Long-range transport aircraft of the next decade will almost certainly contain a navigation system capable of providing accurate and reliable fixing and flight director information over any part of the world. Over the North Atlantic Ocean die navigation system must be reliable enough to ensure safety at an agreed separation between aircraft flying in a controlled environment. At the conclusion of the en-route part of a flight these long-range aircraft pass through an interface of some 200 or 300 n.m. radius around the terminal airfield before they come within the close terminal control, with its specialized aids to approach, landing, take-off guidance and holding. The interface is currently served by a variety of radio and radar aids, all ground based at the present time. Aircraft are monitored by primary radar on the ground while they fly along airways some 10 n.m. wide with the aid of VOR/DME, Decca/Harco or A.D.F. The aids used depend upon the traffic density experienced in the area, the geographical environment and many other factors. At this time when consideration must be given to the development of an accepted navigation system for the interface, it is important that close attention should be given to the employment wherever possible of a rational navigation system compatible with all en-route systems and terminal area aids. The system used in the interface should use as much of die en-route and terminal equipment as possible, perhaps eventually removing the airways interface, as we know it, altogedier. Several techniques should be considered, diey include die use of ground radar for die precise up-dating of doppler and inertia navigation aids, die use of differential Omega for up-dating widi conventional Omega and ground radar for gross-error monitoring, and die use of ILS localizer beams used in conjunction with a downwind localizer aerial for the provision of a service presendy supplied by VOR and ADF.