A Review of the Next Generation Air Transportation System: Implications and Importance of System Architecture (2015)

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Recognize Constraints and Align Expectations

In 2003, an effort to transform the U.S. air transportation system was announced and the Joint Planning and Development Office (JPDO) was established by Congress to develop the Next Generation Air Transportation System (NextGen).¹ NextGen refers to a set of programs and initiatives to be coordinated into an evolving overall air transportation system aimed at a continuing transformation of the National Airspace System (NAS).² NextGen aims to overhaul the U.S. air transportation system through a combination of procedural and technological improvements. It is intended to make use of extant capabilities along with newer enabling technologies such as precision satellite navigation systems and a digital communications infrastructure to share real-time information. Effective use of these tools could make it possible to shorten routes, navigate better around weather, save time and fuel, reduce delays, increase capacity at airports not already capacity-limited by physical infrastructure, and improve capabilities for monitoring and managing of aircraft. The Federal Aviation Administration

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¹ The Joint Planning and Development Office (JPDO) was a multi-agency initiative created to oversee planning and coordination for NextGen. In 2014, funding for the JPDO was eliminated, and the FAA created a new Interagency Planning Office to replace it. See reporting on a statement FAA provided to AIN at B. Carey, “FAA’s New ‘Interagency Planning Office’ Replaces JPDO,” AIN Online, May 27, 2014, http://www.ainonline.com/aviation-news/air-transport/2014-05-27/faas-new-interagency-planning-office-replaces-jpdo.

² NextGen and other programs or initiatives of similar scale are sometimes referred to as “systems of systems.” Any system of systems is itself a system, and the committee has chosen in this report to use the term “system” for simplicity.

(FAA), working along with a wide range of stakeholders, is currently working toward both near-term and midterm capabilities.³

Section 212 of the Federal Aviation Administration Modernization and Reform Act of 2012, Public Law 112-95 (see Box 1.1), calls for an examination by the National Research Council (NRC) of NextGen’s enterprise software development approach and safety and human factors design. To respond to this request, the NRC formed the Committee to Review the Enterprise Architecture, Software Development Approach, and Safety and Human Factor Design of the Next Generation Air Transportation System in 2012 to conduct this study. In this final report, the committee provides its analysis and recommendations to the FAA with a particular focus on the importance of system architecture and its implications.

SCOPE OF REPORT

The committee was asked to address a broad suite of topics related to NextGen. The material in this chapter provides context and background on NextGen and provides some of the committee’s observations about how NextGen has, and has not, developed over time. Drawing on the technical expertise and experience of its members, the committee chose to use system architecture as an organizing principle through which to assess the input it received, to organize its recommendations, and to address its statement of task (Box 1.2). Chapter 2 explains this in detail. Point 1 of the statement of task asks the committee to consider a variety of factors with respect to transitioning to the future system envisioned by the JPDO. As described, that vision has been overtaken by subsequent events that took place before the committee first convened.

Accordingly, the committee discusses those factors as they relate to NextGen currently. Safety issues are discussed in Chapter 3, and human factors are discussed in Chapter 4. Point 2 of the statement of task asks the committee to consider risk, benefits, and software development. These topics are addressed in Chapter 4. Point 3 of the statement of task asks the committee to consider risks of automation and apply lessons from other entities. As noted above, NextGen as currently planned will not have significant amounts of new automation (as was envisioned by the early JPDO). Chapters 2, 3, and 4 offer the committee’s recommendations to the FAA on how to better manage planning and risk based on the committee members’ experiences in a variety of other domains.

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³ More information about NextGen can be found in the NextGen Implementation Plan, on the Federal Aviation Administration’s (FAA’s) website at http://www.faa.gov/nextgen/library/.

Questions that are relevant to all of these issues concern how the FAA should be organized, what its funding structure should be, and what governance structure is most appropriate for the agency as a whole. The committee believes there is much to be learned from exploring these questions, and they do bear significantly on planning and architecture for NextGen. However, that exploration was beyond the scope of this committee’s tasking, and thus the report does not address these questions directly.

During the course of this study, there were numerous other efforts under way related to NextGen planning. The Department of Transportation Inspector General issued a report urging sustained FAA leadership

and action to address NextGen delays.⁴ The Government Accountability Office also urged substantial leadership commitment and the empowering of leaders to make critical decisions.⁵ MITRE’s Center for Advanced Aviation Development—FAA’s federally funded research and development center—recently recommended six strategic focus areas to move forward with NextGen, the first of which emphasized the importance of transformational and foundational infrastructure.⁶ The committee’s final report here should be seen as complementary to these, emphasizing the

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⁴ Department of Transportation, Addressing Underlying Causes for NextGen Delays Will Require Sustained FAA Leadership and Action, Office of Inspector General Audit Report AV-2014-031, February, 25, 2014, https://www.oig.dot.gov/library-item/28823.

⁵ Government Accountability Office, “FAA Reauthorization Act: Progress and Challenges Implementing Various Provisions of the 2012 Act: Statement of Gerald L. Dillingham, PhD, Director, Physical Infrastructure,” Testimony Before the Subcommittee on Aviation, Committee on Transportation and Infrastructure, U.S. House of Representatives, GAO-14-285T, February 5, 2014, http://www.gao.gov/assets/670/660683.pdf.

⁶ MITRE Corporation, NextGen Independent Assessment and Recommendations, MP 140440, October 2014, http://www.faa.gov/nextgen/media/MITRE_NextGen_Independent_Assessment_and_Recommendations.pdf.

importance of system architecture and architectural leadership and drawing connections between architectural choices and broader outcomes.

WHAT IS NEXTGEN—ALIGNING EXPECTATIONS

Although technological and procedural improvements have been introduced into the NAS over the years to increase capacity, reduce delays, and improve safety, elements of the NAS rely on outdated technology. The system as a whole has not been significantly changed to take advantage of available information and communications technologies that could engender needed improvements in the security, robustness, and evolvability of the NAS and enable major improvements in how the airspace can be organized and managed.

There are numerous complex constraints on the design and operation of the NAS to which the FAA and its stakeholders are subject. The FAA is well aware of these constraints—some of which affect development of systems and some of which affect potential benefits and outcomes. Furthermore, the NAS exists in a complex political, organizational, and economic milieu that imposes its own constraints and demands as well. For example, few airports have the option to build additional runways; aircraft capacity decisions are solely in the hands of the airlines and manufacturers; and alternative competitive intercity transportation options, such as high speed rail or other ground transportation means, do not exist in most major cities—all of which continue to place increased pressure on Metroplex airports.⁷ In the committee’s view, it is helpful to keep these often challenging constraints, which include legacy commitments already made, in mind when planning, assessing, or evaluating NextGen efforts.

Throughout the committee’s work, it became clear that “NextGen” means different things to different people, ranging from a wide-ranging transformational vision to a much more concrete set of phased incremental changes to various parts of the NAS. With so many stakeholders and so many moving parts, different understandings of “what is NextGen” have arisen. The committee has come to a view of what NextGen is (and is not), and that view is described briefly below for the purposes of this report. Any particular definition is less important, however, than ensuring that all stakeholders understand each other’s expectations and

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⁷Metroplex refers to “a system of airports in close proximity and their shared airspace that serve one or more major cities. A metroplex has at least one, but often two or more major commercial airports.” They include the following: Atlanta, Boston, Charlotte, Chicago, Cleveland, Washington, D.C., Denver, Detroit, Houston, Las Vegas Valley, Memphis, Minneapolis-St. Paul, New York/Philadelphia, North Texas, Northern California, Orlando, Phoenix, Seattle, South Florida, Southern California, and Tampa. See FAA, “Metroplexes,” last modified August 26, 2014, http://www.faa.gov/Nextgen/snapshots/metroplexes/.

anticipated outcomes and that capabilities, plans, and requirements are aligned well.

The vision and concept of operation for NextGen was set forth in documents from JPDO. In particular, a 2004 Concept of Operations described at a very high level a desired end state for the NAS, and that description was developed in more detail in later versions.⁸ Briefings and documents provided to the committee have indicated the capabilities expected to be deployed in the “medium term” (a time frame defined by the FAA as “by 2018”). These plans call for the execution of several programs that provide new or replacement technology.

For example, Automatic Dependent Surveillance-Broadcast (ADS-B) provides a new, Global Positioning System (GPS)-based surveillance capability complementing and partially replacing existing surveillance radars.⁹ En Route Automation Modernization (ERAM) replaces the En Route Host computer system with new display, communications, and planning tools for air traffic controllers. An enhanced data communications system (Data Comm) will allow for incremental replacement of data-intensive communications between air traffic control and the flight crew with digital communications (such as transmitting flight plans to aircraft). The System Wide Information Management (SWIM) system enables the sharing of real-time digital information between different systems and stakeholders, such as carriers, airports, aircraft maintenance operators, and so on. Other programs relating to weather support services, air traffic management, and voice systems are also under way to support NextGen goals.

The existing documents and decisions specify solutions and technology but not operations. A standard good practice is that operations should be carefully defined independent of technological implementation. This is particularly important where value improvement comes from operational changes. New technologies under consideration imply changed operations to realize large value, but the FAA has not addressed this through a detailed operational analysis. Standard practice is that the “owning” organization should play close attention to the operational description

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⁸ See Chapter 4 of JPDO, Next Generation Air Transportation System Integrated Plan, 2004, http://www.dtic.mil/dtic/tr/fulltext/u2/a605269.pdf; JPDO, Making the NextGen Vision a Reality: 2006 Progress Report to the Next Generation Air Transportation System Integrated Plan, 2006, http://www.dtic.mil/dtic/tr/fulltext/u2/a502356.pdf; and JPDO, Version 2.0, 2007, http://www.dtic.mil/dtic/tr/fulltext/u2/a496134.pdf; JPDO Concept of Operations for the Next Generation Air Transportation System Draft 3 Version 1.1a, December 6, 2006; FAA NextGen Mid-Term Concept of Operations for the National Airspace System, Version 2.0, April 30, 2010.

⁹ Automatic dependent surveillance-broadcast (ADS-B) is an aircraft tracking technology that relies on the global positioning system (GPS) and a datalink to broadcast (ADS-B Out) and receive (ADS-B In) data.

and should “own” the operational description, even where technology choices may be deferred to contractors. This topic is discussed further in Chapter 2.

An additional challenge is that considerable confusion on the part of non-FAA observers and stakeholders has resulted from ambiguous use of the NextGen label. At times, it has been used to mean the full, original JPDO vision; at other times, as a collective name for all the activities of the NextGen office, including basic modernization and replacement of existing facilities; and on occasion as a shorthand for “later than 2020.” In the committee’s view, NextGen, as currently instantiated, is a set of programs to implement a suite of incremental changes to the NAS. Although some technologies and/or systems will be new, in most cases, current plans call for them to be used in a way nearly identical to existing capabilities. NextGen’s implementation plan employs a strategy that can be described as: “design a little, build a little, test a little, deploy a little.” This aspect of the plan is understandable and reflects lessons learned from past efforts¹⁰ as well as an industry-wide best practice of incremental change and development.

An important part of NextGen is addressing urgent requirements to replace aging equipment. Such modernization is essential and important, as the committee noted in its interim report.¹¹ NextGen also includes efforts to further deploy performance-based navigation, to redesign certain aspects of the airspace (such as rules and procedures and altitudes and headings), and to equip aircraft with technology (such as ADS-B) that can form the basis for future capabilities. NextGen has also come to encompass an additional broad range of activities expressed in various implementation plans, the NAS enterprise architecture, roadmaps, and calls for research, experimentation, and further incremental programs. Replacing or upgrading systems while the whole system must continuously and safely operate is an intricate undertaking, a process that the FAA seems to have mastered. These are complex systems that are undergoing constant change as aging equipment is replaced, as software is altered to improve resilience, and as operational requirements change. The successful operation of such systems requires ongoing alteration

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¹⁰ Such as the FAA’s Advanced Automation System—a failed modernization effort begun in the 1980s that did not recognize the complexity associated with making major changes to software intensive national-scale systems. That effort resulted in significant delays and cost overruns, due in part to unrealistically ambitious goals without complete stakeholder agreement.

¹¹ National Research Council (NRC), Interim Report of a Review of the Next Generation Air Transportation System Enterprise Architecture, Software, Safety, and Human Factors, The National Academies Press, Washington, D.C., 2014.

and improvement, not just the occasional repair of faulty equipment and software.

NextGen is not, however, broadly transformational. That is, it does not set out a series of planned steps toward a fundamentally transformed end-state (such as free flight, decommissioning surveillance radar stations, automating air traffic control processes with a completely digital information infrastructure, or shifting authority from ground to air). And thus it is not an implementation of the early JPDO vision, which encompassed those ideas.¹² The executive order establishing the JPDO was entitled “Transformation of the National Air Transportation System,”¹³ and early vision documents referred to ambitious goals such as integrated data streams for situational awareness in seamless multi-agency global operations, scalability, the use of emerging space-based communications and surveillance technologies.¹⁴ Not all parts of original JPDO vision will be achieved in the foreseeable future. This was true even at the outset of NextGen and is understandable, given changes over time.¹⁵ However, even the limited vision embraced at the start of NextGen has been reduced over time, while increasingly important challenges have not received adequate attention.¹⁶ Many of the specific goals described in early JPDO discussions, such as free flight or air traffic control based on predefined 4-D flight trajectories, to enable global optimization of the airspace will not come to fruition in the foreseeable future. In fact, many of them will require significant research and experimentation before it can be known whether and in what form they are feasible. Unfortunately, over the course of the committee’s work, it was clear that some stakeholders were still anticipating these capabilities from NextGen. Such goals await the now-distant full deployment of technical capabilities, the integration of these capabilities to support higher levels of automation and more distributed and autonomous operation, full equipage of virtually all aircraft with new components, and widespread revisions to procedures. More importantly, however, they will await the organizational will to

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¹² Expressed in JPDO’s “Concept of Operations for the Next Generation Air Transportation System,” Version 3.2, 2011, http://www.dtic.mil/dtic/tr/fulltext/u2/a535795.pdf. See also Appendix B of the 2005 NRC report Technology Pathways: Assessing the Integrated Plan for a Next Generation Air Transportation System (The National Academies Press, Washington, D.C.) for an overview of JPDO objectives.

¹³ White House, “Transformation of the National Air Transportation System,” Executive Order, released November 18, 2008, http://georgewbush-whitehouse.archives.gov/news/releases/2008/11/20081118.html.

¹⁴ See Appendix B of the 2005 NRC report Technology Pathways for an overview of JPDO objectives.

¹⁵ For instance, the substantial future demand growth anticipated in early planning did not materialize.

¹⁶ For instance, cybersecurity was not a significant concern in early JPDO planning.

modify the human roles and responsibilities of the participants in the NAS in order to meaningfully exploit the possibilities offered by these technologies.

A number of constraints may have plausibly contributed to the scaling back of NextGen ambitions, at least for the foreseeable future. These include the following:

• Recognition that NextGen cannot fully remediate key NAS capacity limits. Congestion in the NAS tends to be localized to certain regions, with more than one-half of activity in the approximately 20 so-called Metroplex sites, where the number of runways is a fundamental constraint on NAS throughput. Although there are opportunities to increase runway efficiency, such as some reduced separation, more parallel approaches, and so on, the realizable benefits of such are not yet clear. For example, wake vortex separation requirements may limit separation reduction, and local community resistance to noise and night flights may limit the introduction of new approach routes or extended hours that would increase the capacity of existing runways. In addition, new runways would be required to meet some capacity projections in certain locations.¹⁷
• Uncertainty about future demand growth. NAS capacity needs are hard to predict. Business dynamics, passenger demand and fuel costs are changing dramatically. The economic cycle in the 2000s weakened the capacity case for making wholesale changes in the NAS.
• Impediments to the introduction of more automation, more distributed control, and significant changes to procedures. Factors such as resistance (whether direct or due to cultural inertia) to significantly altering the nature of controller work, a conservative safety culture that makes changes to procedures slow and expensive, and limited resources and capacity to implement widespread changes to procedures have stalled efforts to make the fundamental changes to the concept of operations that the JPDO envisioned. It is difficult to distinguish specifically how much each of these factors contributes, but it will be critical to address these organizational and cultural factors if full advantage is to be taken of new technological possibilities.¹⁸

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¹⁷ See, for example, Transportation Research Board, Airport Cooperative Research Program: Evaluating Airfield Capacity, 2012, http://onlinepubs.trb.org/onlinepubs/acrp/acrp_rpt_079.pdf, and FAA, FACT3: Airport Capacity Needs in the National Airspace System, 2015, http://www.faa.gov/airports/planning_capacity/media/FACT3-Airport-Capacity-Needs-in-theNAS.pdf.

¹⁸ The 2014 NRC report Autonomy Research for Civil Aviation: Toward a New Era of Flight (The National Academies Press, Washington, D.C.) explores increasingly autonomous systems and their implications for civil aviation.

In short, NextGen will not provide a means to, say, double air traffic capacity by 2025,¹⁹ nor does it offer a way to address increasingly urgent requirements for strengthened security, greater robustness, and evolvability to meet new challenges, such as addressing projected unmanned aircraft systems (UAS) traffic. NextGen is also not currently expected to significantly change roles in place today (e.g., giving pilots more authority). While many readers of this report will find these assertions obviously true, during its investigations, the committee heard references to and vestiges of these ambitious goals. It is appropriate for NextGen goals and aims to have changed over time, and in some cases there were ambitions informally affiliated with NextGen that were not actually ever part of the NextGen effort. That being the case, it seems appropriate for the FAA, working with stakeholders, to clearly circumscribe these goals and ambitions and to clearly articulate the program’s actual current goals and ambitions.

With only modest changes to the operation of the NAS through 2018, NextGen programs are better described as a technology-refresh effort rather than the transformational activity envisioned by JPDO. This understanding does not undermine the critical importance of NextGen, because its programs will replace and modernize critical components of the NAS that would otherwise become increasingly difficult and expensive to maintain as a result of age. Thus the bulk of the currently pursued programs labeled as “NextGen” are properly thought of as a necessary and inevitable upgrade to existing technology, supporting essentially unmodified operating practices. Nevertheless, there are things that can be done now to help ease the path toward eventual significant change. For instance, a few of the NextGen programs introduce technologies that, if properly embraced by a future-oriented system architecture, could form the basis for transformation and pave the way toward more ambitious goals. New technologies such as ADS-B and digital communication are important digital infrastructure for future enhancements, but their potential is masked by other impediments, such as those cited above.

The committee’s conclusion that NextGen today is primarily an incremental modernization effort should not suggest that NextGen, therefore, has an obvious completed state. Given the continuing rapid pace of technological evolution and ongoing changes in what is demanded of the NAS (see Chapter 4 for a discussion of UAS and cybersecurity as examples),

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¹⁹ Early planning documents used to motivate NextGen noted that some models projected that the number of passengers could more than double by 2025 (see, for example, Gisele Mohler, FAA, “Airport Capacity Planning and NextGen,” presentation to the Eastern Region Airport Conference, March 2008, http://www.faa.gov/airports/eastern/airports_news_events/hershey/media_08/Mohler-Eastern%20Region%20Arpt%20Conf08%20-GM.pdf).

the NextGen effort is properly seen as an ongoing process, punctuated by particular efforts focused on particular capabilities. Such an effort will require an appropriate systems architecture (discussed in Chapter 2) and a risk-managed development process (discussed in Chapter 4).

Much has changed even in the course of the committee’s work, including the appointment of a new assistant administrator for NextGen. In a recent report to Congress, the FAA has presented a more realistic indication of what NextGen is relative to what it was envisioned (i.e., how far it has been scaled back).²⁰ The committee urges that a clear realignment of expectations for all parties take place. Revised expectations should not only concern what the future state of the NAS will be, but also reflect the kind of evolvability that needs to be built into the system so that later technologies (which may either come along or be modifications of planned technologies), new requirements, and changing market conditions can be exploited. Resetting expectations with a clear baseline will provide a useful foundation on which to build.

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²⁰ FAA, NextGen Priorities Joint Implementation Plan: Executive Report to Congress, October 2014, http://www.faa.gov/nextgen/media/ng_priorities.pdf.