) must be consideredin determining the route separationreduction possible with ICAO RNP (fig. 2).

INDUSTRY EXPANSION OF ICAO RNP

While the ICAO definition of RNPadequately specified 95 percent accuracyperformance, it did not quantify othercommon navigation parameters normallyused by industry during equipment designand certification. It also lacked a way tostatistically specify potential rare excur-sions from the desired path. Two aviation standards organizations—the U.S. Radio

Technical Commission for Aeronautics(RTCA) and the European Organisation forCivil Aviation Equipment (EUROCAE)—expanded the definition of RNP to includea new lateral containment limit and minimum navigation system capabilities.These additional requirements aredocumented in the “Minimum AviationSystem Performance Standards (MASPS):Required Navigation Performance for Area Navigation,” issued by the RTCA.

2

1

The aviation industry projects that increasing demandson airspace will result in more air travel delays andrelated costs, unless the traditional system of airplanenavigation, monitoring, and control is changed. Inresponse, a new tool, called required navigation per-formance (RNP), is being developed that will be a keyelement in reducing en route airplane separation and,as a result, increase airspace capacity. This tooldefines the navigation accuracy an airplane must haveto operate within a defined airspace. Ensured naviga-tion performance and standardized functionality of RNP allow new procedures to be designed for airportswhere infrastructure or terrain makes it difficult orimpossible to use some runways. RNP also allows forimprovements to procedures that are demanding onflight crews. Boeing has been a leader in developingnational and international technical standards for RNP capability, which now is available on all Boeingairplanes in production and in service.

Actual airplane location within 10 nmi of navigation system position at least 95% of flight time

10 nmi

10 nmi

10 nmi 10 nmi

Desired path (airway)

RNP

RNP

RNP RNP

Mitigates navigation errors, route structure, traffic density, surveillance, ATC, communication

10 nmi

60 to 100 nmiMitigates navigation errors,

navigation performance, route structure, traffic density, sur-veillance, ATC, communication

POPP

Pre-RNP

PLWX

PWVG

PLMNRNP

Navigation performance

5 x RNP, 6 x RNP(50 to 60 nmi)

RNP leads to reduced buffers for route spacing and increased traffic capacity in the same airspace.

Legend:

Desired pathRNP 95% threshold

R

2 ICAO RNP AIRSPACE BUFFER REDUCTION

FIGURE

1 ICAO RNP 10 EXAMPLE

FIGURE

Mitigates navigation errors, route structure, traffic density, surveillance, ATC, communication

4 nmi

Note: Optimal case shown. Some buffer may be needed to mitigate nonoptimal communications surveillance or high density.

PWVG

PLMNRNP RNP 4 RNAV

5 x RNP, 6 x RNP(20 to 24 nmi)

Performanceassuranceregion

4 x RNP(16 nmi)

PWVG

4 nmi

8 nmi

PLMN

RNP RNAV is a tool to facilitate further optimization(reduction) in airspace buffers.

Legend:

Defined pathRNP 95% thresholdContainment limit

AERO

31AERO

30

Lateral containment limit. The newcontainment limit specifies an addi-tional requirement on navigation system uncertainty beyond the ICAOconcept of 95 percent accuracy performance. The lateral (cross-track)dimension of this containment limit is twice the size of the RNP value andcentered on the airplane’s defined path(fig. 3). The navigation system mustensure that the airplane remain withinthis containment region 99.999 percentof the flight time. This outer linearcontainment region will be used toassess the safe separation of airplanesand obstacle clearance when develop-ing routes, areas, and procedures.

Minimum navigation system capabilities. In addition to specifyingrequirements for continuity and avail-ability of required positioning accuracy,the MASPS specified capabilities toensure consistency of flight paths and operations across the fleet. Forexample, the types of flight plan legsthat could make up RNP route seg-ments were limited and standardized to ensure that all similarly equipped airplanes fly consistent and

repeatable paths over the ground for a given airway or procedure. Also specified in the MASPS was a real-timedisplay of the estimated navigation system accuracy (called “estimatedposition uncertainty” [EPU] or “actualnavigation performance” [ANP] onBoeing commercial airplanes). With an explicit display of EPU/ANP, theflight crew can monitor trends whilethe navigation system automaticallychecks current performance againstrequired performance (i.e., the RNPnecessary for the operation). The system alerts the flight crew whenperformance is inadequate for the current operation.

This industry-expanded specificationof RNP is called RNP RNAV to differen-tiate it from the incomplete specifi-cation of RNP defined by ICAO. RNPRNAV will be an aid in both separa-tion and collision risk assessments for proposed routes and procedures.This will reduce route separation andimprove obstacle clearance limitsbeyond those provided by ICAO RNP(fig. 4). Benefits include increased airspace capacity and efficiency,

lower landing minimums, and reducedworkload, all of which contribute toimproved safety margins.

RNP CAPABILITIES ON BOEING AIRPLANES

RNP RNAV functionality is available on all Boeing commercial airplanes inproduction and can be retrofitted onBoeing models delivered withoutRNP capability.

The MASPS established all signifi-cant aspects of navigation system performance, assurance, capability, andfunctionality that must be consideredfor RNP-based operations. Becausemany current systems will not meetevery MASPS requirement, any systemdeviations from the MASPS can be mitigated through limitations or operational procedures. This will allowas many airplanes as possible to be qualified during the transition to RNPoperations. The Boeing RNP RNAVdesigns have addressed all the key func-tional and performance requirementsof the RNP MASPS. Further MASPS-compliant changes to Boeing designsmost likely will be warranted by operations and the evolution of RNP.Questions concerning MASPS compliancefor specific models should be directedto Boeing Field Service representatives.

Boeing RNP functionality includesflight crew interface through a flightmanagement control display unit(CDU) and the airplane crew alertingsystem. Navigation, flight planning,and alerting algorithms are containedin the airplane flight managementfunction (fig. 5).

The CDU is used for flight plan andprocedure selection and to display theRNP for the active route segment andthe current navigation performance (orANP). RNP values can be stored in thedatabase for route segments, manuallyentered by the flight crew, or selectedautomatically, depending on the flightphase (fig. 6).

Annunciation to the flight crewoccurs 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 simi-lar to UNABLE RNP is displayed in the

appropriate area on the crew alertingmessage display. Other airplanes (such as the 737 and MD-80) displaythe message on the CDU, the naviga-tion display, the primary flight display,or a combination of these.

ASSESSING RNP CAPABILITIES

Materials and references are availableto help operators assess the capabili-ties of Boeing RNP-equipped airplanesand to obtain regulatory approval toconduct RNP operations. The materialsand references include the AirplaneFlight Manual (AFM) for each airplane,RNP capability documents, a Boeingdocument for an industry RNP RNAVworkshop, a U.S. Federal AviationAdministration (FAA) RNP Web site,and software for personal computers.

Airplane Flight Manual. The AFM isan information source on equipment

certification and limitations approvedby the FAA and other regulatoryauthorities. The AFMs for Boeing airplanes certified for RNP RNAV capability contain some or all of thefollowing information:

■ The minimum demonstrated RNP as a function of the lateral flightcontrol mode. This is the smallestRNP value for which the airplaneequipment has been certified tooperate at a given lateral controlmode (e.g., the flight managementsystem [FMS] lateral navigationwith autopilot engaged). Valuesare provided for an active andinactive global positioning system(GPS). This accommodatesairplanes that do not use GPS tonavigate and periods when satel-lite signals may not be availableto support operations that requireGPS to achieve the desired level ofRNP. The AFM notes that an RNP

3

4

4 RNP 4 RNAV EXAMPLE

FIGURE

RNP: 95% 2 x RNP

RNP

Containment limit

Containment limit: 99.999%

■ RNP RNAV is referenced to the airplane defined path

■ ICAO RNP is referenced to the airspace desired path

Defined pathDesired path

3 RNP RNAV CONTAINMENT

FIGURE

5 RNP SYSTEM SCHEMATIC

FIGURE

AERO

32AERO

33

flight operation may be subject to signal availability for both GPSand ground-based navigation aids(see the following section on RNPcapability documents).

■ The minimum equipment requiredfor RNP navigation.

■ RNP values that provide airplanenavigation performance equivalentto traditional airplane navigationwhile conducting operations oncurrent approaches that do notrequire RNP.

■ Explicit statements of compliancewith regional RNP-related criteria.

RNP capability documents. Thesedocuments explain Boeing RNP imple-mentation as it relates to equipmentcertification and RNP operationalapprovals. They include the following(see table 1):

■ A detailed technical description of ANP, including ANP values thatcan be expected, and when GPSand GPS coverage predictions maybe required for an RNP operation.

■ Automatic default RNP values andphase-of-flight logic.

■ The concepts of required avail-ability of navigation equipmentand navigation signals.

■ Flight crew interface, includingdescriptions of RNP-related CDU

page displays and scratch-pad textmessages, flight crew alerts, andnavigation displays related to RNP and GPS navigation.

■ The availability of different levelsof RNP to satisfy primary and supplemental means of navigation.

■ Example applications of RNP for en route and terminal route separation and approach areaobstacle clearance.

■ Discussion of the equivalency of RNP operations and values toexisting charted instrumentapproach procedures approved fornon-RNP RNAV-equipped Boeingairplanes.

■ Derivation of the demonstrated mini-mum RNP values listed in the AFM.

Boeing document for an industry RNP RNAV workshop. A Boeing Web site offers access to the following document on RNP and RNAV opertions:“FMS RNAV Workshop—GeneralInformation on the Functional andTechnical Aspects of RequiredNavigation Performance (RNP) AreaNavigation (RNAV) and Applications”(http://www.boeing.com/commercial/caft/reference/documents/RNP.pdf).

FAA RNP Web site. This site pre-sents a variety of information onexisting programs to implement RNP(http://www.faa.gov/ats/ato/rnp.htm).

Flight Procedures Standards Branch Web site. The FAA’s vision for implementing RNP in the U.S.national airspace is explained on thissite (http://www.mmac.jccbi.gov/afs/afs420/OutReach/index.htm).

European Organisation for the Safetyof Air Navigation (EUROCONTROL) Web site. Of special interest are the Terminal Area RNAV Applicationssubgroup and the “EUROCONTROLStandard Document for Area NavigationEquipment—Operational Requirementsand Functional Requirements.”This document is available through the document library on the Web site(http://www.ecacnav.com/default.htm).

Software for personal computers.Several software applications are available from vendors of GPS receiversthat can help operators determinewhether adequate GPS signal coverage is available for an RNP flight operation.Contact the vendors for copies.

OPERATIONAL APPROVALS

RNP operations. RNP operations gradually are being introduced aroundthe world on a regional or case-by-casebasis. Operations requiring RNP capa-bilities are noted on the applicable airways and regional airspace docu-mentation or procedure charts. Theseoperations have varying RNP functionaland performance requirements. Some are more consistent with ICAO RNP,which allows RNAV-equipped, non-RNP airplanes to be qualified to a level of RNP equivalency based on originallyinstalled equipment, demonstrated performance, or both. Other operationsrequire full RNP RNAV functionality.Table 2 lists some initial regionalapprovals of RNP operations.

RNP RNAV operations. In most cases,RNP RNAV operations are initiated by a few operators who have determinedthat their existing airplane RNP RNAVcapabilities can provide operating efficiencies. Achieving RNP RNAV operational approval requires operatorsto closely coordinate with all interestedparties, including airspace providers, regulatory agencies, and flight crew

6 CDU POSITION REFERENCE PAGE

FIGURE

5

RNP value

RNP 4

RNP 5

RNP 10

RNP 12.6

RNP 0.15 ➔ 0.30

Type

ICAO

ICAO

ICAO

ICAO

RNP/RNAV

Region

Japan

Europe

Pacific

North Atlantic

Alaska (special approval)

2 REGIONAL APPROVALSOF RNP OPERATIONS

TABLE

Model

737-300/-400/-500/-600/-700/-800

747-400

757/767

777

Documents are available at the following Boeing Web site:http://www.boeing.com/commercial/caft/reference/documents/newdocs.htm

Document number

D6-39067-2

D926U050

D926T0120

D243W018-7

1 RNP CAPABILITY DOCUMENTS

TABLE

SUMMARYRNP allows airspace to be specified according to demonstrated airplane navigation performance and certain airplane functional capabilities, rather than a required set of navigation 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 of airspace and procedures and eliminates the need to mandate specific equipment andsystems for airspace operations. RNP functionality exists on all Boeing production airplanes and is available for retrofit on earlier models. Operators who choose to implement RNP can benefit from improved safety of flight in their operations andaccess to new, more efficient flight operations procedures.

FOR DETAILS ON RNP RETROFITS, CONTACT BOEING AIRPLANE SERVICES.

Phone: 425-865-7950

Fax: 425-865-7896

E-mail: airplaneservices@boeing.com

Address: P.O. Box 3707 MC 7R-72 Seattle, WA 98124-2207 USA

FOR ASSISTANCE WITH RNP PROCEDURES, CONTACT BOEING AIR TRAFFIC MANAGEMENT SERVICES.

Phone: 206-662-8500

Fax: 206-662-8688

E-mail: david.l.allen@boeing.com

Address: P.O. Box 3707 MC 29-09 Seattle, WA 98124-2207 USAAttention: David L. Allen

representatives. This ensures that decisions on route or procedure configuration, adjacent route separa-tion, and obstruction clearance take into account important factors such asthe availability and quality of surveil-lance, communications, the navigationinfrastructure, traffic density, and airtraffic control procedures. In the future,when routes and procedures are devel-oped to RNP criteria, the regulatoryauthority responsible for an airline’soperation will verify that RNP-capableairplanes meet the RNP requirements for the operation.