The figure below depicts the differences in the obstacles clearance areas for traditional, RNP and RNP AR (procedures that require special approval to fly) procedures. The result is a lower approach minimum because obstacles that were previously considered using the trapezoidal method are no longer a factor when using linear containment criteria specified for RNP.
For example, an approach with an RNP value of 0.3 means that the closest obstacle perpendicular to the course centerline must be no closer than 0.6 NM away. continued on page 2ΔΆ Required Navigation Performance from cover story In general terms, an approach with a specified RNP value means the perpendicular distance between the course centerline and the nearest obstacle must be at least 2X the RNP value specified for the approach. For the purpose of procedure design, RNP represents the navigation performance required to maintain flight within the obstacle evaluation area associated with the procedure.
RNP procedures rely solely on satellite based navigation (GPS) and, therefore, use linear obstacle evaluation areas for procedure design and determination of approach minimums. Whenever obstacles are observed to be within the obstacle clearance area, approach minimums must be raised to ensure clearance from these obstacles. Conventional procedure design predicated on ground-based navaids uses trapezoidal obstacle clearance areas which increase as a function of the distance from the navaid (navigation accuracy increased as the aircraft came closer to the facility). RNP procedures are considered 3-Dimensional as they provide longitudinal, lateral and vertical path deviation information. The benefits of RNP & RNP AR (Authorization Required) are derived directly from procedure design flexibility, the use of reduced obstacle clearance areas, and curved flight paths. The graphic below depicts the general benefits to RNAV and RNP over conventional airspace design, routes, and procedures. This capability enables operations with reduced obstacle clearance criteria for terminal area procedures as well as closer route spacing - a major contributor to the benefits of performance-based navigation. These systems also have the ability to navigate with a much higher degree of accuracy along with the ability for the flight crew to monitor the navigational performance of the system and alert the flight crew if a certain performance requirement is not met. RNP defines the navigation performance level required to operate in a particular airspace or on a designated route (i.e. RNP is the latest advancement in RNAV systems evolution. The performance requirements for these systems are defined in specific FAA Advisory Circulars and Technical Standards Orders. Most RNAV systems are capable of utilizing navigation signals from various ground and space based facilities to achieve a high level of position accuracy. RNAV systems and their associated operational procedures have been evolving for air transport, regional and corporate aircraft for many years. The strategy bases its foundation on two key navigation concepts: RNAV (Area Navigation) and RNP (Required Navigation Performance). Using this strategy, the FAA intends to address current limitations on air transportation capacity by making more efficient use of the airspace.
Performance-based navigation provides a basis for the design and implementation of non-conventional flight paths for airspace design and obstacle clearance. Performance based navigation is a general term that defines navigation performance requirements for an air traffic route, instrument procedure, or defined portion of airspace.
1 Direct-TO CURRENT HEADLINES HONEYWELL FMS QUARTERLY UPDATE AND NEWSLETTER JANUARY 2010 Technical Update FMS SIL Bendix/King Update GNS/XLS Qualified for P-RNAV Aircraft Database and SmartPerf Learning Pilot Training & Operational Support Data Loading Dos and Don ts Technical Ops Center FAQs Give Us Your Feedback Industry Update NextGen Taskforce Contact Us RNP Required Navigation Performance and AR In 2003, the FAA published THE ROADMAP TO PERFORMANCE-BASED NAVIGATION, which publicly announced the strategy to modernize the NAS (US National Airspace System).