In the Introduction to the second paper in this series (September 1965 IOURNAL), a simple flow diagram illustrates the relationship between demand and supply for aircraft and air transport which is shown in Fig. 1.
Manufacturers supply airlines with aircraft from which a fleet is built. The airlines are thus faced with problems of capital investment and procurement programmes, which were discussed under the heading of fixed costs in the second paper.
The discussion of problems of fleet effectiveness and optimal utilisation begun in the second paper, and elaborated in the third (October 1965 JOURNAL), is continued in Section A of the present one.
Attention is then switched in Section B to the demand for air transport. On the basis of demand for transport of passengers and freight, airlines must determine routes, allocate frequencies to these routes, and prepare time-tables.
The paper concludes the discussion of Operational Research applied to airlines by summarising the models used in the series in the light of the aims specified in the first paper (August .1965 JOURNAL).