The June 1963 Report of the Inter-Departmental Committee on the Third London Airport concluded that a third London Airport would be required in the early 1970's, and possibly a fourth soon after 1980. It also brought out that because of the large amounts of air space required for the sequencing areas and approach paths of each airport, and because of limitations imposed by the positioning of the main air traffic routeings, the choice of possible sites within reasonable distance of Central London for the third airport was severely restricted. In a postscript to the Report, it was recognised that after the third airport has taken over a further block of air space, the difficulty of siting a fourth airport would be even more severe.