This paper discusses the technical problems of traffic flow encountered in the overall design of a communication system for a specific purpose, namely the provision of air-traffic services to civil aircraft. The major part of the paper deals with(a) the evaluation of queueing delays on aeronautical mobile (aeromobile) speech channels, from which the number of channels required to meet a chosen delay criterion is estimated(b) the minimum signal/noise ratio required for satisfactory communication on aeronautical radio channels, and the transmitter power required to produce it.Statistics of operator loading, channel holding times and message-arrival rates are given, and the role of the human operator as a component of the system is evaluated.