RNAV

Background

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). RNP systems add on-board performance monitoring and alerting to the navigation capabilities of RNAV. As a result of decisions made in the industry in the 1990s, most modern systems are RNP.