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.
One-letter identifiers for ARTCCs.
However, flightplan data analysis shows NRS waypoint usage has occurred in all 20 ARTCCs. Although usage is uncommon in the eastern US, waypoints in the Midwest show the highest level of usage.
Many operators consider the current waypoint density sufficient, but if more fixes are needed the system is designed to expand by increasing waypoint density so that they will be spaced every 10 minutes of latitude and every 1 degree of longitude. This increase will produce a total of approximately 6600 NRS waypoints.
When the NRS was first designed, its architects realized they would need to create a waypoint naming system that had to meet numerous objectives to be successful (Boetig & Timmerman, 2003; Hannigan, 2009).
The criteria they developed to guide them in this process required that waypoint names:
• be easy to communicate
• have a low potential for error
• be consistent with principles that guide names for navigational fixes
• be intuitive as to the general location of the fix (ie, provide “geographic awareness”)
• minimize impact to airborne equipment
• be usable by a majority of current aircraft
• incur only minimal changes (eg, database only) to ground automation
• support implementation across the US
• be easier to use than fixes delineated by full latitude and longitude coordinates
With the historical standard of RNAV waypoint names being 5 characters long, it was decided to maintain this philosophy for the new system. The challenge was to essentially compress all the specific data that traditional lat/long coordinates provide in just 5 characters.
NRS waypoint grid structure and nomenclature.
This challenge was even greater if one considers that, when first developed, it was believed that the NRS grid system might expand outside the continental US.
As such, per ICAO standards, the first letter in the waypoint name was to signify that this waypoint was in the US FIR and, as such, would be required to start with the letter K.
With a goal of creating some level of geographical awareness by simply looking at the waypoint name, the 2nd character was used to represent the ARTCC area in which the waypoint is located. However, since ARTCC abbreviations are 3 letters long, they created a list of single letters to identify a particular ARTCC.
The table above lists centers and codes currently in use in NRS nomenclature. The last 3 characters of the 5 signify the latitude and longitude of the waypoint on the NRS grid. (See diagram below for an example of a NRS waypoint.)
These waypoints can be entered into most navigation databases like any other RNAV waypoint. Just as precise as traditional lat/long navigation, a waypoint such as KD54U tells us that it is located in the US, is in Denver ARTCC airspace and can be found by going to latitude 54 and longitude U on a high altitude chart.
This is the same point in space as N39.00 W106.00 but much easier to communicate and less error-prone on a busy ATC frequency.
Adding NRS waypoints to the NAS has offered numerous advantages to strategic flight planning by offering more direct routing options. Flights around special use airspace, TFRs, MOAs and the like can be much easier to accomplish using these waypoints.
However, with the current floor of these points being 18,000 ft, not every aircraft type will be able to take advantage of them. When flight planning, consultation of a high altitude enroute chart or most flight planning software programs will show which NRS waypoints are available between departure and destination airports.
A pilot no longer has to only consider VORs and the randomly distributed RNAV waypoints in the NAS—the NRS waypoint grid offers many other flightplan filing options. In fact, some operators simply look at a chart (or flight planning software) and create their route by filing NRS waypoints that lie on a straight line between departure and destination airports.
In addition, the proliferation of these points makes achieving the FAA requirement of filing 1 waypoint per ARTCC sector easy to accomplish. (The chart above shows NRS waypoints on a high-altitude chart.)
NRS waypoints offer a significant navigational option for flightcrews and planners alike, but air traffic controllers can also use these waypoints to manage traffic flows better during times of saturation and airspace closure.
Individual air traffic controllers have these waypoints in their airspace at their disposal. In addition, the Air Traffic Control System Command Center (ATCSCC) uses a number of preplanned routes across the country in the event that traffic flow diversions are needed due to weather or equipage outages.