It is almost two years since Wing Commander Dickie's survey (11, 259) emphasized the importance of improving methods of control so as to allow more movements in a given volume of airspace. Since then, much effort in many countries has been devoted to the problem. The magnitude of these difficulties is not surprising when it is recalled that, in addition to the professional difficulties of flying, navigation and control, various sections of industry are involved, and international agreement must be obtained. At every turn there are political and commercial problems which cannot be ignored by those responsible for initiating action to solve a very difficult practical problem. This note is written in an attempt to examine once again the various possibilities for improving airspace utilization, with the object of discovering some pattern which will lead to progress.

It has been stated that at all times both the controller and the pilot must know the absolute ground position of the aircraft, but it is by no means clear that this really is a requirement. It could well be sufficient to maintain the position of the aircraft relative to the traffic pattern, for this would satisfy the pilot's aim which is to travel in accordance with his flight plan, and also the controller's aim which is to ensure safety while making best use of the available airspace.