Area navigation
Encyclopedia
Area Navigation is a method of Instrument Flight Rules
(IFR) 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 airport
s without beacons. Area navigation used to be called Random Navigation and therefore the acronym is RNAV .
RNAV can be defined as a method of navigation
that permits aircraft operation on any desired course within the coverage of station-referenced navigation signals or within the limits of a self-contained system capability, or a combination of these.
In the United States
, RNAV was developed in the 1960s, and the first such routes were
published in the 1970s. In January 1983, the Federal Aviation Administration
revoked all contiguous United States
RNAV routes due to findings that aircraft were using inertial navigation system
s rather than the ground-based beacons http://www.epa.gov/EPA-IMPACT/2003/May/Day-09/i11638.htm. RNAV was reanimated after the large-scale introduction of satellite navigation
.
capacity, thus emphasizing the need for optimum utilisation of available airspace. Improved operational efficiency derived from the application of area navigation techniques has resulted in the development of navigation applications in various regions worldwide and for all phases of flight. These applications could potentially be expanded to provide guidance for ground movement operations.
Requirements for navigation applications on specific routes or within a specific airspace must be defined in a clear and concise manner. This is to ensure that the flight crew
and the air traffic controller
s are aware of the on-board RNAV system capabilities in order to determine if the performance of the RNAV system is appropriate for the specific airspace requirements.
RNAV systems evolved in a manner similar to conventional ground-based routes and procedures. A specific RNAV system was identified and its performance was evaluated through a combination of analysis and flight test
ing. For land-based operations, the initial systems used very high frequency omnidirectional radio range
(VOR) and distance measuring equipment
(DME) for estimating position; for oceanic operations, inertial navigation system
s (INS) were employed. Airspace and obstacle clearance
criteria were developed based on the performance of available equipment, and specifications for requirements were based on available capabilities. Such prescriptive requirements resulted in delays to the introduction of new RNAV system capabilities and higher costs for maintaining appropriate certification. To avoid such prescriptive specifications of requirements, an alternative method for defining equipment requirements has been introduced. This enables the specification of performance requirements, independent of available equipment capabilities, and is termed performance-based navigation
(PBN). Thus, RNAV is now one of the navigation techniques of PBN; currently the only other is required navigation performance
(RNP).
RNAV and RNP systems are fundamentally similar. The key difference between them is the requirement for on-board performance monitoring and alerting. A navigation specification that includes a requirement for on-board navigation performance monitoring and alerting is referred to as an RNP specification. One not having such requirements is referred to as an RNAV specification. An area navigation system capable of achieving the performance requirement of an RNP specification is referred to as an RNP system.
As a result of decisions made in the industry in the 1990s, most modern RNAV systems provide on-board performance monitoring and alerting, therefore the navigation specifications developed for use by these systems can be designated as RNP.
Many RNAV systems, while offering very high accuracy and possessing many of the functions provided by RNP systems, are not able to provide assurance
of their performance. Recognising this, and to avoid operators incurring unnecessary expense, where the airspace requirement does not necessitate the use of an RNP system, many new as well as existing navigation requirements will continue to specify RNAV rather than RNP systems. It is therefore expected that RNAV and RNP operations will co-exist for many years.
However, RNP systems provide improvements in the integrity of operation, permitting possibly closer route spacing, and can provide sufficient integrity to allow only the RNP systems to be use for navigation in a specific airspace. The use of RNP systems may therefore offer significant safety, operational and efficiency benefits. While RNAV and RNP applications will co-exist for a number of years, it is expected that there will be a gradual transition to RNP applications as the proportion of aircraft equipped with RNP systems increases and the cost of transition reduces.
accuracy may be due to navigation errors related to aircraft tracking and positioning. The three main errors are path definition error (PDE), flight technical error (FTE) and navigation system error (NSE). The distribution of these errors is assumed to be independent, zero-mean
and Gaussian. Therefore, the distribution of total system error (TSE) is also Gaussian with a standard deviation
equal to the root sum square
(RSS) of the standard deviations of these three errors.
PDE occurs when the path defined in the RNAV system does not correspond to the desired path, i.e. the path expected to be flown over the ground. Use of an RNAV system for navigation presupposes that a defined path representing the intended track is loaded into the navigation database. A consistent, repeatable path cannot be defined for a turn that allows for a fly-by turn at a waypoint (because nearness to waypoint and wind vector
may not be repeatable), requires a fly-over of a waypoint (because wind vector may not be repeatable), or occurs when the aircraft reaches a target altitude
(because target altitude is dependent on engine thrust
and aircraft weight). In these cases, the navigation database contains a point-to-point desired flight path, but cannot account for the RNAV system defining a fly-by or fly-over path and performing a manoeuvre. A meaningful PDE and FTE cannot be established without a defining path, resulting in variability in the turn. Also, a deterministic, repeatable path cannot be defined for paths based on heading and the resulting path variability is accommodated in the route design.
FTE relates to the air crew or autopilot
's ability to follow the defined path or track, including any display error (e.g. course deviation indicator
(CDI) centring error). FTE can be monitored by the autopilot or air crew procedures and the extent to which these procedures need to be supported by other means depends, for example, on the phase of flight (i.e. take-off
, climb
, cruise
, descent
, landing
) and the type of operations. Such monitoring support could be provided by a map display.
NSE refers to the difference between the aircraft's estimated position and actual position.
There are no RNAV approach specifications.
Instrument flight rules
Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....
(IFR) navigation that allows an aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
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 airport
Airport
An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...
s without beacons. Area navigation used to be called Random Navigation and therefore the acronym is RNAV .
RNAV can be defined as a method of navigation
Navigation
Navigation is the process of monitoring and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks...
that permits aircraft operation on any desired course within the coverage of station-referenced navigation signals or within the limits of a self-contained system capability, or a combination of these.
In the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, RNAV was developed in the 1960s, and the first such routes were
published in the 1970s. In January 1983, the Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
revoked all contiguous United States
Contiguous United States
The contiguous United States are the 48 U.S. states on the continent of North America that are south of Canada and north of Mexico, plus the District of Columbia....
RNAV routes due to findings that aircraft were using inertial navigation system
Inertial navigation system
An 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...
s rather than the ground-based beacons http://www.epa.gov/EPA-IMPACT/2003/May/Day-09/i11638.htm. RNAV was reanimated after the large-scale introduction of satellite navigation
Global Navigation Satellite System
A satellite navigation or SAT NAV system is a system of satellites that provide autonomous geo-spatial positioning with global coverage. It allows small electronic receivers to determine their location to within a few metres using time signals transmitted along a line-of-sight by radio from...
.
Background
The continuing growth of aviation increases demands on airspaceAirspace
Airspace 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....
capacity, thus emphasizing the need for optimum utilisation of available airspace. Improved operational efficiency derived from the application of area navigation techniques has resulted in the development of navigation applications in various regions worldwide and for all phases of flight. These applications could potentially be expanded to provide guidance for ground movement operations.
Requirements for navigation applications on specific routes or within a specific airspace must be defined in a clear and concise manner. This is to ensure that the flight crew
Aircrew
Aircrew are the personnel who operate an aircraft while in flight. The composition of the crew depends on the type of aircraft as well as the purpose of the flight.-Civilian:*Aviator** Pilot-in-command** First officer** Second officer** Third officer...
and the air traffic controller
Air traffic controller
Air traffic controllers are the people who expedite and maintain a safe and orderly flow of air traffic in the global air traffic control system. The position of the air traffic controller is one that requires highly specialized skills...
s are aware of the on-board RNAV system capabilities in order to determine if the performance of the RNAV system is appropriate for the specific airspace requirements.
RNAV systems evolved in a manner similar to conventional ground-based routes and procedures. A specific RNAV system was identified and its performance was evaluated through a combination of analysis and flight test
Flight test
Flight test is a branch of aeronautical engineering that develops and gathers data during flight of an aircraft and then analyzes the data to evaluate the flight characteristics of the aircraft and validate its design, including safety aspects...
ing. For land-based operations, the initial systems used very high frequency omnidirectional radio range
VHF omnidirectional range
VOR, 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...
(VOR) and distance measuring equipment
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....
(DME) for estimating position; for oceanic operations, inertial navigation system
Inertial navigation system
An 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...
s (INS) were employed. Airspace and obstacle clearance
Minimum obstacle clearance altitude
Minimum Obstacle Clearance Altitude, or MOCA, is the lowest published altitude in effect between fixes on VOR airways, off-airway routes, or route segments that meets obstacle clearance requirements for the entire route segment. Within the United States, this altitude also assures acceptable...
criteria were developed based on the performance of available equipment, and specifications for requirements were based on available capabilities. Such prescriptive requirements resulted in delays to the introduction of new RNAV system capabilities and higher costs for maintaining appropriate certification. To avoid such prescriptive specifications of requirements, an alternative method for defining equipment requirements has been introduced. This enables the specification of performance requirements, independent of available equipment capabilities, and is termed performance-based navigation
Performance Based Navigation
ICAO performance-based navigation 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...
(PBN). Thus, RNAV is now one of the navigation techniques of PBN; currently the only other is required navigation performance
Required 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).
RNAV and RNP systems are fundamentally similar. The key difference between them is the requirement for on-board performance monitoring and alerting. A navigation specification that includes a requirement for on-board navigation performance monitoring and alerting is referred to as an RNP specification. One not having such requirements is referred to as an RNAV specification. An area navigation system capable of achieving the performance requirement of an RNP specification is referred to as an RNP system.
As a result of decisions made in the industry in the 1990s, most modern RNAV systems provide on-board performance monitoring and alerting, therefore the navigation specifications developed for use by these systems can be designated as RNP.
Many RNAV systems, while offering very high accuracy and possessing many of the functions provided by RNP systems, are not able to provide assurance
Systems assurance
Systems assurance is the planned and systematic set of activities that assure systems engineering processes and products conform with systems requirements for safety, reliability, availability, maintainability, standards, procedures, and regulations....
of their performance. Recognising this, and to avoid operators incurring unnecessary expense, where the airspace requirement does not necessitate the use of an RNP system, many new as well as existing navigation requirements will continue to specify RNAV rather than RNP systems. It is therefore expected that RNAV and RNP operations will co-exist for many years.
However, RNP systems provide improvements in the integrity of operation, permitting possibly closer route spacing, and can provide sufficient integrity to allow only the RNP systems to be use for navigation in a specific airspace. The use of RNP systems may therefore offer significant safety, operational and efficiency benefits. While RNAV and RNP applications will co-exist for a number of years, it is expected that there will be a gradual transition to RNP applications as the proportion of aircraft equipped with RNP systems increases and the cost of transition reduces.
Functional requirements
RNAV specifications include requirements for certain navigation functions. These functional requirements include:- continuous indication of aircraft position relative to track to be displayed to the pilot flying on a navigation display situated in his primary field of viewField of viewThe field of view is the extent of the observable world that is seen at any given moment....
; - display of distanceDistance Measuring EquipmentDistance measuring equipment is a transponder-based radio navigation technology that measures distance by timing the propagation delay of VHF or UHF radio signals....
and bearingBearing (navigation)In marine navigation, a bearing is the direction one object is from another object, usually, the direction of an object from one's own vessel. In aircraft navigation, a bearing is the actual compass direction of the forward course of the aircraft...
to the active (To) waypointWaypointA 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...
; - display of ground speedGround speedGround speed is the speed of an aircraft relative to the ground. Information displayed to passengers through the entertainment system often gives the aircraft groundspeed rather than airspeed....
or time to the active (To) waypoint; - navigation data storageNavigational databaseA navigational database is a type of database characterized by the fact that objects in it are found primarily by following references from other objects...
function; and - appropriate failure indication of the RNAV system including its sensors.
Lateral navigation
The inability to achieve the required lateral navigationLNAV
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...
accuracy may be due to navigation errors related to aircraft tracking and positioning. The three main errors are path definition error (PDE), flight technical error (FTE) and navigation system error (NSE). The distribution of these errors is assumed to be independent, zero-mean
Mean
In statistics, mean has two related meanings:* the arithmetic mean .* the expected value of a random variable, which is also called the population mean....
and Gaussian. Therefore, the distribution of total system error (TSE) is also Gaussian with a standard deviation
Standard deviation
Standard deviation is a widely used measure of variability or diversity used in statistics and probability theory. It shows how much variation or "dispersion" there is from the average...
equal to the root sum square
Sum of squares
The partition of sums of squares is a concept that permeates much of inferential statistics and descriptive statistics. More properly, it is the partitioning of sums of squared deviations or errors. Mathematically, the sum of squared deviations is an unscaled, or unadjusted measure of dispersion...
(RSS) of the standard deviations of these three errors.
PDE occurs when the path defined in the RNAV system does not correspond to the desired path, i.e. the path expected to be flown over the ground. Use of an RNAV system for navigation presupposes that a defined path representing the intended track is loaded into the navigation database. A consistent, repeatable path cannot be defined for a turn that allows for a fly-by turn at a waypoint (because nearness to waypoint and wind vector
Wind triangle
The wind triangle is a graphical representation of the relationship between aircraft motion and wind. It is used extensively in dead reckoning navigation.The wind triangle is a vector diagram, with three vectors....
may not be repeatable), requires a fly-over of a waypoint (because wind vector may not be repeatable), or occurs when the aircraft reaches a target altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
(because target altitude is dependent on engine thrust
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
and aircraft weight). In these cases, the navigation database contains a point-to-point desired flight path, but cannot account for the RNAV system defining a fly-by or fly-over path and performing a manoeuvre. A meaningful PDE and FTE cannot be established without a defining path, resulting in variability in the turn. Also, a deterministic, repeatable path cannot be defined for paths based on heading and the resulting path variability is accommodated in the route design.
FTE relates to the air crew or autopilot
Autopilot
An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being. An autopilot can refer specifically to aircraft, self-steering gear for boats, or auto guidance of space craft and missiles...
's ability to follow the defined path or track, including any display error (e.g. course deviation indicator
Course deviation indicator
Course Deviation Indicator is an avionics instrument used in aircraft navigation to determine an aircraft's lateral position in relation to a track. If the location of the aircraft is to the left of course, the needle deflects to the right, and vice versa.-Use:The instrument shows the direction...
(CDI) centring error). FTE can be monitored by the autopilot or air crew procedures and the extent to which these procedures need to be supported by other means depends, for example, on the phase of flight (i.e. take-off
Takeoff
Takeoff is the phase of flight in which an aerospace vehicle goes from the ground to flying in the air.For horizontal takeoff aircraft this usually involves starting with a transition from moving along the ground on a runway. For balloons, helicopters and some specialized fixed-wing aircraft , no...
, climb
Climb
thumb|right|An [[Embraer ERJ 145]] climbingIn aviation, the term climb refers both to the actual operation of increasing the altitude of an aircraft and to the logical phase of a typical flight following take-off and preceding the cruise, during which an increase in altitude to a predetermined...
, cruise
Cruise (flight)
Cruise is the level portion of aircraft travel where flight is most fuel efficient. It occurs between ascent and descent phases and is usually the majority of a journey. Technically, cruising consists of heading changes only at a constant airspeed and altitude...
, descent
Descent (aircraft)
A descent during air travel is any portion where an aircraft decreases altitude, and is the opposite of an ascent or climb. Descents are an essential component of an approach to landing...
, landing
Landing
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...
) and the type of operations. Such monitoring support could be provided by a map display.
NSE refers to the difference between the aircraft's estimated position and actual position.
Longitudinal navigation
Longitudinal performance implies navigation against a position along a track (e.g. 4-D control). However, at the present time, there are no navigation specifications requiring 4-D control, and there is no FTE in the longitudinal dimension. The current navigation specifications define requirements for along-track accuracy, which includes NSE and PDE. PDE is considered negligible. The along-track accuracy affects position reporting (e.g. "10 NM to ABC") and procedure design (e.g. minimum segment altitudes where the aircraft can begin descent once crossing a fix).Designation
An RNAV specification is designated as RNAV X, e.g. RNAV 1. The expression 'X' (where stated) refers to the lateral navigation accuracy in nautical miles, which is expected to be achieved at least 95% of the flight time by the population of aircraft operating within the airspace, route or procedure.There are no RNAV approach specifications.
Flight planning
Manual or automated notification of an aircraft's qualification to operate along an air traffic services (ATS) route, on a procedure or in an airspace is provided to ATC via the flight plan.External links
- RNAV Tutorial - Florida International University
- Getting To Grips with Modern Navigation - Airbus
See also
- VNAVVNAVIn aviation, Vertical NAVigation is an autopilot function which directs the vertical movement of an aircraft while cruising and/or on approach to landing....
- LNAVLNAVLateral 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...
- LPVLocalizer Performance with Vertical guidanceLocalizer performance with vertical guidance are the highest precision GPS aviation instrument approach procedures currently available without specialized aircrew training requirements, such as required navigation performance...