Performance-based navigation

ICAO performance-based navigation (PBN) specifies that aircraft required navigation performance (RNP) and area navigation (RNAV) systems performance requirements be defined in terms of accuracy, integrity, availability, continuity, and functionality required for the proposed operations in the context of a particular airspace, when supported by the appropriate navigation infrastructure.^[1]

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the majesty of a jetliner gliding across the sky how magnificent is the sight how breathtaking is the technology and the ingenuity that transformed a simple invention into a lifestyle we know today as air travel and not just a lifestyle but a powerful engine that propels our economy forward. aviation generated 1.3 trillion dollars in travel and tourism 38.8 billion dollars for general aviation 10.5 million American jobs, 237.3 billion dollars from international travel and carries approximately forty percent of the value of all world goods. aviation demand is expected to grow tripling by some estimates and our skies and airports are already crowded with different types of aircraft and airspace users the aviation industry and government collaboratively strive to meet society's changing needs for aviation and national security how do we accommodate this growth while safeguarding our already high levels of safety at the same time achieving our commitments to diminish noise and environmental impacts how will we meet the public's need for safer more efficient and reliable air transportation how do we address the high costs of fuel with oil prices that now hover around one hundred dollars per barrel and how do we reduce environmental impacts and our carbon footprints how do we make technology work for us and how does it solve our problems the solutions provided by NextGen allow us to address these questions and begin to solve these challenges NextGen is modernization the movement to smart efficient technology and procedures let's start by looking at some of our nation's airports each with unique operational challenges and specific needs based on location Atlanta's Hartsfield-Jackson is the busiest airport in the world with multiple parallel runways a mix of aircraft types and operators and high traffic volumes compare that to New York's LaGuardia Airport with crossing runways very busy airspace and limited taxiways to maneuver, with limitations for expansion constrained by water and development Chicago's Midway Airport is an operational hub driven by short and closely spaced runways and noise-sensitive communities it also has complex and shared airspace interactions with Chicago's other major airport O'Hare Seattle represents an airport with growing operations and interest a new runway and associated procedure needs and challenges due to terrain weather interactions with the adjacent knowing airport operations these are just some of our airport airspace and environmental challenges and there's no one universal answer to solve them one of the most important safety and efficiency achievements to date is improving the way that aircraft can navigate one fundamental initiative of NextGen is to provide precise predictable and repeatable satellite navigation referred to as performance-based navigation or PBN there are two key components of PBN the first is area navigation or RNAV and the second is required navigation performance or RNP prior to PBN aircraft had to zig zag from one ground navigation station to another air traffic controllers needed to block large areas of air space around the aircraft to compensate for the variations in flight with RNAV aircraft fly more direct and optimized paths and air traffic controllers can block smaller amounts of airspace we get even more precise with RMP the aircraft is contained within a narrow corridor and the procedures can be designed with pinpoint predictable curve paths that provide even greater operational opportunities with PBN and procedures and repeatable curved paths we can improve flight efficiencies in all phases of flight let's explore how this NextGen initiative is helping to address the challenges of our congested skies and environmental concerns from departure through the on route to arrival and finally to the landing or approach phase the departure phase Atlanta's Hartsfield-Jackson International Airport where 10,000 RNAV flights now depart every week because aircraft no longer are restricted to fly over the ground systems and navigation precision is greatly increased we can create more departure exits or on ramps to fly into the on-route airspace this expedites aircraft away from our airports into the overhead streams efficiently for the airspace users the traveling public and the surrounding airport communities this translates into departure efficiencies which helps to reduce fuel time and emissions aircraft to part with minimal controller voice instructions greatly reducing the complexity and communications between the pilots and controllers so now we have the ability to create more on-ramps so how do we improve the use of our runways to allow the planes up in the air faster options are limited for adding more departure paths and runways the FAA is addressing this challenge by implementing new spacing standards based on the use of PBN for aircraft departing an airport today controllers launch successive aircraft on different courses or headings this is limiting and uses large portions of airspace the FAA's new standard in use today in Atlanta is called equivalent lateral spacing operations or ELSO and here's how it works using PBN procedures can be designed that use less airspace providing for additional departure paths from the runway ends that were otherwise not possible the added paths increase runway efficiency without putting the plane's any closer together at Atlanta this enables the controllers to handle the same traffic demand on two runways versus three NextGen is now seeking to expand this capability to other airports by developing a national standard the one thing about the ELSO initiative that stands out is of all the PBM procedures we've implemented at Atlanta this is bar none been the best one that we've done because everybody likes it the tower likes it because they get higher throughput the tray-con on likes it because we get to stay in RNAV all the time the airlines like it because they get higher throughput they get to stay on RNAV all the time It has no adverse impact on the center and it has not had adverse impact on the surrounding community as far as noise complaints go so it is bar none been the most successful PBN implementation we've ever had now let's look at the on route phase where aircraft are transitioning to and from our airports because we are free from the ground-based systems we can plan fly more direct and with optimize paths and better address restricted use airspace in some areas we need to expand the limited on-route road system into a highway system by adding routes where needed and otherwise not possible PBN enables us to fly optimized direct routes or multi-lane highways to serve multiple airports and connect high-volume metroplexes in the arrival phase as flights near their destinations we need to efficiently exit them from the on route or highway system as more exits or on-ramps are enabled for the departures likewise more exits or off-ramps are enabled for increased arrival efficiency PBN arrival procedures can be designed to allow the aircraft to descend efficiently by reducing or eliminating the need for level flight this design is called an optimized profile descent or OPD OPD's improve how the aircraft flies from higher altitudes down to the runway reducing engine noise saving gallons of fuel for aircraft and reducing carbon emissions so it helps to save fuel it helps have a smoother descent path and also is a quieter arrival for the neighbors we fly over it benefits the corporation from a cost perspective it benefits the community from the noise perspective And it benefits the environment missions in the approach phase our flight is coming in for a landing with more precise navigation for accurate incurred path approaches can be replace were needed in limited air space improving access and providing greater options to avoid challenging terrain or noise sensitive areas when possible the FAA and industry are working collaboratively on advanced RNP concepts that take advantage of the curve path and narrow containment to eliminate mileage costs impacts and improve access RNP also help to de-conflict adjacent airport traffic Interactions that cause flight disruptions in many metropolitan areas arrival and departure paths at nearby airports can interfere with each other this means that aircraft at one airport may be stopped on the ground or held in the air while aircraft at a nearby airport are landing or departing at Chicago O'Hare and Midway airports flight paths share the same airspace which result in costly delays cancellations and passenger disruptions a curved path RNP approach to Midway is designed to untangle the interaction at the two airports enabling uninterrupted operations the FAA has stepped up implementation of PBN across the National Airspace this is being achieved through collaborative industry airport and government teams for defining procedures and are high-volume and complex Metroplex airports with high projection benefits while abating environmental impact in order to measure progress in this effort the FAA is currently developing and testing a new PBN and analysis capability that uses sophisticated analysis methods to assess airport specific equipage report on procedure use in all phases of flight and to measure and report on the benefits of these new procedures by using improved reporting capabilities the FAA can better track usage of RNAV and RNP procedures and with this capability we can better evaluate where these changes are having impact and to make informed decisions for needed changes PBN is opening up new opportunities and solutions across the US and around the world thousands of procedures have been implemented to date advancing our aviation goals and our commitments for better in the global environment and the surrounding communities at our airports this is an exciting time for PBN and NextGen using innovative procedures that capitalize on current investments in technology along with developing new means to measure and monitor progress the FAA is building a performance-based navigational system to more safely and efficiently maximize this limited resource we call the National Airspace System

Description

Historically, aircraft navigation specifications have been specified directly in terms of sensors (navigation beacons and/or waypoints). A navigation specification that includes an additional requirement for on-board navigation performance monitoring and alerting is referred to as a required navigation performance (RNP) specification. One not having such requirements is referred to as an area navigation (RNAV) specification.

Performance requirements are identified in navigation specifications, which also identify the choice of navigation sensors and equipment that may be used to meet the performance requirements. The navigation specifications provide specific implementation guidance in order to facilitate global harmonisation.

Under PBN, generic navigation requirements are first defined based on the operational requirements. Civil aviation authorities then evaluate options in respect of available technology and navigation services. A chosen solution would be the most cost-effective for the civil aviation authority, as opposed to a solution being established as part of the operational requirements. 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.

PBN offers a number of advantages over the sensor-specific method of developing airspace and obstacle clearance criteria:

reduces the need to maintain sensor-specific routes and procedures, and their costs. For example, moving a single VOR can impact dozens of procedures, as a VOR can be used on routes, VOR approaches, missed approaches, etc. Adding new sensor-specific procedures would compound this cost, and the rapid growth in available navigation systems would soon make sensor-specific routes and procedures unaffordable;
avoids the need for developing sensor-specific operations with each new evolution of navigation systems, which would be cost-prohibitive. The expansion of satellite navigation services is expected to contribute to the continued diversity of RNP and RNAV systems in different aircraft. The original basic global navigation satellite system (GNSS) equipment is evolving due to the development of augmentations such as satellite-based augmentation systems (SBAS), ground-based augmentation systems (GBAS) and ground-based regional augmentation systems (GBAS), while the introduction of Galileo and the modernisation of the United States' Global Positioning System (GPS) and the Russian Global Navigation Satellite System (GLONASS) will further improve GNSS performance. The use of GNSS/inertial integration is also expanding;
allows for more efficient use of airspace (route placement, fuel efficiency and noise mitigation);
clarifies how RNAV systems are used; and
facilitates the operational approval process for civil aviation authorities by providing a limited set of navigation specifications intended for global use.

Within an airspace, PBN requirements will be affected by the communication, surveillance and air traffic control (ATC) environments, the navaid infrastructure and functional and operational capability needed to meet the ATM application. PBN performance requirements also depend on what reversion, non-RNAV means of navigation are available and what degree of redundancy is required to ensure adequate continuity of operations.

To achieve the efficiency and capacity gains partially enabled by RNAV and RNP, the FAA will pursue use of data communications and enhanced surveillance functionality.^[2]

Background

Area navigation techniques and specifications started to evolve regionally without overall ICAO guidance. This consequently meant that terms and definitions such as "RNAV" and "RNP" had slightly different meanings in different regions of the world, and even other terms could be used locally. An example of this is the term "P-RNAV" (Precision RNAV) that Europe still uses (2019), which elsewhere is called "RNAV 1".

The terms RNAV and RNP was earlier used with little functional difference. RNP required a certain level of performance but made no attempt to define how it was to be guaranteed.

Performance-based navigation (PBN) is ICAO's initiative to standardise terminology, specifications and meanings. One example is to standardise the terminology used around APVs (Approaches with vertical guidance). All APVs have until recently been designated as RNAV-approaches, while these in fact are RNP-approaches with respect to the PBN implementation. All APVs require on-board performance monitoring and alerting, so the system cannot only be capable of navigation down to the required degree of accuracy, but also needs to continuously monitor the performance and be capable of alerting the pilot if its performance falls below that which is required.

These approaches had some confusing names and designations on charts, and the changeover is currently being conducted across all member states. The two types of RNAV-approaches have traditionally been named RNAV (GNSS) and RNAV (RNP) respectively, where the former is the traditional straight-in approach from the final approach fix, and the latter is a more complex approach that curves in the horizontal plane after the final approach fix which requires authorization for it to be commenced (AR = Authorization Required). The correct naming and designation for these approaches under the PBN implementation are RNP and RNP AR respectively. The images to the right show the naming of the current charts being used, and what they will look like under PBN. ^[3]

Impact on airspace planning

When separation minima and route spacing are determined using a conventional sensor-based approach, the navigation performance data used to determine the separation minima or route spacing depend on the accuracy of the raw data from specific navigation aids such as VOR, DME or NDB. In contrast, PBN requires an RNAV system that integrates raw navigation data to provide a positioning and navigation solution. In determining separation minima and route spacing, this integrated navigation performance "output" is used.

The navigation performance required from the RNAV system is part of the navigation specification. To determine separation minima and route spacing, airspace planners fully exploit that part of the navigation specification which describes the performance required from the RNAV system. Airspace planners also make use of the required performance (accuracy, integrity, availability and continuity) to determine route spacing and separation minima.

In procedurally controlled airspace, separation minima and route spacing on RNP specifications are expected to provide a greater benefit than those based on RNAV specifications. This is because the on-board performance monitoring and alerting function could alleviate the absence of ATS surveillance service by providing an alternative means of risk mitigation.

Transition to PBN

It is expected that all future RNAV and RNP applications will identify the navigation requirements through the use of performance specifications rather than defining specific navigation sensors.

The Valley of Mexico will be the first in Mexico where the performance-based navigation system is used, which will allow the new Felipe Ángeles International Airport, the Mexico City International Airport, and the Toluca International Airport to operate simultaneously without the operations of one impeding those of the others.^[4]

Scope

For legacy reasons associated with the previous RNP concept, PBN is currently limited to operations with linear lateral performance requirements and time constraints. For this reason, operations with angular lateral performance requirements (i.e. approach and landing operations with GNSS vertical guidance—approach procedure with vertical guidance APV-I and APV-II), as well as instrument landing system (ILS) and microwave landing system (MLS) are not considered. Unlike the lateral monitoring and obstacle clearance, for barometric VNAV systems there is neither alerting on vertical error nor is there a two-times relationship between a 95% required total system accuracy and the performance limit. Therefore, barometric VNAV is not considered vertical RNP.

On-board performance monitoring and alerting

On-board performance monitoring and alerting is the main element that determines whether a navigation system complies with the required safety level associated with an RNP application. It relates to both lateral and longitudinal navigation performance; and it allows the aircrew to detect that the navigation system is not achieving, or cannot guarantee with 10⁻⁵ integrity, the navigation performance required for the operation.

RNP systems provide improvements on the integrity of operations. This may permit closer route spacing and can provide sufficient integrity to allow only RNAV systems to be used for navigation in a specific airspace. The use of RNP systems may therefore offer significant safety, operational and efficiency benefits.

On-board performance monitoring and alerting capabilities fulfill two needs, one on board the aircraft and one within the airspace design. The assurance of airborne system performance is implicit for RNAV operations. Based upon existing airworthiness criteria, RNAV systems are only required to demonstrate intended function and performance using explicit requirements that are broadly interpreted. The result is that while the nominal RNAV system performance can be very good, it is characterised by the variability of the system functionality and related flight performance. RNP systems provide a means to minimise variability and assure reliable, repeatable and predictable flight operations.

On-board performance monitoring and alerting allow the air crew to detect whether or not the RNP system satisfies the navigation performance required in the navigation specification. On-board performance monitoring and alerting relate to both lateral and longitudinal navigation performance.

On-board performance monitoring and alerting is concerned with the performance of the area navigation system.

"on-board" explicitly means that the performance monitoring and alerting is affected on board the aircraft and not elsewhere, e.g. using a ground-based route adherence monitor or ATC surveillance. The monitoring element of on-board performance monitoring and alerting relates to flight technical error (FTE) and navigation system error (NSE). Path definition error (PDE) is constrained through database integrity and functional requirements on the defined path, and is considered negligible.
"monitoring" refers to the monitoring of the aircraft's performance as regards its ability to determine positioning error and/or to follow the desired path.
"alerting" relates to the monitoring: if the aircraft's navigation system does not perform well enough, this will be alerted to the air crew.

RNAV and RNP specific functions

Performance-based flight operations are based on the ability to assure reliable, repeatable and predictable flight paths for improved capacity and efficiency in planned operations. The implementation of performance-based flight operations requires not only the functions traditionally provided by the RNAV system, but also may require specific functions to improve procedures, and airspace and air traffic operations. The system capabilities for established fixed radius paths, RNAV or RNP holding, and lateral offsets fall into this category.

Fixed radius paths

Fixed radius paths (FRP) take two forms:

the radius to fix (RF) leg type 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. Bank angle limits for different aircraft types and winds aloft are taken into account in procedure design.
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 FL195) and 15 NM for low altitude routes. Using such path elements in an RNAV route enables improvement in airspace usage through closely spaced parallel routes.

Fly-by turns

Fly-by turns are a key characteristic of an RNAV flight path. The RNAV system uses information on aircraft speed, bank angle, wind and track angle change to calculate a flight path turn that smoothly transitions from one path segment to the next. However, because the parameters affecting the turn radius can vary from one plane to another, as well as due to changing conditions in speed and wind, the turn initiation point and turn area can vary.

Holding pattern

The RNAV system facilitates the holding pattern specification by allowing the definition of the inbound course to the holding waypoint, turn direction and leg time or distance on the straight segments, as well as the ability to plan the exit from the hold. For RNP systems, further improvement in holding is available. These RNP improvements include fly-by entry into the hold, minimising the necessary protected airspace on the non-holding side of the holding pattern, consistent with the RNP limits provided. Where RNP holding is applied, a maximum of RNP 1 is suggested since less stringent values adversely affect airspace usage and design.

Offset flight path

RNAV systems may provide the capability for the flight crew to specify a lateral offset from a defined route. Generally, lateral offsets can be specified in increments of 1 NM up to 20 NM. When a lateral offset is activated in the RNAV system, the RNAV aircraft will depart the defined route and typically intercept the offset at a 45° or less angle. When the offset is cancelled, the aircraft returns to the defined route in a similar manner. Such offsets can be used both strategically i.e. fixed offset for the length of the route, or tactically i.e. temporarily. Most RNAV systems discontinue offsets in the terminal area or at the beginning of an approach procedure, at an RNAV hold, or during course changes of 90° or greater.

Minimum navigation performance specifications

Aircraft operating in the North Atlantic airspace are required to meet a minimum navigation performance specification (MNPS). The MNPS specification has intentionally been excluded from PBN because of its mandatory nature and because future MNPS implementations are not envisaged.^[5]

Future developments

It is likely that navigation applications will progress from 2-dimensional to 3-dimensional/4-dimensional applications, although time-scales and operational requirements are currently difficult to determine. Consequently, on-board performance monitoring and alerting is still to be developed in the vertical plane (vertical RNP) and ongoing work is aimed at harmonising longitudinal and linear performance requirements. Angular performance requirements associated with approach and landing will be included in the scope of PBN in the future. Similarly, specifications to support helicopter-specific navigation and holding functional requirements may also be included.

References

^ ICAO. Doc 9613, Performance-based Navigation (PBN) Manual, 2008. ISBN 978-92-9231-198-8
^ FAA. Roadmap for Performance-Based Navigation: Evolution for Area Navigation (RNAV) and Required Navigation Performance (RNP) Capabilities 2006-2025. 2006.
^ "What Are PBN". About Domain. 23 June 2023. Retrieved 19 May 2023.
^ Eduardo Murillo (Jan 29, 2020). "Tendrá tecnología de punta el aeropuerto de Santa Lucía" [The Santa Lucia airport will have cutting-edge technology]. La Jornada (in Spanish). Retrieved Jan 30, 2020.
^ The requirements for MNPS are set out in the Consolidated Guidance and Information Material concerning Air Navigation in the North Atlantic Region (NAT Doc 001) (available at [1])

External links

Boeing. Operational Benefits of Performance-Based Navigation 2008.

This article incorporates public domain material from websites or documents of the Federal Aviation Administration.

This page was last edited on 6 March 2024, at 04:44

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