The 11-level Geophysical Fluid Dynamics Laboratory global chemical transport model (GCTM), which explicitly treats NOx, HNO3, and PAN as transported species, has been used to assess the impact of sub-sonic aircraft emissions on the distribution of reactive nitrogen compounds (NOy) in the atmosphere. A three-dimensional aircraft source inventory compiled by Boeing and McDonnell Douglas [Wuebbles et al., 1993> has been used, in conjunction with previously compiled surface-based fossil-fuel combustion and stratospheric source inventories. Consistent with previous two-dimensional model calculations, we find that aircraft emissions have a significant impact on upper tropospheric NOx and HNO3 budgets in the mid- and high latitudes of the Northern Hemisphere. Moreover, we find that the relative impact of the aircraft source on upper tropospheric NOx levels at mid- and high northern latitudes varies longitudinally, and that in certain regions the aircraft source dominates the total NOx budget. Aircraft emissions appear to only minimally impact the NOy budget in the Northern Hemisphere lower troposphere, and in much of the Southern Hemisphere. In contrast to a previous study with a simplified transport model [Ehhalt et al., 1992>, we find that it is not necessary to invoke fast upward transport of surface emissions to explain the STRATOZ III measurements of NO in the upper troposphere of Northern Hemisphere mid-latitudes in the GCTM. However, comparisons of model results with NOy measurements at Mauna Loa, Hawaii, and over western Alaska suggest that sources other than surface-based fossil-fuel combustion, stratospheric NOx production, and aircraft emissions, are significant in determining the free tropospheric NOy budget in these regions. ¿ American Geophysical Union 1993