Traffic growth and the replacement of the older, less efficient and noisier aircraft—60% of Western World capacity may be regarded as in this category—provide the opportunity for applying new technologies to subsonic commercial transports. Reduction of operating cost continues to provide the major incentive, though increasing emphasis is being placed on low fuel consumption and low noise.

In this paper, the term ‘advanced technology’ is taken to embrace significant engineering advances which are not commonplace on aircraft flying today. In general, it is wrong to think of such advances as new inventions. Almost without exception they have evolved over the years, with few quantum jumps. There are, of course, exceptions to this and a recent example as regards engine development might be the introduction of high bypass ratio engines in the late 1960s, which brought about a 25% improvement in specific fuel consumption. However, even this major step could be regarded as an evolutionary development from engines of bypass ratio about 1·0, which themselves had conferred significant gains relative to the straight turbo-jet engines of the late 1950s.