Aircraft Operations

Introduction

Since that first flight at Kitty Hawk in 1903, aviation has advanced at an astonishing rate to become a key component of developed economies and societies. Because of the success of aviation, aircraft operations consume increasing amounts of fuel and produce more emissions and noise. Today, the environmental impacts of aircraft, mainly engine noise and emissions, are a small but significant fraction of the total consequences of fossil fuel consumption. In the future, expected growth in the aviation sector, as well as the larger impact of some emissions when they are released at higher altitudes, will make aviation noise and emissions increasingly significant here and in other countries.

The list of contemporary and future environmental issues that aviation must address includes the following:

1. takeoff and approach noise (which present different technological problems for subsonic and supersonic aircraft)
2. flyover noise from cruise altitudes in very quiet areas
3. sonic booms and hyperbooms (i.e., the thermospherically refracted and very low intensity remains of sonic booms)
4. taxi and engine run-up noise
5. fuel venting and fuel dumping
6. emission of CO, hydrocarbons, and NOx in the airport area (below 3,000 feet)
7. contrail formation
8. emissions of CO2
9. emissions in the upper troposphere and stratosphere (from both subsonic and supersonic aircraft) of water vapor, NOx, sulfur particles, and carbon particles
10. potential for greenhouse effects and depletion of stratospheric ozone

Aviation provides significant national benefits—

1. as an engine of commerce and social interaction, transporting people and goods rapidly and safely on diverse missions all over the world
2. as a vigorous sector of the economy that provides direct economic benefits by generating jobs and exports in the design and manufacture (United States) of engines, airframes, and avionics used by airlines, airports, and associated industries

Energy Consumption and Its Consequences

The adverse environmental effects of jet aircraft are primarily a consequence of the combustion of petroleum. Jet fuel is largely carbon and hydrogen, and so combustion releases carbon dioxide (CO2). Other gases, including oxides of nitrogen (NOx), are also produced by chemical interactions with the air flowing through the engine. Water vapor emitted by the engine combines with water vapor already present in the atmosphere and sometimes freezes to form condensation trails (contrails) behind the aircraft. Under some atmospheric conditions, ice crystals in the contrails grow and disperse, increasing the amount and intensity of regional cirrus clouds and modifying the atmospheric radiation budget that controls average global temperatures. With respect to aviation noise, the internal noises of the turbine engines combine with the noise generated by the jet exhaust and the rush of air over the airframe itself.

Fuel consumption is a key indicator for assessing trends in emissions. The aviation industry is growing and the use of aviation fuel is increasing at a rate comparable to that of other uses of fossil fuels.

Recognizing that reductions in fuel consumption rates are advantageous from both economic and environmental perspectives, industry has increased the efficiency of aircraft engines and aircraft. Indeed, the amount of fuel consumed per revenue-passenger-kilometer has been considerably reduced since the advent of commercial jet transports, albeit at a slowing rate of improvement in recent years.

The situation is similar with respect to aircraft noise: aircraft performance has improved, but not as fast as demand has increased. Part 36 of the Federal Aviation Regulations covers noise requirements that aircraft must meet for FAA certification. Since it was issued in 1969, Part 36 has been amended more than 20 times and now covers virtually all types of aircraft. Several of these amendments have instituted more stringent noise requirements. On two occasions, amendments required large numbers of aircraft that could not meet new noise restrictions to be phased out of operation even though they were still flightworthy. New, stricter regulatory requirements are expected in the future as a result of ongoing action by the International Civil Aviation Organization (ICAO), which takes the lead in setting international standards that many nations, including the United States, subsequently adopt as national standards.

Because of advanced technology, the perceived noise level produced by new commercial jet aircraft of a given size has been reduced by about 10 dB since the 1960s, which is equivalent to reducing annoyance by roughly a factor of 2 (FAA, 1997). These improvements have resulted primarily from technological advances that were incorporated into more economical aircraft and propulsion systems. Despite these improvements, noise is becoming more of a problem for several reasons:

1. The amount of air traffic is growing.
2. The number of very large aircraft is increasing (for a given level of technology, one large aircraft generally produces a higher noise level than several smaller aircraft with the same total passenger capacity).
3. The hub-and-spoke routing system used by most airlines concentrates a lot of traffic and noise at a relatively small number of airports.
4. Public acceptance of noise is diminishing.

Community concerns about noise and other environmental effects result in airport curfews, flight path restrictions, and delayed or canceled airport expansions. Three-quarters of the delays experienced by expansion projects at the 50 busiest U.S. airports are primarily because of environmental issues and 12 of the 50 busiest airports have had at least one expansion project canceled or indefinitely postponed because of environmental issues (GAO, 2000).