The historical fuel efficiency characteristics of regional aircraft from technological, operational, and cost perspectives

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2001.Includes bibliographical references (p. 95-96).The air transport industry has grown at an average annual rate of 9% worldwide since 1960 and is expected to experience 5% annual growth worldwide for the foreseeable future. Recently, this rapid growth has fueled concern about the contribution of aviation activities to global climate change. Governments, airlines and manufacturers are currently debating the feasibility and effectiveness of various strategies aimed at mitigating the environmental impact of aircraft emissions. Policy responses including the implementation of taxes, emissions trading schemes, environmental charges and voluntary agreements between airlines and governments are all being considered. In order to design effective approaches towards emissions reduction, there is a need to understand the mechanisms that have enabled historical improvements in aircraft efficiency. This thesis focuses on the impact regional aircraft have had on the efficiency of the U.S. aviation system, and examines how the technological, operational and cost characteristics of turboprop and regional jet aircraft have influenced the fuel efficiency of the regional aircraft fleet. These characteristics have been compared to larger narrow and wide body aircraft, providing two different perspectives on technology evolution, airline operations and the impact of costs on both. Regional aircraft are playing an increasingly important role in the evolution of U.S. airline operations. In particular, the widespread adoption of the regional jet is transforming the aviation landscape by expanding hub operations, replacing larger jets in low-density markets, replacing turboprops in shorthaul markets, and opening up new hub-bypass routes. The impact of this transformation on congestion and aircraft emission issues is not yet obvious, but there is potential to exacerbate existing problems. Regional aircraft consume more fuel per unit of passenger travel than larger aircraft and they take up considerable space at already congested airports. Although they currently perform just under 4% of domestic revenue passenger miles in the U.S., they account for almost 7% of jet fuel use by U.S. airlines, and for 40% to 50% of departures at U.S. airports. In addition, regional traffic is expected to grow 7% to 8% annually in the U.S. during the next decade compared to 4%-6% for the major U.S. commercial airlines. Comparisons show that regional aircraft are 40%-60% less fuel efficient than their larger counterparts, while regional jets are 10%-60% less fuel efficient than turboprops. It is revealed that fuel efficiency differences can largely be explained by distinctions in aircraft operations. Aircraft flying short stage lengths spend approximately 15% more time on the ground for each hour spent in the air than longer flying aircraft, therefore consuming more fuel while taxing and maneuvering at airports. They also spend between 20% and 60% of their airborne time climbing to altitude, at associated high levels of fuel consumption, compared to approximately 10% for large aircraft. In this respect, turboprops are shown to be more efficient than regional jets because they are designed to fly at lower altitudes. As a result of these operational differences between aircraft types, large aircraft realize total energy efficiencies much closer to their optimum rate of efficiency achieved during cruise flight than regional aircraft. The total rate of fuel consumption of regional aircraft was found to be 2.7 times higher than rate of fuel consumption achieved during cruise flight. For large aircraft, the total rate of fuel consumption was only 1.6 times higher than at cruise. A similar comparison of regional aircraft revealed that the total fuel consumption of regional jets was on average more than 3.5 times as high as that achieved at cruise, while for turboprops this figure was closer to 2.3 times as high. It is also shown that regional airlines have been able to operate regional jets at higher load factors than turboprops, such that the energy consumed per unit of passenger travel for regional jets and turboprops has been comparable, even though turboprops have higher fuel efficiencies. The economic characteristics of regional aircraft were also examined. Direct operating costs per RPM are shown to be 2 -6 times higher for regional aircraft because they perform fewer miles over which to spread fixed costs incurred every time an aircraft performs a flight, regardless of distance flown. The higher operating costs of regional aircraft are consistent with the yields of regional airlines, which in 1999 were on average 2 times higher than those of large airlines.by Raffi Babikian.S.M