Area navigation

Area navigation (RNAV) 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 navigate directly to and from the beacons. This can conserve flight distance, reduce congestion, and allow flights into airports without beacons. Area navigation used to be called "random navigation", hence the acronym 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 RNAV routes in the contiguous United States due to findings that aircraft were using inertial navigation systems rather than the ground-based beacons, and so cost–benefit analysis was not in favour of maintaining the RNAV routes system. RNAV was reintroduced after the large-scale introduction of satellite navigation.

The continuing growth of aviation increases demands on airspace capacity, thus emphasising 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 controllers 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 testing. 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 systems (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).

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