The potential impact of a future fleet of high-speed civil transports (HSCTs) on the year 2015 atmosphere is examined using the three-dimensional stratospheric chemical transport model, SLIMCAT. The model scenarios performed are identical to those used by the recent Intergovernmental Panel on Climate Change <1999> aircraft assessment. The importance of the background meteorological conditions in determining the potential impact of HSCTs is assessed by forcing the model with U.K. Meteorological Office analyses for the years 1992--1998. The use of annually varying meteorological analyses leads to an interannual variability in the modeled transport of aircraft-emitted NOx and H2O from the North Atlantic flight corridor. The resulting calculated O3 perturbation exhibits an interannual variability of ~50 ppbv in the middle stratosphere, which is of a magnitude similar to the differences between the O3 perturbations calculated by models within Intergovernmental Panel on Climate Change <1999>. This result highlights both the importance of the chosen background meteorological conditions in aircraft assessments and the extent to which differences in meteorology contribute to differences between model calculations. ¿ 2000 American Geophysical Union