Trends in Aircraft Efficiency and Design Parameters

Developing an aircraft CO₂ candidate metric and subsequent compliance assessment requires an understanding of practices and trends in aircraft design. Historically, fuel burn has been an important consideration for airlines, and manufacturers have responded by developing technologies to improve the efficiency of new aircraft designs. However, market forces also demand improvements in aircraft performance beyond reduced fuel burn. As a consequence, some portion of efficiency gained through improved technology has been devoted to increasing other aircraft design parameters such as range, maximum payload, and speed rather than to reducing emissions on a constant mission.

This paper investigates several important issues related to designing a representative “test cycle” for measuring aircraft efficiency under a CO₂ standard. It shows that (1) aircraft are rarely used at their maximum potential (maximum range and payload) in operation; and (2) measuring efficiency at those maximum potential points is likely to systematically overestimate real efficiency improvements in operation. By analogy, regulating aircraft efficiency at maximum range at maximum payload would be akin to setting fuel efficiency targets for cars at Autobahn speeds, with measured improvements unlikely to be reflected under real city/highway driving conditions.

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