Emissions Limits
Aircraft emissions are controlled through stringent emission limits on aircraft engines. Beginning in 1973, the Environmental Protection Agency (EPA) published the first aircraft engine emission standards, limiting emissions of nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC) and smoke. In 1981, the International Civil Aviation Organization, with input from the EPA and the FAA, published the first international stringency standards limiting the emissions of NOx, CO, and HC. On March 24, 1993, the ICAO Council adopted a standard that further limited NOx emissions by 20 percent below levels established in 1981. In July 1997, the EPA adopted NOx and CO emissions standards which aligned the U.S. regulations with those adopted by ICAO in 1981 and 1993. On February 26, 1999, ICAO approved the adoption of an additional 16 percent NOx reduction standard. The EPA adopted the 1999 ICAO NOx standard into U.S. law and it became effective on December 19, 2005.
In March 2005, ICAO adopted a further 12 percent NOx reduction standard, which applies to newly-certified commercial aircraft engines after January 1, 2008. This standard currently is under consideration by the EPA. As a practical matter, however, the new ICAO international stringency standard is in effect since all engine manufacturers are building engines to the standard.
The ATA member airlines continue to support efforts to address the local air quality impacts of aviation. Nevertheless, it should also be noted that compared to other modes of transportation, commercial aviation results in significantly less overall emissions than other modes of transportation.
Tradeoffs
Emissions standards for NOx have continued to become more stringent during the past 15 years as NOx reduction technologies have improved. However, there are fundamental tradeoffs between NOx reduction, fuel efficiency, and noise reduction. For example, engines obtain the best fuel efficiency at very high temperatures, but high engine temperatures also result in an increase in NOx formation. Another example of a tradeoff is the size of the engine bypass ratio, a higher bypass ratio and lower pressure ratio generally result in a quieter engine with better fuel economy, but also generate more NOx. Therefore, aircraft engine design must currently take into account the physical tradeoffs between noise, fuel efficiency and emissions reductions.
While physical tradeoffs continue to exist, manufacturers and research organizations are investing significant resources in the development of advanced combustors which hold the promise of further reducing NOx emissions.
Infrastructure and Operational Improvements to Reduce Local Air Quality Impacts
The modernization of the air traffic management (ATM) system through FAA’s Next Generation Air Transportation System (NextGen) will allow for more direct routes and reduce delays, which will result in lower fuel burn and decreased emissions. The improved ATM system should also allow for more fuel efficient operational procedures, such as Continuous Descent Arrival (CDA). Improvements under NextGen will enable CDA procedures to occur more frequently, even during high-traffic time periods. Because of the limitations of the currently outdated, radar-based air traffic control, these beneficial operations are more difficult to employ. The modernization of ATM also will reduce congestion and optimize airport ground and terminal airspace operations, which will reduce both noise and emissions.
Ground Support Equipment
Vehicles and equipment used to service aircraft between flights are called Airport Ground Support Equipment (GSE). GSE include fuel trucks, tugs and tractors, and ground power units, among other equipment, which perform myriad complex and time-sensitive functions essential to the safe and efficient use of the National Airspace System. These functions include aircraft maintenance, fueling, deicing, starting aircraft engines, moving aircraft to and from the gate, and loading, unloading, and sorting cargo and baggage. The ability of GSE to perform all of these activities quickly, reliably, and in close coordination with each other and with the various types of aircraft in operation at various airports each day, directly affect the ability to move aircraft efficiently from the gate, through the runway queue, and into the air safely and on schedule. In short, as the FAA has confirmed, "reliable GSE equipment is . . . essential to safe and efficient use of navigable airspace.”
The type of GSE used by a particular ATA member at any given airport depends on a variety of factors including the size of the operation, the airport infrastructure, and the climate, among other considerations, with the goal of having the right equipment available to service aircraft in the most efficient manner. When purchased, each piece of GSE must meet applicable EPA air emission standards.