Photo: courtesy of FAA

The Federal Aviation Administration's Required Navigation Performance program is establishing performance standards for U.S. airspace that will allow aircraft to take advantage of installed on-board technology and break from the traditional (and somewhat rigid) ground-based navigation system. With this transition to performance-based navigation, aircraft will be able to fly flexible, point-to-point routes reliably and accurately. This leads to reduced fuel burn and higher levels of safety. Conventional navigation methods will be supported in U.S. airspace for many years to come, however, so a mixed-equipage environment is presenting challenges now and into the future.

For decades, modern aviation has relied on ground-based navigation aids (NAVAIDS), such as mountain top VHF omni-ranging transmitters, to guide aircraft flying in the United States and abroad. Low-altitude routes for lower performance aircraft and high-altitude routes for jets were designed and published based on the location of these NAVAIDS. While providing stable and predictable paths, routes based on ground-based NAVAIDS (called Victor Airways and Jet Routes) lack flexibility and often lead to inefficient, circuitous routing through fixed "highways in the sky." In addition, the location and capacity of these conventional routes are constrained by the performance of NAVAIDS.

With MITRE support and guidance, the Federal Aviation Administration's (FAA) Required Navigation Performance (RNP) program has recently developed a Roadmap to leverage new navigation technology and adopt new performance-based navigation standards. With RNP, the FAA will improve airspace use and implement new procedures by taking advantage of point-to-point "area navigation" (RNAV) and the improved navigation performance achieved by the Global Positioning System (GPS), now fitted on many modern aircraft. This will allow aircraft to fly more direct paths and eliminate the need for equipped aircraft to be anchored to ground-based NAVAIDS.

"Today, manufacturers Boeing and Airbus are fitting their aircraft with very advanced flight management systems, navigation data bases, and navigation sensor technologies. Under RNP, aircraft will be able to take advantage of these on-board systems in a more proactive way and move to a performance-based system," explains Dr. Hassan Shahidi, MITRE's RNP program manager. "The majority of aircraft operating in certain airspace, for example at high altitudes and at some of the busiest airports, have the tools and the capabilities on-board to fly point-to-point (RNAV). And, those that currently aren't outfitted with the necessary equipment will have the incentive to install these systems in the future so they can also navigate in an un-tethered fashion. This will translate into reduced route lengths and fuel consumption without compromising safety. And, improved efficiency and capacity means more affordable air services for consumers and providers."

Photo: courtesy of FAA

Development and Implementation

In its final form, RNP will be a comprehensive set of navigation and safety standards applied to all phases of a flight, including departure, en route, arrival, and final approach operations. MITRE's Center for Advanced Aviation System Development (CAASD) is playing a significant role in the development and implementation of the RNP concept as well as RNP procedures, costs, risks, and benefits. One of MITRE's key roles with this initiative is the modeling and simulation of each of the phases of an RNP-enabled national airspace. To assist the FAA in defining new procedures and assessing the effects of mixed equipage, MITRE uses route definition and flyability simulations to visualize what might happen for a variety of procedure options. With a constant focus on safety, MITRE's analyses include modeling the effect of more optimal aircraft-to-aircraft separation (e.g., from the current eight- to 10-mile lateral separations.) MITRE also uses airspace performance models to analyze the effect of partial and complete conversion of the aviation fleet to RNP and the associated new routes tailored to airspace and operational needs.

"While it may take five to 10 years before we see reduced separation minima—perhaps much longer for the mixed-equipage environments—the modeling and simulation work we're doing now will help to implement RNAV and RNP procedures for more efficient operations in the near term where needed," notes Shahidi. For example, Shahidi's team is designing the RNP Parallel Approach Transition (RPAT) concept that will enable more arrivals into airports with parallel runways during reduced weather conditions.

To quickly and affordably move to RNP, the avionics industry is producing new performance-based navigation equipment and modifying software for existing navigation equipment, tailored to specific aircraft and aviation needs. "By relying on the avionics industry to develop the equipment needed for RNP, the government can focus on safety, certification, operational standards, interoperability, and procedures while the aviation industry can focus on equipage and training," says Shahidi. "The FAA is setting performance standards, and it is up to industry to develop products that meet those standards." Also, as avionics vendors compete for business, development and maintenance costs can be reduced.

To facilitate a quick yet responsible phase-in of RNP operations and to aid in equipment certification, MITRE is assisting the FAA in building an inventory of existing and upcoming aircraft equipment capabilities. MITRE is also helping the FAA to leverage existing equipment and assess new equipment designs against performance goals and safety measures. MITRE has been leading an FAA and industry collaborative effort to identify RNP implementation priorities, key sites, and schedules, recently contributing to the establishment of the FAA's Roadmap for Performance-based Navigation.

Not Just for the Future

To test key concepts for RNP, MITRE recently designed a new RNAV Departure Procedure for Dulles Airport near Washington, D.C., incorporating procedure design criteria and performance requirements to allow independent parallel departures during marginal weather conditions. These new runway procedures and their attendant equipment will increase departure capacity at Dulles from approximately 52 aircraft per hour to 78 aircraft per hour during these marginal conditions, resulting in potential savings of $5 million per year for just one of the major Dulles hub airlines.

MITRE continues to enhance the visualization and simulation tool for terminal procedure design, recently codifying a repeatable process to design, test, and publicly chart terminal RNAV and RNP procedures successfully and rapidly. Several of these advanced procedures have already begun providing operational benefits in terminal areas around the country. MITRE is also helping in the redesign of the high-altitude airspace structure using RNAV and RNP concepts. FAA studies show that this redesign will result in significant operational cost savings and improve the reliability of scheduled flight operations during poor weather conditions. The use of RNP airspace and procedures, coupled with increasing aircraft fleet usage of GPS and other navigation systems, create the foundation for a satellite-based air traffic management system in the United States within the next decade.

—by Nadine Monaco

Page last updated: February 19, 2004 | Top of page