AIRSPACE

Navigational Reference System

In place since 2005, this extensive and underused waypoint grid above FL180 already provides direct routing using only 5-character waypoint names throughout the United States.

By Shawn Pruchnicki
ATP. Bombardier CRJ200


A significant component of NextGen, designed as a precursor to datalink communications, the NRS waypoint grid provides more navigational options for pilots and controllers alike.

FAA’s Next Generation Air Transport System (NextGen) is a multifaceted approach to developing a widespread performance-based navigational infrastructure.

This program is aimed at creating more direct routing, better management of traffic saturation situations and adding approaches and procedures where there currently are none.

The foundation of the program focuses on trajectory-based operations and ends the historical reliance on ground-based navigational aids. Many components of NextGen are already in place and being used by operators of all aircraft types and capabilities.

In fact, these operators are already realizing both a time and cost savings by using those NextGen components already in place and operational. Looking forward, NextGen uses various programs and concepts to achieve its goals—one of the most creative is the Navigational Reference System (NRS).

Grid creation and design

For many years it was clear to the industry that current airspace design was inefficient due to the seemingly random scattering of limited-range ground-based navigation sites. (See upper map, p 103.) As our navigation infrastructure has evolved over decades and air traffic has increased, the navigational infrastructure has continued to develop and expand as well.

In addition, the Joint Program & Devt Office (JPDO) and FAA predicted a 2 to 3-fold increase in air traffic in the US by 2025 from 2003 levels. NextGen is designed to help manage and improve the current inefficient airspace design, underused aircraft-based RNAV technology and the predicted increase in air traffic.

Several years ago, as part of the effort to correct this imbalance between airspace design and aircraft capability, FAA created the High Altitude Redesign (HAR) program to examine issues in the high altitude structure (18,000 ft and above). The agency recognized that, one day, datalink would be the key to more precise routing because controllers would be able to transmit lat/long coordinates to participating aircraft electronically.

Also, pilots would be able to accept this routing without entering all the required numbers manually. Realizing the cumbersome nature of trying to control traffic using this system now, FAA understood that it needed a system in the meantime that offered pinpoint navigational ability but yet a shorter easier waypoint system until datalink becomes a reality for the nation’s airspace operators.

Current distribution of high-altitude VORs in the US by ARTCC region.

Since we are years away from the reality of datalink being operational, it was decided that an interim solution was needed.

Members of the HAR group, which included representatives of both industry and FAA, provided numerous contributions to the NAS high altitude redesign. Among their numerous recommendations was the development of NRS to achieve this operational capability prior to the development of datalink.

The HAR group recognized the need for the creation of RNAV waypoints that were not linked directly to traditional ground-based navigation systems such as VORs. What they sought was a system that would provide precise point-to-point navigation, like traditional lat/long navigation but without the error-prone nomenclature.

Simply trying to use longitude and latitude would be too cumbersome and would raise the error rate associated with voice communication and data entry. What they designed was a gridlike system of RNAV waypoints that now blankets the US. (See map below.)

When first introduced and tested, the waypoints were only deployed in certain areas of the country in just a few ARTCCs. Shortly after this familiarization period, they were deployed in all 20 ARTCCs across the US. The hope was that the NRS waypoint system would allow increased flexibility, both in a strategic sense for flight planning and tactically as a rerouting tool.

Hannigan (2009) summarized the following expected benefits of NRS waypoints:

• Facilitate user-preferred routing based on satellite navigation

• Reduce pilot and ATC workload regarding communication and chance for error

• Be a tactical aid to resolve traffic conflicts

• Be a tactical aid in weather avoidance that may provide closer routing to original flightpath

• Satisfy processing requirements for filing at least 1 fix per ARTCC

Current distribution of 1600 NRS waypoints and US ARTCC regions.

To achieve these benefits, it was originally decided that the waypoints would be spaced every 30 minutes of latitude and every 2 degrees of longitude, providing a total density of approximately 1600 waypoints across the US (See diagram, p 104.)

It was felt that this initial density was sufficient to offer the stated advantages without initially saturating the airspace with thousands of waypoints. If the concept proved successful and additional waypoints were needed, their density could be increased.

These initial 1600 waypoints added a significant number of fixes for navigation which was most noticeable in the western US, where ground-based navigational aids are sparse. Despite the utility and success of the program, NRS waypoints are rarely used east of the Mississippi due to the extreme density of pre-existing navaids and the high traffic flow up and down the eastern seaboard.

These factors have created an environment where preferred and fixed routes are the primary source of controlling traffic flow. Direct routing in this area of the country during the day is very rare. Since the NRS’s inception in 2005, not every NRS waypoint created has been filed in flightplans throughout the NAS.

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