Before considering the special case of the North Atlantic, I should like to attempt some clarification of the term “Air Traffic Control” (A.T.C.). It is in fact a service for which I.C.A.O. member states have accepted responsibility dedicated primarily to avoidance of air-to-air collision hazards and secondly, to providing an expeditious traffic flow. When traffic is dense these requirements are somewhat incompatible and, of course, safety considerations are paramount; therefore the traffic flow suffers impediment in some form or other. Traffic Controllers provide service by issuing clearances which are subject to pilot acceptance. Pilots can ask for alternative clearances if they deem those offered unacceptable. Although the A.T.C. service clearly shoulders a large measure of responsibility for avoidance of air-to-air collisions, the ultimate responsibility is vested in the pilot-in-command who is authorised to take any action he considers necessary to maintain safe flight.