To mitigate the environmental impact of aviation while still allowing for growth in air transportations, various organizations - such as NASA - have set goals for advancing technologies that reduce the impact of aircraft on the environment. Meeting these goals would improve the environmental performance of an individual aircraft; however, the environmental impact of air transportation is a fleet-level effect that depends on the combined operation of all aircraft with their associated technologies. Economic factors, like fuel price, also impact aviation emissions, because economic factors drive air transportation demand and drive airline fleet composition. This paper analyzes the sensitivity of environmental metrics to the entry-into-service (EIS) dates of various potential new aircraft and to the penetration rate of these new aircraft into the fleet. The studies also incorporate three potential fuel price change scenarios. The results suggest insights in two areas. First, the level of (carbon) emissions is sensitive to EIS dates of new technology aircraft only during a short period after the introduction; later EIS dates lead to airlines upgauging their fleet to maximize profit. Second, high fuel price reduces demand, which reduces emissions, especially on short routes where alternative modes of ground transport likely exist.