NASA’s Subsonic Fixed Wing (SFW) Project places high importance on reducing fuel burn, nitrogen oxide (NO_X) emissions and noise exposure in future generations of aircraft. Because the amount of fuel burned is directly proportional to the amount of CO₂ emissions, reducing fuel burn will also reduce CO₂ emissions. However, the SFW goals only incorporate individual aircraft performance and do not account for how fleet-level emissions will change with the introduction of new, more efficient aircraft, which may change due to the airline’s use of the new aircraft. Furthermore, the environmental and economic impact of a new aircraft is not only a function of the aircraft’s performance but also how the airline uses the new aircraft along with other existing aircraft to satisfy passenger demand for air transportation. The allocation of existing and future aircraft models over a network of 257 airports evaluates the fleet-level impact of new aircraft by measuring fuel burn, NO_X emissions, local noise exposure, and direct operating costs (DOC) at the fleet-level. The new aircraft are incorporated into the existing fleet in ways that best achieve the objective of the allocation problem. Examining fleet-level metrics helps to determine if NASA’s SFW goals are acceptable for meeting environmental goals established by international organizations such as the International Civil Aviation Organization (ICAO) and the International Air Transport Association (IATA), or whether attaining these targets requires more ambitious goals for future and current aircraft. The studies presented here examine how fleet-level metrics evolve from 2005 to 2050 with the addition of new aircraft. Special interest is paid to the year 2030 where studies examine DOC vs. CO₂ emission tradeoffs, as well as 2050 where additional studies explore fuel burn efficiency vs. passengers served tradeoffs. The allocation approach developed and implemented here shows that, while meeting future aggressive technology development goals for individual aircraft, the total fleet emissions will continue to increase as travel demand increases, but the emissions per passenger mile will decrease. Furthermore, goals set forth by IATA become unattainable without drastic decreases in passengers served, substantial improvements in fuel burn efficiency, or a substantially different introduction of new aircraft.