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Recent work has shown that when an aircraft encounters ambient ice-supersaturated conditions (where contrails may form and persist), it may be possible to avoid contrail formation by shifting cruise altitude up or down 2000 feet. If an aircraft's cruise altitude is shifted from the optimal profile during a portion of the mission, fuel consumption increases. Because on average approximately 20% of distance flown by commercial airliners is through ice-supersaturated regions, this study quantifies the fuel burn penalties for the notional scenario of flying the same fraction of cruise at altitude displacements of +2000, -2000, and -4000 ft. Present aircraft performance data was used to generate accurate fuel burn penalty estimates. This study finds that the net penalties for existing aircraft to fly contrail avoidance shifts vary between 0.2% and 0.7% increase in block fuel consumption.

The commercial airplane designer is faced with the challenge of balancing many factors to achieve an optimal airplane design, namely, how to reduce jet fuel use while also maintaining or improving emissions, noise, cruise speed, operating cost, range, reliability, maintainability, payload, takeoff field length, initial cruise altitude, and landing speed. Often, fuel efficiency improvements run counter to other design constraints imposed on the aircraft manufacturer by market forces. However, emerging engine and airframe technologies will help to continue the historical trend towards reduced fuel use. Five concept airplane designs will be reviewed that use future technology to enable the design of more environmentally friendly airplanes.