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Perspectives: RNP: Foundation for ATM Efficiency

By Amr ElSawy and Dr. Hassan Shahidi | March 1, 2003
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In July 2002, the Federal Aviation Administration (FAA) announced its commitment to implementing required navigation performance (RNP) airspace and procedures throughout the U.S. National Airspace System (NAS). It is an important step to improve airspace capacity and efficiency. FAA also included RNP in its Operational Evolution Plan for near-term system enhancements.

FAA and users have placed an increased emphasis on RNP implementation by establishing a dedicated RNP program office and a collaborative, government/industry Terminal Area Operations Advisory Rulemaking Committee (TAOARC). The program office will draw upon disciplines across FAA for standards, certification, procedures and airspace design relating to the implementation of RNP. The TAOARC is developing strategy and rulemaking proposals for near-term improvements and maturation of longer-term RNP concepts. For harmonization, FAA is coordinating decisions internationally and participating in Eurocontrol’s task force, developing terminal airspace procedures and policy.

Around a number of years, RNP is the conversion of navigation procedures, airspace, route structures and separation standards to a technology-independent structure. It is not tied to the use of a specific system or avionics. The performance specifications are the standard. Airspace and procedures will be based on an RNP level, such as RNP 2.0 envisioned for en route and terminal operations, starting in 2004. Aircraft equipped for an RNP 2.0 route, and with crews trained and approved to use it, can fly any RNP 2.0 procedures or in any RNP 2.0 airspace.

RNP procedures offer a more accurate and predictable flight path in all phases of flight. Separation buffers used for safety between routes or between aircraft and terrain obstacles will be redesigned to account for RNP’s improved accuracy and predictability. Many aircraft equipped with flight management systems, enhanced area navigation (RNAV) capabilities, databases, and integrated or standalone sensors such as GPS will be RNP participants. Some will reap near-term benefits from RNP without additional avionics investments. Others will have to upgrade avionics for improved alerting or flight path definition, to participate in RNP.

This transition to RNP is not without challenges. There is enough variation in the navigation computers and databases installed in aircraft today to require special efforts to account for these differences, or limit their usage.

Initially, enhanced RNP 2.0 terminal procedures will overlay existing vector-based patterns and RNP 0.3 approaches will overlay existing ILS instrument procedures. Once aircraft performance is better understood and air traffic control automation is modernized to accommodate newly designed, flexible flight paths, RNP procedures will be designed anew. They will need to support mixed equipage since not all aircraft will be participating in RNP or will fly RNP 2.0 or RNP 0.3. For additional benefits, some procedures, referred to as SAARs (special aircraft and aircrew authorization required) will be developed for more advanced operators that will allow improved minimas or enable simultaneous arrivals and departures at certain locations.

Early experience will be gained and results combined with other research activities to accommodate a broad population of operators. One research activity launched recently is a survey of aircraft capabilities to facilitate the development of RNP-level options for avionics configurations existing today and planned five years out.

In support of RNP implementation, the Mitre Corp.’s Center for Advanced Aviation System Development (CAASD) is working collaboratively with FAA and industry. For example, Mitre CAASD helped design an RNAV departure for Washington Dulles Airport, enabling independent parallel departures during marginal weather conditions. During these conditions, this procedure will increase departure capacity by almost 50 percent, resulting in potential savings of $5 million per year for a major airline at Dulles.

RNP applies in all flight phases. We envision RNP 1.0 departures transitioning to RNP 1.0 en route operations, followed by RNP 1.0 arrivals and RNP 0.3 approaches (lower in some locations). RNP will allow flexibility in traffic flow (e.g., parallel offset, "passing lanes" and tailored holds) not achievable today.

RNP is critical to the establishment of a performance-based air traffic management system. Government and industry are developing a roadmap for RNP implementation, outlining the steps for the next 10 years. The use of RNP is the foundation for increasing overall system efficiency for decades to come.

Amr ElSawy is a senior vice president at the Mitre Corp. and general manager of Mitre CAASD. Dr. Hassan Shahidi is a program manager at CAASD and heads CAASD's RNP work program.

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