Navigating toward NextGen by taking NAS into the future
Going from existing ATC and flight planning into ADS–B and simpler flying.
By Michael Hannigan
Air Traffic Manager, FAA
As traffic management standards evolve toward those of NextGen, it is critical to work under the constraints of the system without affecting daily operations.
Today's National Airspace System (NAS) is the product of half a century's work, built on the technologies of the mid-20th century and modified constantly to meet the burden of the present. We use radars that were invented in the 1930s to see and VORs invented in the 1960s to find our way, but today new tools are being developed, such as ADS-B, and new tools exist, such as GPS/RNAV, that can catapult our way toward a safer and more efficient air navigation system.
Thinking efficiently and using what is available in our aviation environs, we can change navigation in the NAS safely and radically—and we can do so, not tomorrow, but today.
Land-based navigational aids are the structure on which the NAS is built. Users today are assisted by GPS, but only to gain individual efficiencies in the NAS and not as a larger NAS or universal efficiency.
The problem is how we prepare for the future and institute improvement today, while delivering change to the customer without too much pain. How we determine and install the foundation to NextGen is the critical step to future success. This foundation must be instituted to pave the road for the smooth transition of the many NextGen concepts.
The solution is to modernize the use of airspace with technologies that are available today. Using existing functionality will afford support for today's problems while simultaneously preparing us for the future. The creation and use of robust RNAV networks using the Navigational Reference System (NRS) can bridge what we currently see as terminal and enroute domains and help us deliver the Flintstones to the Jetsons, so to speak.
There was a time when we spoke of the concepts of "Free Flight" and the ability of aircraft to fly safely and efficiently on their own performance standards. Using the NRS grid to build routing only where traffic management requires takes us steps closer to these concepts and prepares us for the future traffic management standards of NextGen.
What exists today
More than 90% of aircraft flying above FL180 can navigate using RNAV. We no longer need to rely on ground-based navigation to travel in these altitudes and with RNAV we only need structured routing where structure is needed. This technology is the foundation of everything NextGen promises and we can complement the acceleration of change if we use what is available to aviation at this moment.
Critical to this acceleration is to work under the constraints of the system without making an impact on our daily operations. The NRS is one such tool ready to be used. This sparse grid of 1600 published navigational fixes was originally planned to be published with 6000-plus fixes. These published waypoints appear every 30 minutes of latitude and every 2 degrees of longitude and are the result of studies and scientific development from FAA's High Altitude Redesign (HAR) program.
Today there is a gradually increasing use of these fixes, but with a small amount of effort we can dramatically increase their use in the NAS.
A change to the definition of federal airways in the Federal Air Regulations made the implementation of RNAV routing a reality. The change permitted an airway to begin or end at a waypoint instead of at a navigational aid (navaid). This change enabled the HAR program to rely on RNAV for route design instead of navaids or other ground-based navigation. Originally, the RNAV routing was to be limited to those aircraft that used satellite-based (GPS) navigation.
This was later changed to include aircraft that used DME/DME/ IRU equipment to increase the number of aircraft eligible to use the routes high enough to make operations efficient. The inclusion of aircraft with DME/DME/IRU equipment led to restrictions to the RNAV routes in the form of MEAs, due to the location of terrain and the limitation of navaids in the same area.
NRS fixes or "K-fixes" have been used successfully to navigate in the middle of the country where there is limited land-based navigation. They have been used more recently by the command center in the transition of "playbooks" to RNAV routing. NRS fixes are used today with the "wind route playbooks" that replaced the "chokepoint playbooks." These fixes have also proved handy in an environment where 5-letter fix names have become less available and more phonetically cumbersome.
RNAV routing in the flight levels has been very successful in the development of Q-routes on the US west coast, across the Gulf of Mexico and—in the past 2 years—as a departure route (Q42) from New York/New Jersey airspace. The benefits of this routing have been well documented and the NRS offers a blank slate in the flight levels for expeditious transformation. This potential for change can be accomplished even as we transition the enroute system to ERAM automation, install ADS-B and train a new generation of air traffic controllers.
Air Traffic System Command Center's (ATSCC) new wind route options playbook uses RNAV routing and offers system users efficient options. Entry to routes is determined by forecast winds.
Historically, the way the NAS delivers aircraft has been very successful, but this is not ideal for the performance-based system of NextGen. When looked at as a clean sheet design paper, the new system does connect well with the promises it holds and the system on which it is being built. But, without a solid foundation, the first rising tide will wash the benefits away.
Ground-based equipment has seen an incredible increase in navigational assistance with the growth of terminal RNAV routing. Although much of this has been built overlying conventional terminal routings, it has provided much needed benefits for the customer. In the enroute environment, the advent of RNAV routing (Q-routes) has seen routing efficiencies around areas not available for efficient navigation.
The routings on the US west coast have reduced time to climb to requested altitudes and flight mileage, especially around military airspace. They have also provided air traffic services with increased flexibility in managing traffic. The routes across the Gulf of Mexico have shortened flight times and reduced constraints previously experienced with land-based navigation. And the northern routes are used occasionally in severe weather events, allowing for structured escapes around the problem areas.
Another opportunity exists with enroute RNAV routing. It allows efficient delivery of aircraft in order to use optimum profile descents (OPDs) and optimum profile ascents (OPAs). OPAs and OPDs would be the umbrella term for some concepts already being used—CDAs and tailored arrivals. These concepts move us toward having the ability to configure aircraft to perform most efficiently, and creating enroute structure allows the aircraft to fully realize its performance.
Critical to today's environment, with its fluctuating (or increasing) fuel prices, is making airspace and routing work for these concepts. We can no longer allow fuel-laden aircraft to depart and level off many times in order to fit in the system when we can build routing to allow smooth transitions.