The sound exposure level is calculated for a level flight. The aircraft is assumed to be a nondirectional point source and its power spectrum similar to the ``typical power spectrum'' given in Noise and Vibration Control Engineering [edited by L. L. Beranek and I. L. Ver (Wiley, New York, 1994)]. The equivalent absorption coefficient was calculated for different weather conditions, i.e., temperature and relative humidity (ANSI S1.26-1995). The ground attenuation is incorporated using the far-field approximation of the Weyl--Van der Pol solution [K. Attenborough, Appl. Acoust. 24, 289--319 (1988)] and the dependence upon the grazing angle [Lee et al., J. Sound Vib. 145, 111--128 (1991)]. The free parameters of the model can be found by measurements of the sound exposure level. The model has been developed as much for its relative simplicity as to save computer time. It seems that the theory yields reasonably good estimates for aircraft noise.