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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 3 Air Transportation Challenges: Enhancing Capacity, Service, Safety, and Environmental Compatibility As discussed in Chapter 1, the Small Aircraft Transportation System (SATS) concept originated as a guide for the general aviation (GA) technology programs of the National Aeronautics and Space Administration (NASA). NASA foresees the application of advanced technologies to small aircraft to make them much easier to pilot, more reliable, safer, and less expensive to own, maintain, and operate than high-performance GA aircraft today. It envisions tens of thousands of advanced small aircraft being flown in the nation’s uncontrolled airspace for personal transportation between thousands of small GA airports that are lightly used today. More than envisioning such a system, NASA is promoting it through research and technology partnerships with industry, universities, the Federal Aviation Administration (FAA), and state and local aviation authorities. The main rationale for promoting SATS is that it could help alleviate congestion and delay in the commercial aviation sector and increase transportation options for people and businesses residing in many small and remote communities with limited access to airline service. Reducing congestion and delay in the air transportation system is a decades-long public policy goal that has become more urgent in recent years as air travel demand has escalated. Likewise, access to more reliable, convenient, and affordable air transportation has been a long-standing aim of many small communities eager to attract economic development but unable to afford or justify large public investments in airport infrastructure. The prospect of increasing aviation system capacity and coverage through advanced technologies applied to private small aircraft with minimal public infrastructure investment is appealing, but it warrants more careful review. In this chapter, the sources and magnitude of the congestion and capacity challenges facing the air transportation industry are examined. To better judge whether SATS can help increase system capacity and reduce congestion—and thus lessen the need for future public investments to expand airport and airspace capacity—it is necessary to understand the nature of the congestion problem and the quality and coverage of the service now being provided. The challenges facing the air transportation sector extend beyond the need to alleviate congestion and enhance service quality and coverage. Two particularly important challenges are the need to ensure air transportation system safety and environmental compatibility. The individual technologies and capabilities being furthered by NASA and its research partners have the potential to improve safety and environmental aspects of GA. Whether the envisioned system has the potential for
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 overall improvements in the safety and environmental compatibility of air transportation, however, must be examined before concluding that the SATS concept is a desirable outcome. In this chapter, the following four aviation challenges are reviewed: alleviating congestion and delay in commercial air transportation, improving small-community access to air transportation service, enhancing aviation safety, and ensuring aviation’s environmental compatibility. This information is used in Chapters 4 and 5 to analyze the SATS concept. CONGESTION AND DELAY IN COMMERCIAL AIR TRANSPORTATION While ensuring security is the foremost challenge facing the aviation sector, the efficient use and allocation of the nation’s airspace and airport capacity remain as long-term public policy imperatives. During the past decade, flight delays caused by system congestion and other factors have been a chronic source of frustration and cost for air travelers and the aviation industry. Delays are the most common passenger complaint received by the U.S. Department of Transportation (DOT), accounting for about 40 percent.1 According to DOT’s Inspector General, roughly one flight in four in 2000 was delayed, canceled, or diverted for reasons ranging from airport and airway congestion to severe weather and aircraft mechanical problems (DOT 2000). More than 1.3 million flights arrived late at their destinations—52 minutes late on average—adversely affecting about 160 million passengers. FAA and the Air Transport Association, which represents major airlines, estimate that airlines and their passengers incurred more than $5 billion in delay-related costs.2 Recurrent delays and the unpredictability of schedules in the commercial aviation system are major problems for airlines and air travelers. The growing popularity of business jets and the introduction of fractional ownership programs are attributable in part to the desire of some travelers to obtain more reliable service and, in some cases, to avoid the crowds and congestion at major airports. Whereas the incidence of delay varies by individual airport, city, and region of the country, delays in one location can have effects that cascade throughout the entire system, since aircraft and passenger flows are interconnected. Understanding the causes of delay is complicated because of the large number of possible causes and the interconnectivity of the system; nevertheless, such an understanding is essential for devising solutions. Tracking the Incidence, Severity, and Source of Delays To monitor the performance of its air traffic management system, FAA collects data on flight delays through its Operations Network (OPSNET). FAA personnel manually record aircraft that are delayed for 15 minutes or more relative to their planned flight times3 after coming under FAA’s air traffic control (for instance, once the pilot has requested FAA clearance to taxi out for departure). Delays are recorded for arrival, departure, and en route operations; delays attributable to an airline’s own 1 DOT Air Travel Consumer Report, available on DOT’s website (www.dot.gov/airconsumer). 2 See DOT’s Audit Report (DOT 2000) and the Air Transport Association’s website (www.air-transport.org). 3 That is, relative to airline flight plan times with FAA, which may differ from the times listed in published schedules.
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 operations, such as aircraft maintenance, passenger boarding, or a late-arriving flight crew, are not recorded since they do not pertain to air traffic control performance. Likewise, canceled flights, from whatever cause, are not counted in OPSNET. Using OPSNET data, FAA defines an airport as suffering from significant delays when 3 percent or more of flights in the air traffic control system are delayed on arrival or departure for at least 15 minutes. Of the 31 busiest U.S. airports (in terms of passenger enplanements) in 2000, 8 exceeded this threshold (in some instances by a wide margin), accounting for two-thirds of all OPSNET-recorded delays at these 31 airports (see Figure 3-1). The eight airports handled nearly one-quarter of total U.S. passenger enplanements in 2000 (see Figure 3-1). By FAA’s measure, however, most of the country’s largest airports did not suffer from recurrent delays related to air traffic control. FAA records OPSNET delays as caused by one of five factors: (a) weather, (b) air traffic control or airport equipment problems, (c) closed runways or taxiways, (d) high flight volumes in the terminal area or regional traffic control center, or (e) “other.” Such classifications are complicated by the fact that delays are sometimes attributable to multiple causes and contributors. For instance, when inclement weather requires changes in air traffic control procedures, high traffic volumes can leave little, if any, margin for adjustment without incurring delays that propagate throughout the system, affecting flights in locations without severe weather. Weather is in fact the main source of flight delays associated with air traffic control, causing more than two-thirds of departure and en route delays in 1999 and 1998 (see Figure 3-2). The next most common cause, high traffic volume, is the primary source of delay in 12 percent of delayed flights. Because FAA’s OPSNET data do not include late flights (or flight cancellations) caused by delays in refueling, passenger boarding, baggage loading, maintenance, or other airline-related activities, the data do not fully reflect the experience of travelers. To derive a more complete picture of delays at the nation’s largest airports, DOT compares actual departure and arrival times with those published in airline schedules. Flights are reported as delayed when they do not pull back from the gate within 15 minutes of the scheduled departure time or to the gate within 15 minutes of scheduled arrival time. Although airlines have increased the time shown between arrivals and departures (“block times”) in their published schedules to better reflect actual experience, the DOT data show how airports differ in the incidence of delay. Whereas FAA’s OPSNET data indicate that delays affect 1 to 10 percent of operations at most large airports, the on-time performance data collected by DOT indicate that delays affect 15 to 30 percent of flights.4 These data suggest that air traffic control and capacity shortcomings account for only a portion of delays and that other factors, including airline operations, are important causes. Hence, improvements in airport infrastructure and air traffic control performance could reduce delays but would not affect all—or even most—flight delays. The use of hub-and-spoke systems affects the incidence and severity of delays. Although these systems have proved to be highly efficient in configuring air transportation networks, they contribute to the strains placed on the national airspace 4 See April 2001 release of DOT’s Air Travel Consumer Report, available on DOT’s website.
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 Figure 3-1 Flight delays and passenger enplanements at 31 busiest U.S. airports, percent of total by airport. (Source: FAA 2001.)
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 Figure 3-2 Causes of flight delays in the national air traffic control system, 1996–2000. [Source: OPSNET data (FAA 2000a).]
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 system, particularly at some of the major hub airports that serve as transfer points for much of the traffic in the system. As explained in Chapter 2, nearly all airlines funnel most of their flights and passengers through a small number of large hub airports. The largest transfer hubs handle more than 2,500 departures and landings and enplane more than 75,000 passengers per day. Indeed, on any given day, about 30 percent of all people flying on domestic airlines will arrive or depart on a flight at one of four airports: Chicago O’Hare, Los Angeles, Dallas–Fort Worth, or Atlanta. About 150,000 travelers begin or end their trips at one of these airports each day (representing 13 percent of all passenger trips), and another 210,000 pass through them on their way to other destinations. The occurrence of these clustered transfers, known as connecting banks, creates an uneven distribution of demand on the hub airports. Flights arrive and depart in waves that can exceed runway, taxiway, gate, and air traffic control capacity, especially if combined with inclement weather or other conditions that restrict capacity. Figure 3-3 shows the fluctuation in morning arrivals at Dallas–Fort Worth. Many of the peaks, occurring in 15- to 30-minute intervals, exceed optimal throughput capacity, which can force some arrivals to be delayed to nonpeak times. When runway capacity is severely diminished at a large hub airport, air traffic controllers often institute “ground holds” that can delay aircraft departing from scores of other airports. Challenges Since 1990, the number of domestic airline enplanements has increased by more than 40 percent. FAA expects airline passenger traffic to grow another 1.5 to 5.5 percent per year in the nation’s largest airports over the next 15 years, resulting in a 40 percent increase in total passenger enplanements by 2015 (FAA 1999; FAA 2000b). Likewise, the number of airline operations managed by traffic control towers is expected to rise by 30 percent in total and at even higher rates at several major airports, such as Atlanta, Minneapolis, Las Vegas, and Seattle. Escalating passenger traffic raises the prospect of greater demands on scarce runway space at major airports and on air traffic control, which could exacerbate system congestion and delay. It is important to recognize, however, that worsening aviation congestion because of traffic growth has been a concern for decades and that the aviation system has, by and large, responded without crises. Severe congestion at Washington’s National, Chicago’s O’Hare, and New York’s John F. Kennedy and La Guardia Airports during the late 1960s prompted the federal government to limit the number of daily landings and takeoffs at these airports. Airports elsewhere have been able to adapt without such artificial restraints because of continued enhancements in their operational capabilities and those of air traffic control and airlines. In the meantime, airports in fast-growing cities like Orlando, Las Vegas, and Charlotte have become major points of origin and destination, absorbing much of the growth in the system, which handles four times more passengers today than it did 30 years ago. Future strategies for enhancing system capacity to meet growing traffic demand are likely to center on the removal of chronic bottlenecks in the system, which would be achieved through targeted improvements in airport infrastructure, air traffic control
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 Figure 3-3 Distribution of morning flight arrivals at Dallas–Fort Worth (DFW) International Airport. (Source: FAA 2000a.)
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 capabilities and procedures, and airline operating practices.5 For example, increasing runway capacity at San Francisco International Airport (SFO), one of the busiest airports in the country, would do much to reduce flight delays throughout the system. SFO, which suffers from one of the highest occurrences of delay among major airports, accommodates about the same number of airline operations per year as Pittsburgh (PIT); yet PIT, which suffers relatively little delay, can handle many more operations per hour (see Figure 3-4). A particular problem for SFO is that it loses nearly one-third of its runway capacity during inclement weather, which is a frequent occurrence. FAA expects passenger traffic at SFO to grow by more than 60 percent during the next 15 years; hence, addressing its capacity problems—as well as those of several other large airports with similar problems—is considered critical to controlling the incidence and severity of delays in the wider system. One of the most effective ways to increase national airspace capacity is to construct additional runways and associated taxiways and gates in those heavily used airports in which limited infrastructure capacity is a recurrent problem. Runway investments have the greatest potential to reduce congestion and delay in high-demand airports prone to adverse weather patterns that can severely restrict use of existing runways because of their configuration, geometry, length, and other characteristics. However, new runways are expensive to build and difficult to modify once built. The construction of new runways at major airports has proved to be a costly and time-consuming process, largely because of noise and environmental concerns, as well as the lack of sufficient land at some older, urban airports. These difficulties have prevented all but seven major airports from adding new runways during the past 10 years. The redesign of airspace and the modification of air traffic control procedures and technologies are other options being pursued by FAA for enhancing capacity at the bottlenecks. For instance, consideration is being given to increasing capacity by modifying air traffic control rules and technologies affecting approach procedures during instrument conditions. Because safety is the paramount concern, the focus of air traffic control is on separating aircraft in time and space.6 These traffic spacings— which are designed to reduce the adverse safety effects of wakes in good and bad weather—are more often applied during inclement weather, when air traffic controllers do not give pilots visual clearances. As a practical matter, the spacings tend to reduce runway capacity at some busy airports. Inclement weather can also limit the simultaneous use of parallel runways, which can substantially reduce operational capacity at some major airports. Certain improvements in air traffic control technologies and procedures are being advocated because of their purported ability to increase the capacity of terminal airspace 5 FAA’s Airport Capacity Benchmarking and National Choke Points initiatives are both examples of the agency’s intentions to enhance capacity through targeted improvements in airports and air traffic control operations. 6 Traffic in terminal airspace, where aircraft are moving more slowly, must be separated from other aircraft by at least 3 miles and 1,000 feet. The specific separation minima depend on the type of aircraft in the queue, considering aircraft design, performance characteristics, and weight. For instance, to protect smaller and slower planes from wake turbulence and because of different runway occupancy times, the in-trail arrival separations between small and large aircraft must be greater than those for two large aircraft with comparable characteristics.
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 Figure 3-4 Capacity benchmarks for 31 largest U.S. airports. (Source: FAA 2001.)
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 and airports under optimal and reduced visibility without impairing safety. These include Automatic Dependent Surveillance-Broadcast (ADS-B, mentioned in Chapter 2) coupled with cockpit displays of traffic information, which can help the pilot maintain desired separation more precisely; tools that assist the controller in better assigning runways and sequencing aircraft; and radar systems that permit simultaneous instrument approaches on parallel runways. Such changes offer the potential for only incremental improvements in capacity at most airports and terminal areas. Nevertheless, FAA believes they could increase capacity by 10 percent or more in several important airports with significant delay problems, such as Newark, La Guardia, and Philadelphia (FAA 2001). Finally, despite overall growth in traffic, the airspace system often has excess capacity during much of the day. Volume-related congestion and delays at airports tend to occur during the most convenient arrival and departure times. La Guardia, for instance, is heavily used by business travelers, who tend to prefer flights arriving and departing during the most convenient morning and evening hours. To increase travel flexibility, they also prefer departure and arrival options at frequent intervals during these peaks. Airlines, competing with one another for high-fare business travelers, have learned to schedule flights at close intervals at La Guardia, often using smaller jets (such as 60-seat regional jets) because they are economical for such service. The tendency to increase schedule density at peak times, however, has exacerbated congestion at this capacity-constrained airport, which is the most delay-ridden in the country (see Figure 3-1). Similar problems occur in San Francisco, Boston, Philadelphia, and other business markets. Thus, it is clear that an understanding of the nature of the demand for air travel is necessary to address the factors that contribute to congestion and delay. Demand management techniques to smooth the peaks and valleys in use are increasingly being considered as options for relieving chronic congestion at high-demand airports with limited capacity. Though they may not be practical or politically feasible today, the use of congestion-based landing fees and other economic incentives may become more acceptable over time to relieve congestion and reduce costs resulting from travel delay. Relevant Findings Recurrent delays in airline flights have prompted much debate about how to alleviate this problem and make air travel more reliable and convenient for passengers. Sharp growth in demand for air travel has contributed to congestion and to the flight delays and schedule disruptions that ensue. Because more people are flying, more are affected by canceled, delayed, and diverted flights. It is important to recognize, however, that most large commercial airports and nearly all smaller airports are not congested and have much idle capacity. Sustained growth in passenger traffic can be accommodated throughout much of the system. Ameliorating congestion that occurs repeatedly at particular airports is critical to alleviating flight delays that propagate widely. Improvements in airport runways, air traffic control procedures and technologies, and demand management techniques are the most likely remedies for congestion problems at these bottlenecks. Such improvements would have positive effects on the incidence and severity of delays
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 throughout the system. Congestion, however, is not the source of all flight delays and schedule disruptions. Many of the delays experienced by travelers are caused by airline practices, equipment problems, labor actions, and other factors, including severe weather, and are unrelated or only indirectly linked to traffic volume. SMALL-COMMUNITY ACCESS TO AIR TRANSPORTATION Ever since the emergence of aviation as a mode of intercity transportation during the 1930s, rural and small communities located far from major urban airports have expressed concern about having limited access to air transportation and the benefits that such service can confer. To address these concerns, the federal, state, and local governments have taken steps to foster air service in small communities, whether through subsidization of scheduled airline service or the provision of aid for improvements in small-airport infrastructure. Early in the development of commercial aviation after World War II, it was widely believed that subsidies were necessary for air service to be extended to communities too small to generate sufficient traffic volumes to attract airlines. Accordingly, the federal government, which then regulated airline fares and service areas, approved the establishment of several local-service airlines (e.g., Piedmont, Ozark, Frontier) to provide supplemental service between small communities and large airports served by the mainline carriers. The local carriers used revenues generated on their most profitable feeder routes, to which they were given exclusive rights, to cross-subsidize required service on low-volume routes. The regulated carriers, however, often scheduled flights in the smallest markets at inconvenient times and intervals so they could use the equipment on profitable routes during the peak periods (Meyer and Oster 1984). On the eve of airline deregulation in 1978, about 150 communities were receiving service from local-service carriers, often by jet airliners, as required by federal regulators. Once deregulated and given the freedom to adjust their route systems and compete with larger airlines, most local-service carriers moved their larger jet aircraft to mainline routes and abandoned the unprofitable smaller markets. Regional and commuter airlines, however, quickly filled most of the service vacancies by using lower-cost turboprop airplanes. Within a few years after deregulation, more than 100 regional and commuter airlines, most nonexistent a decade earlier, were offering scheduled air service in hundreds of small, medium, and large airports. Moreover, Congress, concerned about the potential withdrawal of airline service from small communities, established the Essential Air Service (EAS) program in the wake of deregulation. More than 100 small communities located farther than 75 miles from a larger commercial-service airport were eligible for the program, which provided federal subsidies to commuter airlines to provide minimum levels of scheduled service. Small-Community Service Today The EAS program continues today; about 80 airports receive subsidized scheduled service. Altogether, commuter airlines serve more than 500 airports across the country, most of which receive no public subsidy. As explained in Chapter 2, most of the more than 500 commercial-service airports in the United States are served primarily by commuter airlines that operate a mix of turboprops and regional jets. In the
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 Accident Occurrences The most recent detailed compilations of NTSB aviation accident investigations is for 1997. A large majority of GA accidents that year (as in all previous years) involved single-engine piston airplanes, which accounted for three-quarters of all GA accidents. These aircraft, which also comprise a majority of the GA fleet, averaged 8.1 accidents per 100,000 flight hours, which was the highest among all fixed-wing aircraft. Turboprop and turbofan jet airplanes averaged 4.5 and 1.1 accidents per 100,000 flight hours, respectively. Rotorcraft had the highest accident rates, in part because these aircraft have the shortest flights and the highest ratio of landings and takeoffs (when many accidents occur) per hour flown. About 60 percent of all accidents and two-thirds of fatal accidents involved aircraft used for personal flying. Instructional flights accounted for about 15 percent of accidents, followed by aerial applications (such as crop dusting), which accounted for 6 percent. About 4 percent of accidents involved business-related flying, excluding corporate flights. Private aircraft used for corporate transportation, which are almost always operated by professional flight crews, accounted for fewer than 1 percent of GA accidents, and their accident rates were 10 to 20 times lower than those of GA as a whole. Altogether, student and private pilots accounted for more than half of all accidents in 1997. Commercial pilots flying GA aircraft, who log many more flight hours than private pilots, accounted for about 45 percent of accidents. Accident Causes and Contributing Factors For the 5-year period 1993 to 1997—the most recent period for which NTSB has published detailed time-series data—NTSB cited probable causes and contributing factors in more than 9,700 GA accidents, including 1,885 with fatalities. Such determinations, as NTSB notes, require many assumptions and judgments, since the events leading up to an accident are often difficult to reconstruct. Because pilot decisions affect the course and severity of most aviation accidents, pilot performance is frequently cited as an accident cause or a contributing factor. Indeed, NTSB cited pilot performance as a causal or contributing factor in 82 percent of all GA accidents from 1993 to 1997. By comparison, the environment and aircraft were cited as factors in 45 and 40 percent of GA accidents, respectively. Weather is the most significant environmental factor contributing to GA accidents, although it is seldom cited as a “cause,” under the presumption that pilots are trained to make safe decisions when operating in inclement weather. In 1997, weather was a contributing factor in 20 percent of all GA accidents investigated by NTSB, including nearly one-quarter of fatal accidents. Fog and low ceilings were the most commonly cited adverse weather conditions. Through its Safer Sky Program, FAA is working to identify and address the highest-priority accident causes such as runway incursions, controlled flight into terrain, weather, and uncontained engine failures. The idea is to use NTSB reports and other accident and incident data more systematically to identify the more common accident problems, causes, and precursors in order to determine how best to allocate agency safety resources.11 11 See the FAA website for more information on this initiative (www.faa.gov/apa/safer_skies).
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 Air Carrier Safety NTSB compiles accident investigation records for air carriers according to type of service: large carriers, scheduled commuter airlines, and air taxis.12 Over the past dozen years, large carriers have had the lowest accident rates, which have ranged from 0.15 to 0.40 per 100,000 hours flown, while the fatal accident rate has ranged from 0.02 to 0.10.13 Because many commuter airlines are affiliated with major airlines and use some of the same kinds of equipment, their accident records have recently been grouped with those of larger airlines, making it difficult to distinguish any differences in accident patterns or trends. In general, however, air taxis, which provide unscheduled air service using smaller GA aircraft, have the highest accident rates among certificated air carriers. Between 1989 and 2000, air taxis had 80 to 160 accidents per year; the number involving fatalities ranged between 38 and 83 per year. Over this span, the air taxi industry has averaged about 3.8 accidents per 100,000 hours flown, including 1.0 fatal accidents. Accident rates for air taxis, therefore, have been about half of those for GA as a whole but higher than those of corporate aviation (see Figure 3-7). It is important to note that many air taxis (unlike corporate aircraft) operate in Alaska, which has an operating environment (e.g., terrain, weather, landing facilities) that is much more challenging than elsewhere in the country; hence, about one-third of all air taxi accidents occur in Alaska. In a compilation of air carrier accidents spanning 1986 to 1996, NTSB cited airline pilot performance as a causal or contributing factor in 32 percent of the 287 large-carrier accidents. The performance of other persons outside the aircraft (such as maintenance workers and air traffic control personnel) was the most frequently attributed factor, cited in 42 percent of accidents; weather conditions were attributed in 30 percent of accidents. The pilot was cited as a factor in a much higher share of air taxi accidents during the period—75 percent of the more than 1,000 air taxi accidents investigated. Challenges and Relevant Findings Individual aviation accidents can significantly affect the public’s overall perception of aviation safety. As air travel has grown over the past 40 years, both the rate and the number of civil aviation accidents have declined, tending to raise public confidence in aviation for transportation. Accident rates have declined for both commercial aviation and GA, although rates for the former remain much lower. The experience in both sectors is that professionally piloted aircraft used in transportation, often turbine aircraft, have far lower accident rates than aircraft flown by private pilots. Pilot performance is a more significant factor in GA accidents than in commercial airline accidents. Whereas crew factors generally appear in a minority (though still large percentage) of airline accidents, they account for a large majority of GA and air taxi accidents. It is noteworthy that airline and corporate aircraft, which have the lowest accident rates, are typically two-pilot operations, unlike most GA and air 12 The “large carrier” grouping includes major passenger and cargo airlines with scheduled service, as well as any other carriers using large aircraft for scheduled and charter passenger or cargo service. 13 The data referred to in this section are from NTSB’s review of aircraft accident data for 1996 (NTSB 1999) and NTSB online data reports (www.ntsb.gov).
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 Figure 3-7 Accident trends by segments of aviation industry, 1989–2000. Note: flight hours are estimated by FAA. Accident rates based on departures are not available because of limited data on GA departures. [Sources: NTSB 1999; NTSB 2000; NTSB online Tables 9 and 10 (www.ntsb.gov/aviation); NBAA 2000.]
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 taxi operations. Progress in improving GA pilot performance, though not necessarily to the extent of equaling the safety record of two-pilot professional crews, continues to be an important safety need in the GA sector. ENVIRONMENTAL COMPATIBILITY Airports have long been a focus of environmental concern. Because of their size, functional requirements, and use in transporting passengers and high-value cargo, airports tend to be located on large, flat sites near populated areas. Suitable sites are often found on the shores of rivers, lakes, and oceans, or in wetlands or other types of landscape thought to have little economic value when originally selected for airport development. These sites, however, often support important ecological systems whose disturbance can affect plant and animal communities and humans. With passage of the National Environmental Policy Act (NEPA) and similar state environmental laws during the 1970s and 1980s, airport planning and development projects became subject to much greater scrutiny by the U.S. Environmental Protection Agency (EPA), other federal agencies (such as the U.S. Army Corps of Engineers), and state environmental agencies. FAA also established a number of programs and guidance aimed at reducing the array of environmental effects at and near airports receiving federal aid. The programs have ranged from studies to resolve land use compatibility and noise-related problems at airports to the preparation of manuals for airport personnel to use in managing wildlife hazards at airports. Likewise, many states have developed planning and impact assessment guidelines for local jurisdictions and airport authorities to lessen the environmental impacts from airport operations and construction projects. The types of environmental impacts associated with the development and operation of airports are varied. They generally fall into two categories: “footprint” and “operational” effects. Footprint effects are those resulting from the location, size, and configuration of airport facilities and may include effects on water quality (surface and subsurface), wetlands, floodplains, species habitats, and land uses (farmland, parks and recreational areas, and protected landscapes, such as coastal zones). Operational effects are those attributable to changes in the volume of aviation operations and the composition of the aircraft fleet, which may result in increases in aircraft noise and pollutant emissions, as well as other social externalities such as increased highway traffic congestion. It is generally true that operational activity at large commercial airports affects more people and larger areas than does that at smaller GA airports. Nevertheless, operational effects are not negligible in many GA airports. For instance, in some locations even a modest increase in the number of nighttime operations at a GA airport—an increase that would barely be noticed at a large airport—may be perceived negatively by neighboring residents, generating significant public opposition and even legal challenges. Moreover, the severity of an airport’s environmental footprint can have little relation to airport size, since location is a critical factor. For instance, a 1,000-foot runway extension at a GA airport situated near wetlands can engender more environmental scrutiny than the construction of a new runway at a much larger hub. As commercial aviation activity has increased dramatically, so has concern about the environmental impacts associated with airport footprints and operational
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 activity. Community opposition to new airport development projects on environmental grounds has escalated in recent decades, often becoming a significant factor in delaying or preventing project implementation. Among operational impacts, aircraft noise during takeoff and arrival has historically been by far the most prominent concern. However, local air quality, which is affected by emissions from aircraft and surface traffic activity at and near airports, is growing in importance. On a larger scale, the effects of aircraft emissions on regional air quality, and potentially on global climate change and stratospheric ozone depletion, have received more attention during the past two decades. Footprint impacts also constrain airport development because of such concerns as the filling of wetlands (subject to the review and approval of the Corps of Engineers), impairment of water quality in surface and underground sources resulting from the use of hazardous substances at airports, and adverse effects on the habitats of species protected and given other special status by federal and state statutes. Aircraft Noise As airport activity increased and larger jets began operating in the nation’s urban airports during the 1960s, the communities near airports became increasingly effective in conveying their concerns about noise. Organized reactions by neighborhoods have led to strong political pressure to control aircraft noise. Heavier aircraft have tended to attract the most concern because they require more thrust during takeoff and create proportionally more noise and vibration than smaller aircraft, unless treated. Likewise, the operation of helicopters, which can have a distinctive noise profile caused in part by blade “slapping,” has proved particularly problematic. They often fly lower and slower than fixed-wing aircraft and can land and take off outside large airports; hence, their noise effects can be more intrusive and longer-lasting. Aircraft noise is surely an annoyance, but one that is difficult to measure since noise characteristics vary by source and people differ in their tolerance and reaction. NEPA requires an environmental impact assessment when federal action, such as funding aid or airport layout approval, is associated with an airport improvement or other change.14 Because most U.S. airports receive federal aid or require federal action in connection with airport development programs, they must undertake such assessments, and noise is one of the factors they must consider. EPA, which enforces and sets standards for NEPA compliance, has established methods for measuring and analyzing noise in and around airports. Airport noise exposure, expressed in terms of the day-night annual average noise level (DNL), is calculated on the basis of cumulative noise levels over the course of the day and the intensity and duration of each noise event. FAA uses a DNL value of 65 decibels as a threshold of noise impact significance for sensitive land uses (e.g., residential areas) under ordinary circumstances.15 To limit the unacceptable noise footprints, many airports have paid large sums for noise mitigation. Measures include the soundproofing of nearby homes and the purchase of land on the perimeter of the airports, which sometimes requires the relocation of households. Some airports have purchased easements from homeowners 14 State laws may require similar or additional environmental assessments. 15 According to FAA rules, 60 decibels may be used under some circumstances as a screening threshold.
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 to ensure that residents will not object to increases in airport activity. Most airports want to avoid curfews and limits on airport use. Many airport operators, however, have had to make changes to limit objectionable noise; for instance, by requiring aircraft operators to throttle back engines during climb out, limiting flight paths, and rotating runways in use. Such restrictions can affect the airport’s capacity to handle traffic, especially during inclement weather. Aircraft noise is a worldwide concern, as evidenced by the fact that the International Civil Aviation Organization (ICAO) is charged with recommending aircraft noise exposure standards worldwide. FAA has adopted ICAO standards requiring the phasing out of noisier jet aircraft and their replacement by quieter so-called Stage III aircraft. In general, newer aircraft are better designed to suppress or reduce engine noise. Still, noise concerns continue to constrain airport use and expansion in the United States and abroad. Although technology has helped reduce the maximum noise of single events, growth in aircraft traffic activity has often led to increases in the frequency, duration, and level of noise and to the expansion of noise exposure areas. It has become increasingly clear that standard noise metrics may not be accepted as measures for all aspects of community concern and that controversies about how noise is evaluated are likely to continue. For instance, intermittent or startling sounds can create community concerns, and it is well known that residents complain about aircraft movements they can see, even if they cannot hear them. It appears that even when noise is measurably reduced or contained, the sight of aircraft can provoke public outcry, partly out of concern about the risk of overflying aircraft crashing into residential areas (NSTC 1999, 51–60). Moreover, automobile traffic in the vicinity of airports, much of it generated by airport operations, may add to aircraft noise to create cumulative noise impact issues. Other Local Environmental Effects The federal Clean Air Act (CAA) requires EPA to identify National Ambient Air Quality Standards to protect public health and welfare. Standards have been established for various air pollutants including ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, suspended particulate matter, and lead. These substances are called “criteria” pollutants because standards have been established for each of them to meet specific public health and welfare criteria set forth in the CAA. (States have adopted their own ambient air quality standards, which may be more stringent, for the criteria air pollutants.) EPA has classified air basins or portions of air basins as either “attainment” or “nonattainment” for each criteria air pollutant on the basis of whether the criteria standards have been achieved. In nonattainment areas, CAA requires states to develop plans defining strategies for achieving attainment; these plans are referred to as state implementation plans (SIPs). Many of the metropolitan areas of the United States are located in air basins designated as nonattainment for one or more criteria pollutants. Within urban air basins designated as nonattainment, airports are significant sources of criteria pollutant emissions, from both stationary sources (fuel storage and distribution systems, boilers) and mobile sources (aircraft, on-road vehicles, ground support equipment). Consequently, increases in emissions associated with growth in aviation activity are
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 a concern to the regulatory agencies responsible for monitoring and improving air quality and to the general public. For this reason, development projects at major air carrier airports are typically subject to detailed analyses of how development-related increases in air passenger and cargo activity affect air quality. Moreover, airport development projects that require action by FAA, such as approval of funding or airport layout plans, must be in conformity with the applicable SIPs before FAA can approve the project. In general, if modest increases in criteria pollutant emissions are anticipated from an airport project requiring federal action or approval and FAA determines that the applicable thresholds for particular pollutants would be exceeded, additional analysis or mitigation may be required to secure acceptance. For instance, it may be necessary to offset projected increases in emissions through reductions in airport-related emissions or the purchase of emissions “credits” from nonairport sources (e.g., local stationary sources). Because identifying acceptable and cost-effective mitigations is often difficult, even the finding of modest increases in criteria pollutants from an airport project can seriously delay or preclude its implementation. Air quality concerns are also changing as more is learned about the generation and effects of pollutants. Public health agencies in recent years have increasingly focused on air pollutants known to have short-term (acute) or long-term (chronic or carcinogenic) adverse human health effects but for which no ambient standards have been established. Examples are formaldehyde, benzene, and xylene. Their emissions at airports are generated from the combustion of fuel in the engines of aircraft, on-road vehicles, and ground support equipment, among other sources. While many scientific uncertainties remain about the generation and dispersion of these substances, particularly from aircraft and other nonroad mobile sources, some states require their examination as part of the environmental documentation needed for airport development approvals.16 Air quality concerns can be significant issues for development and activity changes even at small GA airports, depending on their location and the nature of the planned changes. Even a relatively minor change that requires federal action (or in some cases, state action), such as modifications to the airport’s layout, can trigger the need for air quality impact evaluations and other environmental assessments. Although smaller aircraft generate smaller amounts of pollutants than larger aircraft per operation, increases in total aircraft operations and changes in the types of aircraft using an airport—for instance, a shift from piston-engine to turbine-engine aircraft— can change the airport’s emissions profile. Such changes may be subject to assessment and action by public agencies. This process can generate public scrutiny and perhaps challenges from nearby residents concerned about health risks from air pollutants and suspicious of possible changes in the activity patterns at the airport. An improvement in air quality at a larger airport resulting from the diversion of air traffic to an expanded smaller GA airport may not be perceived as a net air quality benefit. The 16 For example, the California state environmental documentation for the proposed expansion of Los Angeles International Airport includes an analysis of hazardous air pollutant emissions and a health risk assessment to determine whether exposure to the emissions generated by the expansion could increase the incidence of cancer or other illnesses.
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 deterioration in air quality near the GA airport may be proportionately much greater than the improvement at the larger commercial airport. Global Environmental Concerns and Energy Use Aircraft in flight have environmental effects. They can contribute to the buildup of greenhouse gases and particulate matter in the atmosphere, which can affect the earth’s radiative balance and contribute to the buildup of gases in the stratosphere that can deplete the earth’s protective ozone layer. Like other transportation vehicles that burn fossil fuel, aircraft produce carbon dioxide, which is the most plentiful and lasting of the greenhouse gases that threaten to cause a change in the earth’s climate. Aircraft flying in the troposphere also emit aerosols (microscopic airborne particles) and water vapor that can create cirrus clouds, which reflect incoming solar radiation and can have a cooling effect on surface temperatures (World Meteorological Organization 1995). The emission of oxides of nitrogen and other substances from aircraft flying at high altitudes (40,000 feet above sea level or higher) may destroy ozone in the stratosphere, which is naturally present and is an important protection against ultraviolet light penetration (Intergovernmental Panel on Climate Change 1996). Federal and ICAO regulations governing large aircraft set standards for the emission of certain substances (criteria air pollutants) during landing and takeoff cycles. There are no U.S. or international standards governing the exhaust emissions of aircraft at cruising altitudes, partly because of insufficient scientific information on which to base such standards. However, the scientific and aviation communities have begun to take seriously the atmospheric effects of aircraft emissions. Changes in the types of aircraft and where they fly in the atmosphere—for instance, an increase in the number of aircraft entering the upper troposphere and lower stratosphere—are of interest to scientists evaluating the current and prospective atmospheric effects of aviation. The risk of global environmental effects related to the combustion of fossil fuel is one reason to seek improvements in the energy efficiency of aviation. A more immediate reason for improving energy efficiency is that fuel is a major cost item for airlines and other aircraft operators. Aircraft fuel efficiency is extremely important to air carriers and private jet operators, since it is often second only to labor as an operating cost. Many older aircraft, such as the Boeing 727 and DC-9, have been retired in recent years in favor of more fuel-efficient, later-model versions of aircraft such as the Boeing 737. The airline industry has made great strides in improving energy performance, and fuel use per passenger mile has been cut in half since 1970. Airlines continue to seek changes in operating practices, especially air traffic routings and control procedures that will produce additional savings in fuel consumption. At the same time, the conversion to turbine aircraft in the business aviation and commuter airline industries has had implications for fuel usage, since turbine aircraft use several times more fuel per operating hour than do piston-engine aircraft. On a passenger-mile basis, however, the faster turbine aircraft, which travel farther per hour flown, are a fuel-efficient means of transporting people over long distances. Because takeoff and low-altitude operations use a disproportionate share of jet fuel, turbine aircraft are most energy-efficient (on a passenger-mile basis) on longer flights, during which cruising altitudes are maintained for a larger portion of the flight. In
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 addition, for the same level of turbine engine and aircraft technologies, small aircraft are inherently less fuel-efficient on a passenger-mile basis than are larger aircraft. Challenges and Relevant Findings Environmental issues impose a fundamental limitation on growth in the aviation sector. Aircraft noise will likely continue to be a major impediment to the expanded use of many airports, despite technologies that have made aircraft quieter. Increases in operations, even by quieter aircraft, continue to prompt concern by neighboring communities. Public and regulatory agency concerns about pollutant emissions have increased in recent years, and air quality has become as significant an environmental issue at many airports as aircraft noise. Other environmental effects also pose constraints on aviation: the effects of aircraft and airport operations on local water quality, special-status species habitats, and sensitive land uses. Aircraft emissions in the atmosphere that could result in far-reaching environmental effects are likely to be a source of increasing scientific and public concern. These effects are being addressed through regulation and research in varying degrees. Changes in the nature, location, and magnitude of aviation activity will undoubtedly lead to new understanding of and concerns about the global environmental effects of aviation. FINDINGS RELEVANT FOR ANALYZING SATS The following chapter findings are relevant for examining the SATS concept. They are referred to again in the assessment of the rationale and justification for SATS given in Chapter 4. Alleviating Air Transportation Congestion and Delay Future growth in air travel demand could exacerbate congestion and increase the incidence and severity of flight delays. Much of the delay experienced by passengers is attributable to bottlenecks in the system, which often result from capacity shortages at a small number of large airports with limited infrastructure and heavy passenger demand. Most commercial airports in the United States have excess capacity, even during peak travel times. General efforts to curb overall growth in passenger traffic—for instance, through diversion of travelers to other modes—hold limited potential to alleviate delay problems. While it is important to develop systemwide strategies to enhance airport and air traffic capacity, remedies that are targeted to removing system bottlenecks are essential. Small-Community Access to Air Transportation Hundreds of small cities and remote rural communities receive scheduled air service from commuter airlines affiliated with major airlines. Travelers in these small markets gain from being linked to major airline hub-and-spoke networks that create thousands of city-pair markets. Not all small and remote communities, however, have scheduled service at their local airports; travelers in these communities often must drive to other airports in the region for access to scheduled service. Airlines have learned to balance the traveling public’s preference for convenient and accessible local air service with the desire for frequent flights, faster and more comfortable aircraft,
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 and ample amenities and services at airports. By concentrating passenger traffic in a regional airport, airlines can schedule more frequent flights on larger aircraft and offer lower fares. Spreading passenger traffic over many small airports in a region raises the prospect of no single airport generating passenger volumes sufficient to support frequent flights or minimum facilities and services. Aviation Safety Aircraft accidents, especially by air carriers, are often high-profile events, affecting the public’s overall perceptions of aviation safety. Government and industry, recognizing that even small degradations can cause a loss of public confidence in flying, have gone to great lengths to ensure safety. FAA’s central mission in regulating aviation and providing air traffic control service is to ensure safety. Commercial airline transportation, which is subject to the most comprehensive government interventions, has performed with high levels of safety—several times higher than the safety performance of GA. Pilot performance tends to be a more significant factor in GA accidents than it is in commercial airline accidents. Improved pilot performance continues to be a key safety need in GA. Environmental Compatibility Environmental issues constrain growth in the aviation sector. Aircraft noise and, increasingly, air quality concerns are major impediments to the expanded use of many airports, despite technologies that have made aircraft engines quieter and reduced pollutant emissions. Growth in the overall number of aircraft operations has been associated with increases in cumulative noise and air pollutant levels. Changes in an airport’s infrastructure and use characteristics, including changes in the mix of aircraft using the airport, are therefore likely to continue to attract scrutiny, and the issues raised will require remediation. REFERENCES Abbreviations DOT U.S. Department of Transportation FAA Federal Aviation Administration NBAA National Business Aviation Association NSTC National Science and Technology Council NTSB National Transportation Safety Board DOT. 2000. Audit Report: Air Carrier Flight Delays and Cancellations. Report CR-2000-112. Office of Inspector General, Washington, D.C., July. FAA. 1999. Terminal Area Forecast Summary, FY 1999 to 2015. Office of Aviation Policy and Plans, Washington, D.C., Nov. FAA. 2000a. 2000 Aviation Capacity Enhancement Plan. U.S. Department of Transportation, Washington, D.C. FAA. 2000b. Long Range Aerospace Forecasts, FY 2015, 2020, and 2025. Office of Aviation Policy and Plans, Washington, D.C., June. FAA. 2001. Airport Capacity Benchmark Report 2000. U.S. Department of Transportation, Washington, D.C.
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Future Flight: A Review of the Small Aircraft Transportation System Concept - Special Report 263 Gaguin, D. A., and M. S. Littman. 1999. County and City Extra: Annual Metro, City, and County Data Book, 8th ed. Bernan Press, Washington, D.C. Intergovernmental Panel on Climate Change. 1996. Climate Change 1995: The Science of Climate Change. Contribution of Working Group II to the Second Assessment Report. Scientific Assessment of the Atmospheric Effects of Stratospheric Aircraft, Reference Publication 1381. Washington, D.C. Meyer, J. R., and C. V. Oster. 1984. Deregulation and the New Airline Entrepreneurs. MIT Press, Cambridge, Mass. NBAA. 2000. Business Aviation Factbook 2000. Washington, D.C. NSTC. 1999. National Research and Development Plan for Aviation Safety, Security, Efficiency, and Environmental Compatibility. Committee on Technology, Executive Office of the President of the United States, Washington, D.C., Nov. NTSB. 1999. Annual Review of Aircraft Accident Data, U.S. Air Carrier Operations, Calendar Year 1996. Report NTSB/ARC-99/01. Washington, D.C., July. NTSB. 2000. Annual Review of Aircraft Accident Data, U.S. General Aviation, Calendar Year 1997. Report NTSB/ARG-00/01. Washington, D.C., Sept. World Meteorological Organization. 1995. Scientific Assessment of Ozone Depletion: 1994. Report 37. Global Ozone Research and Monitoring Project, Geneva, Switzerland.
Representative terms from entire chapter: