10.4. Mitigation Measures

Aviation is a technologically intensive industry, both as a user and as a driver of advanced technology. Until quite recently, business units within the air service industry were often characterized as a series of local monopolies connected by a set of protected routes, which contributed to economic and environmental inefficiencies. Continued aviation liberalization has not brought decreased regulation in the areas of safety, security, and the environment however, and continued cooperation among national authorities is necessary to ensure that such regulations are globally and competitively neutral.

10.4.1. Underlying Trends Relevant to Mitigation

The general trend in aircraft engine technology development over the past few decades has been to reduce specific fuel consumption (SFC). This trend has resulted in lower emissions of carbon dioxide CO2) and water vapor (H2O) and most other exhaust gases per unit of thrust. Advances in combustor technology have resulted in considerable reduction of NOx emissions at a given pressure ratio. Future developments in engine technology are discussed in Chapter 7.

Developments in communication, navigation, and surveillance technology, as well as air traffic management systems (see Chapter 8), have enabled more efficient use of the air traffic system. This trend has resulted in considerable fuel savings. The complete transformation-that is, modernization of the air traffic system-is expected to generate significant safety, operational, and environmental benefits. Air traffic measures for present and future systems offer potential for reduced fuel consumption, hence emissions, through improvement in the overall capacity and efficiency of the air traffic system. Potential environmental benefits to be gained from operational measures within the current air traffic system, though important, are thought to be smaller than those that may be gained through modernization of the air traffic system. The environmental effect will depend on the rate at which these measures are adopted.

Chapter 9 examines the implications of alternative growth and technology scenarios on aviation emissions. Mid-term projections of aviation growth have meaningful margins of error, and those beyond 20 years are highly uncertain. Accordingly, rather than use projections, we develop a range of future industry growth and technology scenarios to the year 2050. Comparison of scenarios gives order-of-magnitude estimates of emissions changes resulting from variation in the rate of aviation growth and different technology options. Although these scenarios produce a wide range of outcomes, they all show an increase in aircraft emissions as growth outpaces engine technology improvements.

The scenarios assume minimal fuel consumption resulting from the use of optimal fight paths and absence of delay. Unlimited development of the aviation infrastructure projects unconstrained growth of aviation. Chapter 8 addresses current policies, which are expected to diminish the environmental effects of additional fuel consumption resulting from present air traffic management technology and systems. Unconstrained growth-an assumption that is not representative of conditions today or in the future-thereby becomes the dominant factor. Because the scenarios assume complete modernization of the air traffic system and no infrastructure constraints, growth of traffic and emissions are thought to be overstated in the modeling exercises.

10.4.1.1. Deregulation and Subsidies

An important factor for promoting the sustainable development of aviation is ensuring that producers and consumers receive appropriate signals about pollution costs and natural resource scarcities. The focus of aviation policy over the past 15 years has begun to shift from command-and-control policies to enhancing efficiency and responding to changing demand patterns. Two broad categories of issues-the operation of markets, and government supports and ownership-bear on environmental mitigation measures (OECD, 1997b).

Government regulation of competition in international aviation has restricted market entry and exit, fares, and capacity. Internationally, liberalization of bilateral air service agreements is aimed at increasing competition within "the home market" and promoting greater efficiency. Although aviation remains a quasi-protected industry in some countries, deregulation is becoming the predominant trend within national markets.

Economic deregulation of the U.S. airline industry began in 1976, and was completed in 1983 when all regulations on domestic fares, entry, and exit were eliminated. This deregulation resulted in a 33% lower fare structure and higher average industry load factors, which have increased from 52% (1960-69) to more than 70% (1995-98). Following deregulation, increases in traffic volume, fuel use, airport and air traffic congestion, and noise that some observers consider to be above "normal" have been attributed to the hub-and-spoke method of operation that ensued. Studies comparing the effect of direct versus hub-and-spoke routing on fuel consumption, traffic levels, and fleet mix have not been undertaken (Winston, 1998).

When the environmental cost of a supported activity is placed outside the market transaction, many subsidy or tax treatments are thought to have adverse environmental consequences to the extent that they generate negative effects. The most important examples of explicit government supports to aviation are nonmarket pricing of infrastructure services, below-market financing, tax and depreciation preferences for oil, and direct government ownership. These and other issues are being studied (OECD, 1997b). Lack of inclusion of environmental costs is currently thought to be an implicit subsidy to industry and consumers. All of the mitigation measures discussed below internalize or include external costs to the service provider to some degree. An important issue for further research is whether the full costs of externalities can be quantified in advance.

10.4.1.2. Cost Structure

Fuel cost and consumption are important to the mitigation measures discussed below. Examination of the historical record indicates that aviation fuel productivity has increased considerably. ICAO estimates that, while aggregate fuel consumption for the 1976-90 period grew approximately 60%, world civil air traffic (passengers, freight, and mail combined) increased about 150%. These figures are explained by an increased average load factor, a more optimal aircraft fleet mix, greater engine efficiency, and improved system capacity (Balashov and Smith, 1992). The amount of fuel consumed and fuel productivity affect airline profits and ticket prices.

Of interest to the policymaker is the effect of a change in fuel price on airline cost and fare structures and on passenger and cargo demand. Figure 10-1 shows the percentage of total annual airline expense attributable to fuel cost for U.S. and world airlines over time and compares changes in this ratio against changes in the index of fuel prices for the United States and the world. Data for the figure were extracted from industry and ICAO published sources (ICAO, 1996b; Aerospace Industries Association of America, 1998). The data indicate that average fuel cost across the industry has recently represented about 11-15% of operating costs, but has been higher during times of high fuel prices (e.g., nearly 30% in the early 1980s). Further analyses of the impact of fuel prices on demand and industry profitability are needed.

Against the background of these underlying trends, the potential role of mitigation measures is considered in further reducing the growth of aircraft emissions by forcing technology, changing industry practices, and dampening growth in traffic.

10.4.2. Regulatory Measures

Atmospheric environmental impacts associated with aviation emissions include greenhouse gas emissions, ozone depletion, acidification, and impact on local air quality. Cruise altitude (above 900 m) aircraft emissions of interest are CO2, NOx, particulates and aerosols, sulfur compounds, and H2O. Ground-level (altitude below 900 m) aircraft emissions of interest to local air quality issues are NOx, carbon moNOxide (CO), unburned hydrocarbons (HC), and other volatile organic compounds. Ground-level CO2 emissions from aircraft are of interest because of their effects on climate. This section examines more fully two technology-based means for mitigating the adverse effects of aviation emissions.

10.4.2.1. Operational Means to Reduce Emissions

The environmental aim of air traffic system modernization and operational measures is to reduce fuel consumption, hence emissions, through improvement in the overall efficiency of the air traffic system. For 1995, U.S. airlines reported a 79% "on-time" arrival rate for all domestic flights (i.e., flights arriving within 15 minutes of schedule), including canceled flights and those with mechanical delays. For 1996, this figure was 75%. This decline indicates the scope of current congestion and delay problems (U.S. Department of Transportation, 1998).

U.S. Federal Aviation Administration (FAA) data show that annual system delays of 15 minutes or longer (as a percent of total operations) have declined steadily from 2.2% in 1989 to 1.2% in 1997. Over that period, 55-70% of these delays were caused by weather; 25-35% were caused by terminal volume and closed runways and taxiways (U.S. Federal Aviation Administration, 1977). FAA estimates of the total cost for air carrier delay (operating plus passenger time costs) grew from $6.5 billion in 1987 to $9.5 billion in 1994. Except for the cost of fuel, environmental costs were not considered (U.S. Federal Aviation Administration, 1995). The European Organisation for Safety and Navigation (EUROCONTROL) reports that air traffic delays in Europe are primarily the result of national institutional factors, capacity overloads, and air traffic control inefficiencies. Association of European Airlines (AEA) data show that in 1989, the number of departures for short- and medium-term flights delayed by more than 15 minutes was 23.8%. This figure dropped to 12.7% in 1993, but has risen steadily since then: The rate was 19.5% in 1997 and 20.1% for the January-June 1998 period (Association of European Airlines, 1998). These data are consistent with EUROCONTROL data for the same years (EUROCONTROL, 1998).

ICAO air traffic system policies, plans, standards, and recommended practices have not been regarded as measures that might be used to achieve environmental gains. Studies assessing the costs and benefits of CNS/ATM modernization conclude that the benefits to airlines and passengers from reduced delays and fuel savings far outweigh the incremental costs. Recent studies have focused on estimating the environmental benefits of a more efficient air traffic system. These studies indicate that emissions from aviation may be reduced significantly. Although states are working within ICAO toward global modernization of the air traffic system, this activity has only recently been placed in the context of addressing environmental issues (EISG, 1995; Aylesworth, 1997; U.S. Federal Aviation Administration, 1998a,b).

Studies and working papers prepared for CAEP/3 Working Group 3 (emissions) and the ICAO Worldwide CNS/ATM Systems Implementation Conference (see Chapter 8) indicate that improvements to the air traffic system could reduce annual fuel consumption 6-12%. For the total flight regime, 94% of fuel saving would occur at cruise altitude and 6% below 900 m. NOx reductions are estimated to be 10-16%. This discussion of measures for mitigation leads to the following conclusions:

. Potential gains from operational measures within the current air traffic system are much smaller than those that may be gained through modernization of the air traffic system.
. Although modernizing the air traffic system and improved operational measures are important environmental policy instruments in their own right, delayed or early realization of their potential would have adverse or beneficial environmental consequences, respectively.

These conclusions have important environmental policy implications. Successful implementation of CNS/ATM is a daunting task that requires worldwide and regional collaboration and cooperation. Impediments to be overcome include restricted airspace, sovereignty issues, institutional development, and finance, particularly for developing nations and countries in transition.

10.4.2.2. Engine Emissions Stringency

ICAO Annex 16 emission standards are certification requirements for individual engines (ICAO, 1993b). Because of extensive regulation of the industry to maintain high levels of safety and to maintain and promote competition, as well as comparatively long technology development and product economic lifetimes (Chapter 7), ICAO has set limitations on emissions at their sources (stringency) on the basis of the best achievable technology by all manufacturers.

These ICAO standards define emissions levels for unburned HC, CO, NOx, and smoke. They do not address aircraft emissions of CO2, sulfur dioxide (SO2), or H2O. Neither are there any ICAO standards for trace compounds such as particulates, aerosols, certain types of HC, and other nitrogen compounds. Aviation is not a source of nitrous oxide (N2O), a greenhouse gas. ICAO Annex 16 standards are related to engine emissions during the LTO cycle; they do not specifically address engine emission levels for altitudes above 900 m (cruise), although these emissions are related to emissions during the LTO cycle.

In 1981, the ICAO Council adopted standards and recommended practices for aircraft engine emissions by establishing regulatory emissions maxima for engines manufactured after 1985. The regulatory conformance criteria for covered emissions are based on characteristic engine performance during the LTO phases of flight, which represents on average of 15% of the total flight segment. LTO cycle operating requirements are characterized by very low and very high power settings, which are not representative of aircraft performance at cruise conditions. For purposes of estimation, LTO cycle parameters are transformed into an emissions index (EI) for a given airframe-engine combination to characterize emissions under cruise conditions.

On the recommendation of CAEP/2, in 1993 the ICAO Council amended the emissions standards for NOx, reducing permitted levels by 20% at a representative engine pressure ratio of 30. The certification regime follows the LTO cycle basis established under the original stringency standard. The CAEP/2 standard was adopted by ICAO member states with few, if any, exceptions as the universally recognized international standard for aviation. It is to be applied to all engines produced after 2000, to all new and derivative engines for which certification has been or is to be applied for after 1995, and, as a practical matter, to currently certified in-production engines that are to be altered to meet the standard. CAEP has since reviewed the NOx stringency issue in light of local air quality and atmospheric concerns and in 1998 recommended that the standard be further reduced by 16% at an engine pressure ratio of 30 (ICAO, 1998a). For pressure ratios above 30, the slope of the NOx maxima was returned to that of the 1981 standard to permit greater fuel efficiency and therefore greater reductions in CO2, H2O, and oxides of sulfur (SOxO). Recognizing the need to protect the asset value of the existing fleet, the new standard is to be applied only to new or derivative engines certified after 31 December 2003. In-production engines are thereby left unaffected by the stringency requirement. The ICAO Council is scheduled to review the proposed standard and recommended practice (SARP) by the first quarter of 1999. Adoption by the Council is expected, after which the SARP will be incorporated into ICAO Annex 16 for adoption by member states. Although there is a wide range of views concerning the scale of costs and benefits resulting from increased NOx stringency, an analysis of the environmental benefits obtained to date under current ICAO engine stringency standards has not been initiated.

The three ICAO SARPs are shown in Figure 10-2 (ICAO, 1995a). It suggests that ICAO stringency requirements have "pushed" engine emissions reduction technology or, at a minimum, have ensured its incorporation into new and derivative engine designs. The relatively wide variation in technology levels among individual engine types and whole engine families represented in Figure 10-2 raises three important issues. For purposes of regulating aviation engine emissions, the first policy matter is whether use of the existing "best achievable" standard is preferable to the "best available" standard used for other industries. The second question concerns the optimal level at which the standard should be set to promote sustained and rapid progress on further emissions reduction. The third policy matter pertains to the means to evaluate tradeoffs concerning technical limitations in minimizing various emissions species and those pertaining to safety, performance, and environmental objectives, in particular noise control.

ICAO practice has inferred that the "best technology" concept has a specific meaning for aviation. The airworthiness concern is that setting standards based on unproved, anticipated, or nonexistent technology might result in untenable solutions, as might requirements that all engines meet a single, extremely low emissions threshold. A matter yet to be addressed is that selection of a "best available" technology or technology level for aircraft engines has inherent competition and market structure implications. Accordingly, as part of the work program adopted at CAEP/4, members called for looking into "establishing long-term and forward-looking CAEP goals for aircraft emission reductions" to meet the industry need for extended planning horizons while more aggressively "pushing" technology development (ICAO, 1998a).

ICAO certification standards are being regarded as a means for reducing overall emissions levels. Since CAEP/4, work has begun on developing parameters for aircraft emissions certification during climb and cruise phases of flight (above 900 m) to complement the existing LTO-based standard.

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