The primary effects of aviation on society are cited fairly regularly by both the aviation community and its critics. Papers already presented at this conference and others have reviewed the direct benefits to commerce, economic development, and world trade, and the unfavourable aspects of energy usage and environmental disruption.

There are also some secondary effects which in the long term may prove even more significant. The characteristic influences of improved transportation systems in general are magnified in the case of air transportation because of its greater scope and pace. The growth of a major transportation system eventually transforms almost every facet of society—the distribution of population within and among countries, the evolution of cities, the development of remote areas, the birth of new industries, the advent of multi-national corporations, the location and structure of governments, the interchange of social philosophies, and even the spread of disease. Increased mobility has accelerated the civil rights movements and the pressures for independence throughout the world. The full schedules of sporting events made possible by air transportation create an outlet for national rivalries on a relatively peaceful basis.

It is understandable for fundamental cycle efficiency reasons that the technology level claimed by manufacturers in the development of gas turbines has tended to be judged by the declared maximum TET, but this is not any longer an adequate criterion. A better criterion would be the maximum TET at which it is possible to operate a turbine for a given value of the net turbine shaft efficiency after allowing for all the cooling losses without a penalty in the operating life of the turbine in service.

Figure 1 shows how the specific fuel consumption of turbofan engines varies with turbine entry temperature and overall pressure ratio for different levels of polytropic efficiency of all the components of −2%, +2%, +4% relative to datum. The importance of obtaining the highest possible component efficiencies rather than by further increasing TET and overall pressure ratio (which increase engine complexity and cost), is clearly brought out.

During the incredibly brief period of the last 20 years, a revolution has taken place in air transportation. The magnitude and rapidity of change, and its worldwide impact, are probably unprecedented in history. The earth has shrunk so that no two points are much more than a day apart. World travel has become commonplace, bringing with it sociological changes of immense potential magnitude.

Today we are standing on the threshold of an era of even greater growth in our industry and its contribution to the world.

It is the purpose of this discussion to review progress and promise in the total air transportation system from the standpoint of passengers and freight, geography, technology, economics, regulation, airlines, and manufacturers. I would like to do this in three parts: (i) progress, (ii) uncertainties, and (iii) promise.

One of my US friends in the forecasting fraternity wrote a paper some years ago which he called ‘The Perils of Prediction'. He concluded, on the evidence of successes and failures, that all air traffic forecasters needed to have their heads examined for staying in the business. So why am I here today to talk about air transport demand in the next quarter of a century? Only because I am totally persuaded that the industry cannot do without forecasts —and, moreover, very long term forecasts—of the future volume and nature of demand. I shall examine this proposition in detail shortly. But, in spite of this conviction, you will note that I have added the words ‘through a glass darkly’ to my title. Those of you familiar with St. Paul's Epistle to the Corinthians will remember the words:

'When I was a child, I spoke as a child, I understood as a child, I thought as a child, but when I became a man I put away childish things for now we see through a glass darkly, but then face to face'.

Considerable public debate has arisen recently over the Warsaw Pact's increasing military capability both in quantity and quality of land, sea and air weapons systems. The Soviet military potential has moved from mainly defensive to increased offensive power and a considerable proportion of Soviet resources is going into military research and development. These developments and trends are of increasing concern to the Western democracies particularly in the light of Soviet communism's constant aims and ambitions.

Professional military correspondents and commentators have been warning us on these trends in Soviet military power for a decade or more but a more public and general concern has arisen only in the last year or two, inspired in part perhaps by the lack of progress in SALT and MBFR negotiations as well as the disappointments arising out of the Helsinki agreements.