This paper, which was presented at a meeting of the Institute in London on 2o May 1981, with Captain R. Maybourn in the Chair, describes some studies of the conflicts arising between a multiplicity of aircraft in straight-line flight through a volume of airspace. Topics include the effect of coercing traffic to fly fixed routes, the direction from which a threat can be expected and the choice of alerting criterion for a groundbased advisory service or an airborne collision-warning system. There are some analogies, perhaps, with marine traffic problems.There exists, worldwide, a complex scheme for the segregation and control of various classes of air traffic. To fit into this scheme aircraft must make detours, horizontally and/or vertically, the cost of which in Europe alone must be at least £50M per annum. The cost of the rare failures in traffic management is higher still. To authors trained in electronic engineering it is therefore rather surprising that the published theory of air traffic management and control is still in a rather rudimentary form.
A recent paper by Cox, ten Have and Forrester is planned to be the first of a series describing the work of the European Vertical Studies Sub Group (VSSG) set up under the ICAO panel for review of the general concept of separation. The present paper has no connection with the VSSG work.
For many years there has been keen interest, especially in the avionics industry, in the possibility of devising some airborne device which would warn aircrew of an impending mid-air collision. At sea, the use of radar as a collision-warning device is now common, and the carriage of a computer-based collision warning device on tankers in US waters is expected to become mandatory in the near future.
In an earlier study, the author attempted to give some quantitative estimates of the problems
that free flow might face in Europe. The study was based on a traffic sample from the
Eurocontrol Route Charges Office for a busy day in 1991. More recently, they generously
made available a similar sample for a day in 1997. Using this new data, the study has been
extended to cover wider aspects of the free flow problem. The central problem is that of
ensuring safety. This will require a mechanism to detect collision threats and safely to resolve
the problems. Possible tools are ground-based surveillance and/or airborne systems. This
paper will use computer modelling to predict the loads that these detection and resolution
systems must face.
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