Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Aviation and the Global Atmosphere
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7.1. Introduction
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This chapter considers how aircraft technologies influence emissions at altitude today and how that may change in the future. This introductory section sets the scene
by briefly sketching the development and size of today's industry, outlines the approach the authors have adopted to their task, and describes the structure and content
of the rest of the chapter.
Major advances in aircraft technology have been achieved in the past 40-50 years. Over that period, principal methods of propulsion have changed: Propeller aircraft
were succeeded by jet-powered aircraft of the 1950s; these jets, in turn, were superseded by today's turbofan-powered aircraft from 1970 onwards. The fleet has
expanded rapidly. So too has the capacity of jet aircraft-rising from typical 150-seat versions of the late 1950s to the largest 525-seat variant of the 747-400 aircraft in
service today. The performance and capability of aircraft has also changed greatly. Cruise speeds of propeller aircraft have trebled from the 100 knots typical of the
1940s. At the start of the commercial jet age, speeds rose to 450 knots. Today's turbofans cruise at average speeds of around 500 knots, and the Concorde reaches
1350 knots. The search for efficient cruise performance with greater range, particularly for long-haul aircraft, has also resulted in higher flying aircraft-a key factor in
determining where most aircraft emissions occur and their resulting impact (as discussed in Chapters 2 to 6). Average cruise altitudes for propeller aircraft rose from
about 3 to 7.5 km; today's jets cruise primarily between 10.5 and 11.5 km, with some operating at up to 13 km.
● Aviation designers and regulators must address complex challenges, given the operating conditions encountered by aircraft and the correspondingly stringent
technical and airworthiness requirements that must be met. Factors that have been and will continue to be considered include the following:
● Passenger safety must be assured for all phases of aircraft operations.
● Aircraft are more severely constrained by volume and weight considerations than ground-based forms of transportation, placing more stringent limits on
available technology choices.
● Aircraft systems are typically more complex than other transport modes, and many physical and chemical effects associated with them are closely coupled and
interdependent. As such, changes in technology aimed at improving one aspect of performance, (e.g., a particular pollutant, or passenger safety) may have
adverse effects on other aspects of performance (e.g., fuel efficiency).
● Time scales for technology development and product life are on the order of decades.
● Costs to develop, purchase, and operate aircraft are high relative to many other forms of transportation (aviation costs are typically counted in millions and
billions of dollars). As with any other commercial product, the impact of technology changes on cost and customer satisfaction must be carefully assessed.
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