The perceived unpleasantness due to aircraft flyover noise is mostly explained by a) non-acoustical factors, and b) the noise level, on which future progress will be prospectively hard and expensive to obtain. However, the literature suggests that sound-quality approaches may provide new solutions for reducing the perceived unpleasantness. The study reported here investigates the effects of the temporal parameters of single aircraft flyover sound signatures on the unpleasantness experienced by people outside the aircraft. Two listening tests (semantic differential, synthesised stimuli) were conducted. In the first test the stimuli were equalised according to the EPNL in order to concentrate on the slope, duration and amount of fluctuation of the sound signatures. In the second test the influences of the temporal aspects and of the noise level were compared. Statistical analyses were performed. Although slope and duration were made independent, their perceptions remain correlated. Descriptors are proposed for assessing the duration and the amount of fluctuation. For both configurations (stimuli equalised or not), a model is proposed, in which the unpleasantness is explained by the duration, the amount of fluctuation and the noise level. Unsurprisingly the noise level is the most influential factor for the unpleasantness, but the temporal factors are also important. The amount of fluctuation strongly correlates with the unpleasantness. The duration has a two-sided effect: short flyover noises exhibit higher peak levels and so increase the unpleasantness; long flyover noises maximise the length of sound exposure and also increase the unpleasantness.