In his Presidential Address at the Annual General Meeting of the Institute, Captain Majendie spent some time on demonstrating the restrictions imposed on free navigation by air traffic control. Whilst there is much truth in his statement the matter does not end there and I believe that those who study his address in retrospect should remember that the marked inflexibility of economic operation in the vertical plane of the modern jet aircraft and, to a lesser extent, the turbo-propeller driven aircraft, imposes considerable restrictions on air traffic control! In fact, the designers of modern aircraft and engines seem to be doing their best to deprive air traffic of its unique asset—the third dimension.