Departing and arriving airline traffic at FLL (Intl, Fort Lauderdale FL). NextGen, due to be operational by 2025, will encompass commercial and general aviation, as well as military aviation (both manned and unmanned) and civilian space transportation.
A major overhaul is about to transform the National Airspace System (NAS). The result, which is scheduled to be fully operational by 2025, is called the Next Generation Air Transportation System—or NextGen—and it will profoundly change the way we navigate and how we fly.
Decisions that will create and define NextGen are being made right now, and many of the changes will be incorporated over time, so you won’t have to wait 15 years or more to see the result. Some of them are already happening now.
NextGen’s purpose is to create more capacity. Today the NAS handles more than 750 million passengers each year. Some forecasts say that could grow to 1 billion by 2015 and perhaps even triple by 2025. The current system simply won’t absorb that much growth.
Today, the US Joint Planning and Development Office (JPDO), in conjunction with the Departments of Transportation, Homeland Security, Defense, and Commerce—plus FAA, NASA and the White House Office of Science & Technology Policy—are creating and defining NextGen.
One objective is to combine the needs and requirements of commercial and general aviation, military operations (manned and unmanned) and commercial space transportation into an integrated system, using new technologies that will accommodate all the anticipated growth.
But what will NextGen look like? And how will it work? How will it affect flightcrews operating within the NAS?
Performance-based navigation
NextGen will shift most aeronautical navigation from ground-based navaids to GPS, both in the air and on the ground. Phasing-out of ground-based navaids will create a more “aircraft-centric” system.
Performance-based navigation will comprise 2 main components—area navigation (RNAV) and required navigation performance (RNP). SIDs, enroute navigation, STARs and approaches will be based on RNAV waypoints. This will allow more direct routing, reducing flight time, fuel consumption and greenhouse gas emissions.
Use of RNP will allow for creation of corridors between RNAV waypoints that will require a more precise path than today’s airways. Aircraft will be contained within a much narrower corridor of airspace. As many as 4 RNP corridors may exist in the same airspace defined by a single airway today, so creating more capacity where it is needed.
In addition, more precise approach procedures can be flown into airports, demanding greater precision. RNP Special Aircraft and Aircrew Authorization Required (SAAAR) approach procedures will allow access and lower approach minimums into airports surrounded by terrain or obstacles.
In high-density areas, RNP arrival procedures and SAAAR approaches will increase capacity through the use of curved and narrower segments defining the arrival/approach routes.
RNP has vastly improved safety and access into JNU (Juneau AK) by providing an accurate approach with lateral and vertical guidance through a narrow corridor flanked by mountainous terrain.
Inversely, the curved and narrower segments that will define future RNAV departure routes will allow more departure fixes to be built into the procedure and thus increase capacity of departing traffic.
ADS-B
Perhaps the most futuristic component of NextGen is Automatic Dependent Surveillance–Broadcast (ADS-B).
Briefly, ADS-B will shift aircraft position tracking away from less accurate ground-based radar to GPS. As with performance-based navigation, the ground-based system—radar—will be replaced by an “aircraft-centric” system.
Artist’s conception of NextGen components in the year 2025, including equivalent visual operations, ADS-B, air traffic flow management and trajectory-based ops.
The immediate benefit will be reduced separation requirements. Radar-based separation standards of a few miles will give way to GPS separation standards of a few hundred feet, allowing more aircraft to operate in a finite airspace.
ADS-B will incorporate 2 different satellite networks. GPS signals will define aircraft position to within a few feet. This information will then be transmitted from the aircraft, via the ADS-B transponder, to a network of satellites that will then broadcast the aircraft position, altitude, heading and horizontal and vertical speed to ATC facilities and other aircraft.
For the first time, pilots will be able to see real-time, radar-like displays that include the same information the controller sees. All flightcrews will be able to see all traffic in the area, on displays that will also show terrain topography, weather, and (when on the ground) airport diagrams.
Trajectory-based airspace and operations
NextGen will primarily use trajectory-based operations (TBO) to manage traffic. TBO considers the 4D picture of an aircraft’s present flightpath or proposed flightplan, then coordinates aircraft separation and flow management between the 4D trajectories (4DTs) of all other equipped aircraft.
An aircraft’s 4DT is the precise description of its path in space and time. This path is Earth-referenced (ie, specifying latitude and longitude), and contains current and projected altitudes and the times. Certain waypoints in the aircraft’s 4DT will be associated with controlled time of arrivals (CTAs)—time windows in which the aircraft can be expected to cross waypoints within a prescribed performance tolerance.
Advantages of performance-based area navigation over today’s ground-based system.
CTAs will be used to regulate traffic through congested airspace or meter traffic on airport runways and taxiways. Required TBO equipment will include a digital data communication system between ground facilities and aircraft, as well as from aircraft to aircraft. It will also require ground-based and airborne automation to create, exchange and execute 4DTs. The system will have to accommodate unforeseen and quickly changing events such as a rapid decompression/emergency descent maneuver or an incorrectly flown flightpath.
ANSP-managed and self-separation ops
NextGen will entail a transition from rules-based operations and separation (ATC-based standards) to more flexible performance-based operations and separation (trajectory-based standards). The controller will become the air navigation service provider (ANSP), primarily responsible for overall traffic flow.
At times the ANSP will be responsible for traffic separation. At other times he/she will delegate that responsibility to either the flightcrews or to separation-capable aircraft. Many aircraft will have the ability to perform airborne self-separation, spacing and merging tasks while navigating and executing 4DTs precisely. ATC will then be able to focus on overall flow management instead of individual flight management.
Flow corridors
4DT will allow large numbers of separation-capable aircraft to travel within “flow corridors” during high-demand operations in congested airspace. In airspace where traffic is moving in roughly the same direction with near-parallel trajectories, such as arrivals into a major airport, the ANSP will implement flow corridor procedures. Traffic will be routed through “tubes” or “bundles” that will allow a high volume to move through a finite airspace. In addition, the course of the flow corridors could be shifted to avoid weather, accommodate additional traffic or circumnavigate restricted airspace.
Super-density terminal ops
Typical flow corridor used during high-demand operations in congested airspace.
Currently, NAS is based on a “first come, first served” philosophy. Under NextGen, it may become necessary to change gradually into a system of “best equipped, best served.” Under this scenario, during high-demand periods, super-density arrival and departure terminal operations will be implemented at major airports to increase runway throughput. Aircraft equipped with the highest level of automation will be sequenced on approach, on departure and while on the surface to maximize the number of aircraft using available airspace.
Super-density arrival/departure terminal operations will increase runway throughput at major airports.
Super-density operations will include real-time wake vortex separation considerations as well as environmentally friendly low-power/low-noise approaches. The use of super-density corridors will allow highly automated aircraft to use certain runways, while aircraft with lower levels of automation would either be sequenced into parallel runways or other airports. During periods of low demand, the system would scale down and allow operations for all aircraft regardless of automation levels.
Equivalent visual operations
Technical advances in avionics displays (EFVS and SVS), combined with the accuracy of GPS, the predictability of TBO and the situational awareness of ADS-B will enable NextGen aircraft to operate without relying on direct visual reference to one another.
Aircraft will also be able to conduct ground, departure and arrival operations without regard for reduced visibility. ANSPs will be able to manage traffic in all visibility conditions, resulting in more predictable and efficient operations.
Surface operations
NextGen’s impact on airport surface operations will enhance the capabilities of existing infrastructure. It will also permit new infrastructure development as needed, at GA airports as well as major hubs.
Improved surveillance, automation and information-sharing will enhance surface and tower operations. Surface ops will move from a highly visual, tactical environment controlled by an ATC tower, to a more strategic set of flow-controlled ops independent of visibility and less dependent on tower control.
Aircraft operations will change to a long-term, gate-to-gate, strategic flow. TBO, metering, controlled time of arrival exchange and more flight-specific time adjustments will all help improve ground operating efficiency of pushback, taxi, runway crossing, deicing and ground support ops.
NextGen network-enabled weather (NNEW) system will provide a real-time, easy-to-interpret weather picture accessible to all decisionmakers involved in flight planning, execution or flow control.
Trajectory-based procedures may also be used at high-density airports to expedite taxiing traffic and schedule active runway crossings.
Equivalent visual ops-equipped aircraft may perform delegated ground separation procedures, especially in low-visibility conditions.
For high-demand airports, more efficient airport surface ops will yield an increase in total throughput. For lower-demand airports, staffed or automated virtual towers may be implemented, permitting services equivalent to those provided by traditional towers. Lower operational costs will allow these services at more airports than is affordable today and/or for extended hours.
Digital data communications
In tomorrow’s world of NextGen, voice communications will largely be replaced by digital data communications. Clearances, routine communications and 4DT agreements between ANSPs and the flightdeck will be handled digitally.
Except in rare instances, such as tactical situations caused by emergencies, voice communications between ANSPs and airborne traffic will be unnecessary. In addition, air-to-ground digital data communications will allow routine exchange of ATC clearances, surface movement instructions, current and forecast weather, hazardous weather warnings, Notams, electronic charts and special aircraft data such as engine trend data.
System-wide info management
Perhaps the hardest NextGen concept to understand is system-wide information management (SWIM). Basically, SWIM will make necessary infrastructure and services available to all decision-making parties and provide consistent, reliable and timely information for executing a flight, while accommodating national security needs.
Because current information (weather, Notams, closures, temporary flight restrictions, traffic flow, flight tracking, short and long-term 4DT intent, gate availability, etc) is network-enabled, and therefore accessible to all decision makers (flightcrews, dispatchers, ATC and individual subscribers), the speed and quality of decision-making will improve.
Common information distributed by a global Net-centric system will minimize duplication, achieve integration and facilitate shared decision-making. Net-centric information will flow freely between aircraft and the ground, as well as from ground to ground and aircraft to aircraft as needed.
Network-enabled weather
Most flight delays in the NAS today are caused by weather. Developing a network-enabled system of weather data gathering, interpretation, reporting and forecasting could reduce weather delays and their impact in the NAS by as much as 50%. This NextGen network-enabled weather (NNEW) will be an integral component of SWIM.
NNEW will provide a real-time, easy-to-interpret weather picture, constructed from tens of thousands of global ground observations. In addition, aircraft in flight and on the ground will input a constant stream of weather data into the system.
Individual aircraft will effectively become moving weather stations. Wind, temperature, water vapor, turbulence and icing data will stream constantly from aircraft-to-aircraft or aircraft-to-ground. Aircraft could also measure phenomena unrelated to weather, such as volcanic ash or radiation levels in the upper atmosphere, providing a clearer picture of flying conditions.
Environmental management
NextGen includes an environmental management element, designed to promote environmental responsibility and protection that will allow aviation to grow as predicted demand for air travel grows. For example, performance-based RNAV will cause aircraft to fly very precise departure/arrival tracks over the ground, resulting in fewer noise complaints.
Many airports will be able to accommodate continuous descent arrival (CDA) procedures. CDAs will allow aircraft to descend from the flight levels to the runway at lower thrust settings with no intermediate level-offs. This will reduce fuel consumption, noise and emissions.
UPS has been conducting CDAs into its SDF (Standiford, Louisville KY) hub as a demo program, using ADS-B equipped aircraft. The results have been dramatic. Overall noise has been reduced by 30% and emissions by 34%. Fuel savings of 40–70 gallons per arrival have been realized.
Improved airborne traffic flow will reduce arrival congestion and eliminate holding times, also resulting in fuel savings and reduced emissions. Net-centric weather will allow quicker decision-making during periods of rapidly changing conditions, resulting in better traffic flow, less holding time, reduced fuel burn and fewer emissions. Improved traffic flow management on the ground will result in shorter taxi times and reduced waiting times for takeoff clearances.
Although many of the components embodied in NextGen are still theoretical in nature, one thing is for certain—it is coming. We can already see that the first pieces of NextGen are being put in place today so an accommodating and dynamic NAS will be in full operation tomorrow.
Steve Oetzell is a retired Continental Airlines/ PEOPLExpress captain and a member of ALPA. He currently works as an airport certification/safety inspector in FAA’s Western-Pacific Region. In addition, Oetzell works together with members of the Runway Safety Program Team. He is type rated in the Fairchild Metro, Boeing 737, and Douglas DC9.
