Performance Based Navigation
Encyclopedia
ICAO performance-based navigation (PBN) represents a shift from sensor-based to performance-based navigation. PBN specifies that aircraft RNP and 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.
(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:
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
.
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.
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.
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.
These turns have two possible radii, 22.5 NM for high altitude routes (above FL
195) 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.
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.
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 performanceRequired Navigation Performance
Required Navigation Performance is a type of performance-based navigation that allows an aircraft to fly a specific path between two 3-dimensionally defined points in space. RNAV and RNP systems are fundamentally similar. The key difference between them is the requirement for on-board...
(RNP) specification. One not having such requirements is referred to as an area navigation
Area navigation
Area Navigation is a method of Instrument Flight Rules navigation that allows an aircraft to choose any course within a network of navigation beacons, rather than navigating directly to and from the beacons. This can conserve flight distance, reduce congestion, and allow flights into airports...
(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 VORVHF omnidirectional rangeVOR, short for VHF omnidirectional radio range, is a type of radio navigation system for aircraft. A VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice , and navigation signal. The identifier is typically a two- or three-letter string in Morse code...
can impact dozens of procedures, as a VOR can be used on routes, VOR approaches, missed approachMissed approachMissed approach is an instrument flight rules procedure which is a standard component segment of an instrument approach. Generally, if the pilot flying or the pilot in command determines by the time the aircraft is at the decision height or missed approach point , that the runway or its...
es, 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 (GRAS), while the introduction of Galileo and the modernisation of the Global Positioning System (GPS) and the Global Navigation Satellite SystemGLONASSGLONASS , acronym for Globalnaya navigatsionnaya sputnikovaya sistema or Global Navigation Satellite System, is a radio-based satellite navigation system operated for the Russian government by the Russian Space Forces...
(GLONASS) will further improve GNSS performance. The use of GNSS/inertialInertial navigation systemAn inertial navigation system is a navigation aid that uses a computer, motion sensors and rotation sensors to continuously calculate via dead reckoning the position, orientation, and velocity of a moving object without the need for external references...
integration is also expanding; - allows for more efficient use of airspaceAirspaceAirspace means the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere....
(route placement, fuel efficiency and noise mitigation); - clarifies how RNAV systems are used; and
- facilitates the operational approval process for civil aviation authoritiesCivil Aviation AuthorityThis is a list of national and supra-national civil aviation authorities.-See also:* Air route authority between the United States and the People's Republic of China* National Transportation Safety Board -External links:****...
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
Air traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
(ATC) environments, the navaid
Navigational aid
A navigational aid is any sort of marker which aids the traveler in navigation; the term is most commonly used to refer to nautical or aviation travel...
infrastructure and functional and operational capability needed to meet the ATM application. PBN performance requirements also depend on what reversion
Reversion (software development)
In software development , reversion or reverting is the abandonment of one or more recent changes in favor of a return to a previous version of the material at hand In software development (and by extension in content editing environments, especially wikis, that make use of the software development...
, 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
Next Generation Data Communications
Next Generation Data Communications, an element of the Next Generation Air Transportation System, will significantly reduce controller-to-pilot communications and controller workload, whilst improving safety.-Description:...
and enhanced surveillance functionality
Automatic dependent surveillance-broadcast
Automatic Dependent Surveillance-Broadcast is a surveillance technology for tracking aircraft as part of the Next Generation Air Transportation System ...
.
Impact on airspace planning
When separationSeparation (air traffic control)
In air traffic control, separation is the name for the concept of keeping an aircraft outside a minimum distance from another aircraft to reduce the risk of those aircraft colliding, as well as prevent accidents due to wake turbulence....
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
Distance Measuring Equipment
Distance measuring equipment is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals....
or NDB
Non-directional beacon
A non-directional beacon is a radio transmitter at a known location, used as an aviation or marine navigational aid. As the name implies, the signal transmitted does not include inherent directional information, in contrast to other navigational aids such as low frequency radio range, VHF...
. 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
Controlled airspace
Controlled airspace is an aviation term used to describe airspace in which ATChas the authority to control air traffic, the level of which varies with the different classes of airspace. Controlled airspace is established mainly for three different reasons:...
, 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.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 landingLanding
thumb|A [[Mute Swan]] alighting. Note the ruffled feathers on top of the wings indicate that the swan is flying at the [[Stall |stall]]ing speed...
operations with GNSS vertical guidance—approach procedure with vertical guidance APV-I and APV-II), as well as instrument landing system
Instrument Landing System
An instrument landing system is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument...
(ILS) and microwave landing system
Microwave landing system
A microwave landing system is an all-weather, precision landing system originally intended to replace or supplement instrument landing systems...
(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 if a navigation system complies with the necessary safety level associated with an RNP application; it relates to both lateralLNAV
Lateral navigation refers to navigating over a ground track with guidance from an electronic device which gives the pilot error indications in the lateral direction only and not in the vertical direction. In aviation lateral navigation is of two guidance types: linear guidance and angular guidance...
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
Airworthiness
Airworthiness is a term used to describe whether an aircraft has been certified as suitable for safe flight. Certification is initially conferred by a Certificate of Airworthiness from a National Airworthiness Authority, and is maintained by performing required maintenance actions by a licensed...
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 FL
Flight level
A Flight Level is a standard nominal altitude of an aircraft, in hundreds of feet. This altitude is calculated from the International standard pressure datum of 1013.25 hPa , the average sea-level pressure, and therefore is not necessarily the same as the aircraft's true altitude either...
195) 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 facilitiates the holdingHolding (aviation)
In aviation, holding is a maneuver designed to delay an aircraft already in flight while keeping it within a specified airspace.-Implementation:...
pattern specification by allowing the definition of the inbound course
Course (navigation)
In navigation, a vehicle's course is the angle that the intended path of the vehicle makes with a fixed reference object . Typically course is measured in degrees from 0° clockwise to 360° in compass convention . Course is customarily expressed in three digits, using preliminary zeros if needed,...
to the holding waypoint
Waypoint
A waypoint is a reference point in physical space used for purposes of navigation.-Concept:Waypoints are sets of coordinates that identify a point in physical space. Coordinates used can vary depending on the application. For terrestrial navigation these coordinates can include longitude and...
, 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.