In aviation we are concerned with vehicles which, for the majority of their journey time, are well separated from the community by a vertical distance of some 5-8 miles. Over most of their flight they are the cleanest and quietest form of transport. The aircraft noise problem therefore is confined to the regions around the terminal area. The object of this paper is to define aircraft noise sources and to discuss means by which the terminal noise of advanced air-transport systems can be limited, in order to minimize the noise nuisance. From the mid-1950’s to the mid-19603 there had been a steady build-up in the noise of commercial aircraft operations due to the introduction of jet transports and the steady increase in both aircraft size and number of movements. In the early part of the last decade public reaction to the noise situation was slow. Jet transports were seen as an advance in technology and many were proud to be associated with their introduction. Although manufacturers were aware of the undesirable noise characteristics of the jet engine, technological advances were aimed more at improving thrust performance and cruise efficiency in order to achieve significant increases in range. The first step towards noise improvement was the introduction of the low by-pass/turbofan engines in the early 1960’s, which although quieter, did not make a significant impact on the noise scene. However, the introduction of the advanced high by-pass ratio engines which power today’s wide-bodied airliners has improved the noise situation dramatically (see Figure 1). Initially the use of high by-pass ratios was probably aimed more at the improvement of performance and economics than at noise reduction. However, as time went by and the environmental lobby became stronger, the emphasis on design for low noise increased. Regulatory bodies like the FAA and ICAO formulated noise requirements and certification rules which reflected public pressures to curtail the aircraft noise.