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2. Area Navigation Definitions

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Area Navigation Definitions

NOTE: Because definitions may differ between international organisations, the following definitions have been chosen for this publication.

The degree of conformance between the estimated, measured or desired position and/or the velocity of a platform at a given time and its true position or velocity. Navigation performance accuracy is usually presented as a statistical measure of system error and is specified as predictable, repeatable and relative.

Actual Navigation Performance (ANP)
A measure of the current estimated navigation performance, excluding Flight Technical Error (FTE). ANP is measured in terms of accuracy and integrity and may be affected by the type and availability of navigation signals and equipment.

Area Navigation (RNAV)
A method of navigation which permits aircraft operation on any desired flight path within the coverage of station-referenced navigation aids or within the limits of the capability of self-contained aids or a combination of these.

An acronym (aeronautical information regulation and control) signifying a system aimed at advance notification based on common effective dates, of circumstances that necessitate significant changes in operating practices.

Aeronautical Radio Incorporated standard document for coding routes for application in RNAV systems.

An indication of the ability of a system to provide usable service within the specified coverage area, defined as the portion of the time during which the system is to be used for navigation during which reliable navigation information is presented to the crew, autopilot, or other system managing the flight of the aircraft.

Continuity of service
The capability of the total system (comprising all elements necessary to maintain aircraft position within the defined airspace) to perform its function without non-scheduled interruptions during the intended operation.

Estimated Position Uncertainty (EPU)
A measure on a scale which conveys the current position estimation performance. Also called Estimated Position Error (EPE).

Flight Technical Error
The accuracy with which the aircraft is controlled as measured by the indicated aircraft position with respect to the indicated command or desired position. It does not include blunder errors.

Geodetic System
A system to mathematically describe the shape of the earth’s surface

Global Navigation Satellite System (GNSS)
A world-wide position, velocity and time determination system that uses one ore more satellite constellations.

    NOTE: Currently, only the US Department of Defence has allowed civilian use of their system. In the future the Russian owned (military) GLONASS and the European (civil) Galileo (under development) systems could be part of GNSS.

Global Positioning System (GPS)
The ‘NAVSTAR’ satellite system owned by the US Department of Defence. It is a satellite based radio navigation system composed of space, control and user segments. The space segment consists of satellites, the control segment of monitor stations, ground antennas and a master station. The user segment consists of antennas and receiver processors that derive time and compute a position and velocity from the data transmitter from the satellites.

The ability of a system to provide timely warnings to users when it should not be used for navigation.

Primary means of navigation
A means of navigation which satisfies the necessary levels of accuracy and integrity for a particular area, route, procedure or operation. Failure may result in, or require reversion to an other means of navigation or RNP level.

The measured range to a satellite without correction for small inaccuracies in time (clockbias).

RAIM (Receiver Autonomous Integrity Monitoring)
A technique whereby a GPS receiver determines the integrity of the GPS navigation signals using only GPS signals or GPS signals augmented with altitude. This determination is achieved by a consistency check among redundant pseudorange measurements. At least one satellite in addition to those required for navigation must be in view for the receiver to perform the RAIM.

Required Navigation Performance (RNP)
A statement of the navigation performance necessary for operation within a defined airspace.

    NOTE: Navigation performance and requirements are defined for a particular RNP type and/or application.

A unit capable of providing information for use by the RNAV or FMS.

Sole means of navigation
Use of RNAV system without the capability to monitor or fall back to a second navigation system. Also known as ‘stand alone’.

Supplementary means of navigation
A means of navigation which satisfies one or more of the necessary levels of accuracy, integrity or availability for a particular area, route, procedure or operation. Failure may result in, or require reversion to, another means of navigation.

Vertical Navigation (VNAV)
A method of navigation which permits aircraft operation on a vertical profile using altimetry sources, external flight path references, or a combination of these.

A specific geographical location used to define an area navigation route or flight path of an aircraft employing area navigation. Waypoints are defined as either:

  • Fly-by
  • Fly By
    A waypoint which requires turn anticipation to allow tangential interception of the next segment of a route or procedure, or

  • Fly-over
  • Fly Over
    A waypoint at which a turn is initiated in order to join the next segment of a route or procedure.

WGS-84 (World Geodetic System 1984).
The standard geodetic reference system for future navigation with respect to international civil aviation. (Required for RNAV operations.)

Source: FCRG

See also:
History of RNAV
Area Navigation Definitions
RNAV System Description
Required Navigation Performance (RNP)
RNAV Development
RNAV System Limitations
Global Positioning System (GPS)

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