Future Flight: A Review of the Small Aircraft Transportation System Concept -- Special Report 263 (2002)

In this chapter, the National Aeronautics and Space Administration’s (NASA’s) concept of a Small Aircraft Transportation System (SATS) and the main elements of its 5-year program to evaluate and demonstrate technologies leading up to the envisioned system are summarized. The key findings from the analysis of the SATS concept are then described. On the basis of these findings, the committee offers its conclusions concerning the use of the SATS concept to guide technology development and deployment. Finally, recommendations on ways to improve the SATS program by making it more responsive to the needs of aviation users and the public are given.

Among the overarching goals of NASA’s Office of Aerospace Technology are to “revolutionize aviation,” “enable people to move, faster and farther, anytime, anywhere,” and “reduce inter-city doorstep-to-destination transportation time by 50 percent in 10 years and by 67 percent in 25 years.”¹ With these goals in mind, NASA has set forth a vision under which advanced small aircraft, of a size commonly used in general aviation (GA) today, will be flown routinely between the country’s small GA airports, transporting individuals, families, and groups of business travelers. The vision anticipates major advances in avionics, engines, airframes, flight control, manufacturing, communications, and navigation systems and their application to thousands of small fixed-wing aircraft over the next several decades. These advanced aircraft will be safer and easier to operate and much more comfortable, reliable, and affordable than GA aircraft today. The enhancements will make many more of the country’s 5,000 small airports much more practical and available for intercity transportation without requiring large public investments in airport and air traffic control infrastructure.

To further this concept, NASA has received funding ($9 million for FY 2001) from Congress to begin a 5-year program to identify, develop, and demonstrate “key airborne technologies for precise guided accessibility in small aircraft in near all-weather conditions to virtually any small airport in non-radar, non-towered airspace.”² Specifically, Congress has charged NASA with collaborating with the

private sector to develop and evaluate technologies that can provide the following four capabilities:³

• High-volume operations at airports without control towers or terminal radar facilities,

• Lower adverse weather landing minimums at minimally equipped landing facilities,

• Integration of SATS aircraft into a higher en route air traffic control system with complex flows and slower aircraft, and

• Improved ability of single-pilot aircraft to function in complex airspace in an evolving national airspace system.

The SATS program to demonstrate these capabilities, which NASA estimates will require approximately $69 million in government funding over the 5-year period, is now under way. The program plan states that the goal of the public-private partnership program is to provide “the technical and economic basis for national investment and policy decisions to develop a small aircraft transportation system.” The first phase will entail development of technologies pertinent to each of the congressionally identified capabilities, including technologies for aircraft separation and sequencing, software-enabled controls, emergency automated landing, and highway-in-the sky guidance. Candidate technologies in each area will be screened and selected for further development and evaluation. In the program’s final year, NASA hopes to integrate technologies to exhibit three or more of the capabilities in a public demonstration that includes flight demonstrations. It also plans to assess the economic viability, environmental impacts, and community acceptance of an “end-state” SATS.

NASA has offered two main justifications for pursuing and promoting this concept. The first is that SATS would increase transportation system capacity by shifting travel demand from the most congested parts of the aviation system to more lightly used parts without requiring significant infrastructure investment. The second is that SATS would enhance and extend air service to many small communities. The committee’s analyses of the potential for SATS to achieve these goals, while also meeting other public-interest goals such as ensuring transportation safety and environmental compatibility, raise many uncertainties and questions about the SATS premise and led to the following conclusions:

• There is little evidence to suggest that SATS aircraft can be made affordable for use by the general public. The aircraft envisioned for SATS would need to be far more advanced and sophisticated than even the highest-performing small GA aircraft of today to achieve the standards of safety, ease of use and maintenance, and environmental friendliness that would attract large numbers of users. The committee found no evidence to suggest that such aircraft could be made affordable for use

by large numbers of people and businesses. The complexity and cost of manufacturing GA aircraft have typically increased as aircraft capabilities have improved and expanded. The aircraft industry has not yet demonstrated a strong potential for volume-related economies that might greatly lower the cost of producing such advanced aircraft in large quantities. Although they lack nearly all of the advanced capabilities envisioned for SATS, the smallest jet aircraft in the early stages of pre-production planning today are projected to sell for about $1 million each. The least expensive small aircraft—and those best suited for use in most small airports—are piston-engine propeller airplanes. These aircraft do not appeal to most travelers because of their interior noise and vibrations, inability to fly well above most weather, frequent maintenance, and poorer safety record than jets.

• SATS has minimal potential to attract users if it does not, as conceived, serve the nation’s major metropolitan areas. The expectation that large numbers of people will use advanced small aircraft to fly between airports in small, nonmetropolitan communities runs counter to long-standing travel patterns and demographic and economic trends. Most people and businesses are located in metropolitan areas, which are the origins and destinations of most intercity passenger trips. These patterns have strengthened over time, even as transportation and communications systems have improved. Metropolitan areas account for a large majority of all business travelers, as well as higher-income households, which have a high propensity for air travel. The committee found no evidence, only speculation, to suggest that these patterns are changing or likely to change as a result of the emergence of a new transportation system centered on the use of small airports and advanced small aircraft. Because the nation’s large metropolitan areas account for most commercial airline traffic, they present a highly complex operating environment for small, private aircraft—a significant challenge for SATS application. An intercity transportation system that does not serve these markets will, in effect, neglect the largest and most likely pool of prospective users.

• SATS promises limited appeal to price-sensitive leisure travelers, who make most intercity trips. Most intercity travelers are highly sensitive to the price of travel, especially in the short- to medium-length trip markets envisioned for SATS. Leisure travelers, who account for the majority of all intercity trips under 1,000 miles, usually travel by automobile, largely because of the versatility it offers and the low additional cost per passenger. In general, air service frequency, speed, and convenience are less important attributes to leisure travelers than they are to business travelers, who are often willing to pay a premium for such service, while leisure travelers will not. In addition to being inexpensive to operate, automobiles have other qualities that are highly valued; for instance, they can carry large amounts of baggage, provide door-to-door transportation, and offer a means of local transportation at the destination. Because SATS is envisioned as a common mode of transportation for short to medium-length trips, these competitive disadvantages relative to the automobile present major shortcomings.

• Infrastructure limitations and environmental concerns at small airports are likely to present large obstacles to SATS deployment. Most of the country’s 5,000 public-use airports have minimal infrastructure and support services, which limits their suitability for frequent and routine transportation usage. About half of

public-use airports have a paved runway that is at least 4,000 feet long and thus potentially capable of handling small jet aircraft; yet, most of these airports would likely require further infrastructure investments. Few public-use airports, for instance, have on-site fire and rescue stations or intensive programs for monitoring and maintaining runway condition. While travelers appreciate airport proximity to their points of origin and destination, they also value airport services, such as ground transportation, automobile parking, and passenger waiting areas. Travelers are willing to sacrifice some proximity to obtain such services, which are costly and impractical to provide at airports with limited passenger volumes. Of the nation’s 2,800 top-quality GA airports that receive federal aid, more than 70 percent are located within 75 miles of a commercial-service airport offering scheduled airline service and passenger facilities and services. Most GA airports with sophisticated infrastructure and services are located in large metropolitan areas and are heavily used. Most public-use airports located more than 75 miles from a commercial airport are situated in rural areas and have limited potential to attract users. Without information to indicate otherwise, it is reasonable to assume that these small airports are best suited to accommodate the level and mix of traffic activity existing today. Significant changes may require infrastructure modifications as well as investments to address noise and other environmental concerns that have proved to be major impediments to the expansion of airports of all sizes and types.

• Many technical and practical challenges await the development and deployment of SATS technologies. Safety is paramount in aviation, particularly for passenger transportation. Hence, any changes in aviation, from new methods of air traffic control and pilot training and certification procedures to new aircraft materials and manufacturing processes, are subject to intense and thorough safety evaluations and validations that can take much time. The idea that many nonevolutionary changes in aircraft design, propulsion, flight control, communications, navigation, surveillance, and manufacturing techniques could emerge at about the same time and be accepted as safe by users, manufacturers, insurers, and regulators is highly questionable. Assessing and ensuring the safety of any one of the new capabilities and advanced technologies envisioned for SATS would likely present many technical and practical challenges. The idea that many such changes could occur almost simultaneously in a new operating environment with a much different pool of pilots seems unreasonable without assuming a fundamental change in safety expectations and procedures. The magnitude of this safety assurance challenge alone, which has been largely neglected in the NASA program, is sufficient to call into question the plausibility of the SATS vision.

• SATS has the potential for undesirable outcomes. If SATS does not access major metropolitan markets, it will likely have little, if any, meaningful effect on operations at the nation’s busiest and most capacity-constrained large airports, where most delays in the commercial air transportation system occur. Yet, if SATS does access these markets, the mixing of SATS with non-SATS aircraft in heavily used, controlled airspace and airports could create significant traffic management challenges. Moreover, a well-used SATS could have negative net effects on aviation’s environmental compatibility by shifting travelers from larger aircraft, each carrying dozens of travelers, to smaller aircraft, each carrying a handful of travelers. Such a

shift, resulting in a net increase in aircraft operations to carry the same number of travelers, would almost certainly increase aggregate energy use as well as emissions of various pollutants and would have other environmental impacts, even if SATS vehicles offered considerable gains in fuel efficiency. A shift in aviation activity to small, currently underutilized airports could also result in increased impacts to natural resources in the vicinity of the airports, including bodies of water, wetlands, and sensitive habitat. These possible outcomes of SATS have gone largely unexamined.

NASA asked the study committee to answer the following two questions:

1. Do the relative merits of the SATS concept, in whole or in part, contribute to addressing travel demand in coming decades with sufficient net benefit to warrant public investment in technology and infrastructure development and deployment?

2. What are the most important steps that should be taken at the national, state, and local levels in support of the SATS deployment?

As explained in Chapter 1, the committee interprets the first question as a request for an assessment of whether the SATS concept is sufficiently plausible and desirable to serve as a guide for government investments in technology development and deployment. The second question asks how public investment in those aspects of the SATS concept that have merit—assumed to mean the component capabilities and technologies of SATS—can best be accomplished.

In answer to the first question, the committee finds that the full-scale SATS concept presents a highly unlikely and potentially undesirable outcome. The findings summarized above suggest that such a system is not likely to emerge as conceived or contribute substantially to satisfying travel demand. It is limited by the affordability of the conceived vehicles, the lack of demand between origin and destination points proposed in the concept, and complex system issues ranging from airspace design and management to safety and environmental effects. The potential for such a system to induce significant new travel demand is speculative. Moreover, the committee believes that the positing of any such preconceived system, in which a single and definitive vehicle concept is used to guide research and development, could inhibit the evolution of alternative outcomes that may result from technological opportunities and economic and social need.

In answer to the second question, the committee views favorably and endorses much of the technological research and development contained in the SATS program, as well as the approach of using NASA and other government resources and expertise to leverage and stimulate private-sector investment in aeronautics research and development. The committee does not, however, support public-sector investment in SATS deployment or the use of the SATS concept itself as a guide for making technology development and deployment decisions.

There is reason to believe that the component capabilities and technologies being pursued now under the SATS umbrella can enhance safety and confer other benefits on users of both general and commercial aviation. The committee’s recommendations

for better orienting these research and technology efforts toward achieving such public benefits are given in the next section.

Aviation has a crucial role in the nation’s transportation system, and the public sector has a large influence on it. The federal government funds and operates the nation’s airspace system and sets standards governing the design, manufacture, maintenance, and operation of aircraft. It works with state and local governments to help finance the nation’s airports and to ensure aviation’s safety and environmental compatibility. Therefore, the public sector has reason to have a keen interest in sponsoring research on technologies that can make civil aviation safer, reduce its potential harm to the environment, and improve its overall productivity and efficiency.

NASA has traditionally played an important role in supporting and conducting this research on behalf of the federal government. However, NASA’s strength in civil aeronautics is in technology research and development, and not in defining, developing, and promoting new transportation systems. Accordingly, the committee urges NASA to join with other relevant government agencies, led by the U.S. Department of Transportation, in undertaking forward-looking studies of civil aviation needs and opportunities to ensure that they are being addressed appropriately through government-funded technology research and development. Working with the Federal Aviation Administration (FAA), the National Transportation Safety Board, and other government agencies with operational and technological expertise, NASA should gain a better understanding of these needs and how to structure aeronautics research and development to help meet them.

It is crucial that major elements of NASA’s technology research be supported by a strong empirical understanding of important civil aviation needs. The technological capabilities now being pursued under the SATS program offer the potential to address some such needs; for instance, by allowing more reliable and safe operations during inclement weather at more small airports and by improving the accuracy, timeliness, and relevance of the weather, traffic, and airport information provided to GA pilots. Therefore, the committee believes that NASA should continue its efforts to advance these capabilities; however, it should orient the program goals toward toward realistic views of transportation operations and needs, rather than furthering the unpromising SATS concept. Thus, the committee recommends that NASA prioritize the capabilities and technologies that are now being pursued in the SATS program according to a clearly defined set of civil aviation needs that these capabilities and technologies can help meet. Progress in meeting such needs through advanced technology will likely have other positive effects such as improving the overall utility of small aircraft in transportation. However, such outcomes, which are uncertain, should not justify or guide the technology program. A safer, more efficient, and more environmentally acceptable GA sector is likely to have greater utility, whatever the specific form it takes.

To be sure, NASA ought to be concerned that the technologies that it does pursue are practical from the standpoint of commercialization and do not have unacceptable side effects. Thus, NASA should work closely with commercial developers and users. The private sector understands the market for technologies, at least in regard

to current operations, and can provide guidance on applications that appear likely. The level of interest by commercial developers and users can help determine which technology developments merit further attention. Likewise, NASA must continue to involve FAA and state and local agencies in evaluating this technology program. Their involvement is essential to understanding constraints on technology deployment, such as noise, energy efficiency, air pollutant emissions, safety, public finance, and other environmental and social concerns.

The SATS concept has been presented as a way to provide the public with benefits through an expansion of usable airport and airspace capacity without the need for large public-sector investments. The committee did not find justification for this expected outcome and therefore urges NASA to put aside the SATS concept and recommit the program to other, more achievable, goals. The capabilities and technologies being developed under the SATS program may prove useful in ways that are not now apparent. Indeed, many system and vehicle configurations not envisioned for the current SATS concept may emerge. The committee urges NASA to keep such possibilities in mind.

Finally, on the basis of the findings from the review of this program and reviews by others of similar activities,⁴ the committee recognizes that technology research programs may become oriented toward justifying and furthering particular areas of research without adequately reflecting a connection with real-world needs. The committee commends NASA for requesting this review, which offers the opportunity for the perspectives and advice of experts in transportation and other disciplines not involved in the conception of SATS to be brought to bear. Additional external reviews of program goals and the technical progress toward achieving them are desirable as the restructured program proceeds.

TRB Transportation Research Board

TRB. 1998. Special Report 253: National Automated Highway System Research Program: A Review. National Research Council, Washington, D.C.