The objective of this study was to obtain factual data on existing background noise levels and on actual noise levels of 'classical' aircraft en-route in Europe and elsewhere. Such data is needed as studies are done on supersonic business jets and the so called 'open rotor' engines. They have a common factor in that they will potentially create non negligible noise levels on the ground, not only when flying in the terminal area around airports but also while the aircraft are climbing, cruising and descending at distance from airports (referred to as "en-route noise"). If aircraft with such technology would be numerous, this could mean that aircraft noise might be audible almost everywhere. In order to inform the political discussion and the regulatory impact assessment, it is necessary to put the noise levels of the new technologies in perspective with the current situation.